2 * Budget Fair Queueing (BFQ) I/O scheduler.
4 * Based on ideas and code from CFQ:
5 * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
7 * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
8 * Paolo Valente <paolo.valente@unimore.it>
10 * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
11 * Arianna Avanzini <avanzini@google.com>
13 * Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org>
15 * This program is free software; you can redistribute it and/or
16 * modify it under the terms of the GNU General Public License as
17 * published by the Free Software Foundation; either version 2 of the
18 * License, or (at your option) any later version.
20 * This program is distributed in the hope that it will be useful,
21 * but WITHOUT ANY WARRANTY; without even the implied warranty of
22 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 * General Public License for more details.
25 * BFQ is a proportional-share I/O scheduler, with some extra
26 * low-latency capabilities. BFQ also supports full hierarchical
27 * scheduling through cgroups. Next paragraphs provide an introduction
28 * on BFQ inner workings. Details on BFQ benefits, usage and
29 * limitations can be found in Documentation/block/bfq-iosched.txt.
31 * BFQ is a proportional-share storage-I/O scheduling algorithm based
32 * on the slice-by-slice service scheme of CFQ. But BFQ assigns
33 * budgets, measured in number of sectors, to processes instead of
34 * time slices. The device is not granted to the in-service process
35 * for a given time slice, but until it has exhausted its assigned
36 * budget. This change from the time to the service domain enables BFQ
37 * to distribute the device throughput among processes as desired,
38 * without any distortion due to throughput fluctuations, or to device
39 * internal queueing. BFQ uses an ad hoc internal scheduler, called
40 * B-WF2Q+, to schedule processes according to their budgets. More
41 * precisely, BFQ schedules queues associated with processes. Each
42 * process/queue is assigned a user-configurable weight, and B-WF2Q+
43 * guarantees that each queue receives a fraction of the throughput
44 * proportional to its weight. Thanks to the accurate policy of
45 * B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound
46 * processes issuing sequential requests (to boost the throughput),
47 * and yet guarantee a low latency to interactive and soft real-time
50 * In particular, to provide these low-latency guarantees, BFQ
51 * explicitly privileges the I/O of two classes of time-sensitive
52 * applications: interactive and soft real-time. This feature enables
53 * BFQ to provide applications in these classes with a very low
54 * latency. Finally, BFQ also features additional heuristics for
55 * preserving both a low latency and a high throughput on NCQ-capable,
56 * rotational or flash-based devices, and to get the job done quickly
57 * for applications consisting in many I/O-bound processes.
59 * NOTE: if the main or only goal, with a given device, is to achieve
60 * the maximum-possible throughput at all times, then do switch off
61 * all low-latency heuristics for that device, by setting low_latency
64 * BFQ is described in [1], where also a reference to the initial, more
65 * theoretical paper on BFQ can be found. The interested reader can find
66 * in the latter paper full details on the main algorithm, as well as
67 * formulas of the guarantees and formal proofs of all the properties.
68 * With respect to the version of BFQ presented in these papers, this
69 * implementation adds a few more heuristics, such as the one that
70 * guarantees a low latency to soft real-time applications, and a
71 * hierarchical extension based on H-WF2Q+.
73 * B-WF2Q+ is based on WF2Q+, which is described in [2], together with
74 * H-WF2Q+, while the augmented tree used here to implement B-WF2Q+
75 * with O(log N) complexity derives from the one introduced with EEVDF
78 * [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
79 * Scheduler", Proceedings of the First Workshop on Mobile System
80 * Technologies (MST-2015), May 2015.
81 * http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf
83 * [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing
84 * Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689,
87 * http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz
89 * [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline
90 * First: A Flexible and Accurate Mechanism for Proportional Share
91 * Resource Allocation", technical report.
93 * http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf
95 #include <linux/module.h>
96 #include <linux/slab.h>
97 #include <linux/blkdev.h>
98 #include <linux/cgroup.h>
99 #include <linux/elevator.h>
100 #include <linux/ktime.h>
101 #include <linux/rbtree.h>
102 #include <linux/ioprio.h>
103 #include <linux/sbitmap.h>
104 #include <linux/delay.h>
108 #include "blk-mq-tag.h"
109 #include "blk-mq-sched.h"
110 #include "bfq-iosched.h"
113 #define BFQ_BFQQ_FNS(name) \
114 void bfq_mark_bfqq_##name(struct bfq_queue *bfqq) \
116 __set_bit(BFQQF_##name, &(bfqq)->flags); \
118 void bfq_clear_bfqq_##name(struct bfq_queue *bfqq) \
120 __clear_bit(BFQQF_##name, &(bfqq)->flags); \
122 int bfq_bfqq_##name(const struct bfq_queue *bfqq) \
124 return test_bit(BFQQF_##name, &(bfqq)->flags); \
127 BFQ_BFQQ_FNS(just_created
);
129 BFQ_BFQQ_FNS(wait_request
);
130 BFQ_BFQQ_FNS(non_blocking_wait_rq
);
131 BFQ_BFQQ_FNS(fifo_expire
);
132 BFQ_BFQQ_FNS(has_short_ttime
);
134 BFQ_BFQQ_FNS(IO_bound
);
135 BFQ_BFQQ_FNS(in_large_burst
);
137 BFQ_BFQQ_FNS(split_coop
);
138 BFQ_BFQQ_FNS(softrt_update
);
139 #undef BFQ_BFQQ_FNS \
141 /* Expiration time of sync (0) and async (1) requests, in ns. */
142 static const u64 bfq_fifo_expire
[2] = { NSEC_PER_SEC
/ 4, NSEC_PER_SEC
/ 8 };
144 /* Maximum backwards seek (magic number lifted from CFQ), in KiB. */
145 static const int bfq_back_max
= 16 * 1024;
147 /* Penalty of a backwards seek, in number of sectors. */
148 static const int bfq_back_penalty
= 2;
150 /* Idling period duration, in ns. */
151 static u64 bfq_slice_idle
= NSEC_PER_SEC
/ 125;
153 /* Minimum number of assigned budgets for which stats are safe to compute. */
154 static const int bfq_stats_min_budgets
= 194;
156 /* Default maximum budget values, in sectors and number of requests. */
157 static const int bfq_default_max_budget
= 16 * 1024;
160 * Async to sync throughput distribution is controlled as follows:
161 * when an async request is served, the entity is charged the number
162 * of sectors of the request, multiplied by the factor below
164 static const int bfq_async_charge_factor
= 10;
166 /* Default timeout values, in jiffies, approximating CFQ defaults. */
167 const int bfq_timeout
= HZ
/ 8;
169 static struct kmem_cache
*bfq_pool
;
171 /* Below this threshold (in ns), we consider thinktime immediate. */
172 #define BFQ_MIN_TT (2 * NSEC_PER_MSEC)
174 /* hw_tag detection: parallel requests threshold and min samples needed. */
175 #define BFQ_HW_QUEUE_THRESHOLD 4
176 #define BFQ_HW_QUEUE_SAMPLES 32
178 #define BFQQ_SEEK_THR (sector_t)(8 * 100)
179 #define BFQQ_SECT_THR_NONROT (sector_t)(2 * 32)
180 #define BFQQ_CLOSE_THR (sector_t)(8 * 1024)
181 #define BFQQ_SEEKY(bfqq) (hweight32(bfqq->seek_history) > 32/8)
183 /* Min number of samples required to perform peak-rate update */
184 #define BFQ_RATE_MIN_SAMPLES 32
185 /* Min observation time interval required to perform a peak-rate update (ns) */
186 #define BFQ_RATE_MIN_INTERVAL (300*NSEC_PER_MSEC)
187 /* Target observation time interval for a peak-rate update (ns) */
188 #define BFQ_RATE_REF_INTERVAL NSEC_PER_SEC
190 /* Shift used for peak rate fixed precision calculations. */
191 #define BFQ_RATE_SHIFT 16
194 * By default, BFQ computes the duration of the weight raising for
195 * interactive applications automatically, using the following formula:
196 * duration = (R / r) * T, where r is the peak rate of the device, and
197 * R and T are two reference parameters.
198 * In particular, R is the peak rate of the reference device (see below),
199 * and T is a reference time: given the systems that are likely to be
200 * installed on the reference device according to its speed class, T is
201 * about the maximum time needed, under BFQ and while reading two files in
202 * parallel, to load typical large applications on these systems.
203 * In practice, the slower/faster the device at hand is, the more/less it
204 * takes to load applications with respect to the reference device.
205 * Accordingly, the longer/shorter BFQ grants weight raising to interactive
208 * BFQ uses four different reference pairs (R, T), depending on:
209 * . whether the device is rotational or non-rotational;
210 * . whether the device is slow, such as old or portable HDDs, as well as
211 * SD cards, or fast, such as newer HDDs and SSDs.
213 * The device's speed class is dynamically (re)detected in
214 * bfq_update_peak_rate() every time the estimated peak rate is updated.
216 * In the following definitions, R_slow[0]/R_fast[0] and
217 * T_slow[0]/T_fast[0] are the reference values for a slow/fast
218 * rotational device, whereas R_slow[1]/R_fast[1] and
219 * T_slow[1]/T_fast[1] are the reference values for a slow/fast
220 * non-rotational device. Finally, device_speed_thresh are the
221 * thresholds used to switch between speed classes. The reference
222 * rates are not the actual peak rates of the devices used as a
223 * reference, but slightly lower values. The reason for using these
224 * slightly lower values is that the peak-rate estimator tends to
225 * yield slightly lower values than the actual peak rate (it can yield
226 * the actual peak rate only if there is only one process doing I/O,
227 * and the process does sequential I/O).
229 * Both the reference peak rates and the thresholds are measured in
230 * sectors/usec, left-shifted by BFQ_RATE_SHIFT.
232 static int R_slow
[2] = {1000, 10700};
233 static int R_fast
[2] = {14000, 33000};
235 * To improve readability, a conversion function is used to initialize the
236 * following arrays, which entails that they can be initialized only in a
239 static int T_slow
[2];
240 static int T_fast
[2];
241 static int device_speed_thresh
[2];
243 #define RQ_BIC(rq) icq_to_bic((rq)->elv.priv[0])
244 #define RQ_BFQQ(rq) ((rq)->elv.priv[1])
246 struct bfq_queue
*bic_to_bfqq(struct bfq_io_cq
*bic
, bool is_sync
)
248 return bic
->bfqq
[is_sync
];
251 void bic_set_bfqq(struct bfq_io_cq
*bic
, struct bfq_queue
*bfqq
, bool is_sync
)
253 bic
->bfqq
[is_sync
] = bfqq
;
256 struct bfq_data
*bic_to_bfqd(struct bfq_io_cq
*bic
)
258 return bic
->icq
.q
->elevator
->elevator_data
;
262 * icq_to_bic - convert iocontext queue structure to bfq_io_cq.
263 * @icq: the iocontext queue.
265 static struct bfq_io_cq
*icq_to_bic(struct io_cq
*icq
)
267 /* bic->icq is the first member, %NULL will convert to %NULL */
268 return container_of(icq
, struct bfq_io_cq
, icq
);
272 * bfq_bic_lookup - search into @ioc a bic associated to @bfqd.
273 * @bfqd: the lookup key.
274 * @ioc: the io_context of the process doing I/O.
275 * @q: the request queue.
277 static struct bfq_io_cq
*bfq_bic_lookup(struct bfq_data
*bfqd
,
278 struct io_context
*ioc
,
279 struct request_queue
*q
)
283 struct bfq_io_cq
*icq
;
285 spin_lock_irqsave(q
->queue_lock
, flags
);
286 icq
= icq_to_bic(ioc_lookup_icq(ioc
, q
));
287 spin_unlock_irqrestore(q
->queue_lock
, flags
);
296 * Scheduler run of queue, if there are requests pending and no one in the
297 * driver that will restart queueing.
299 void bfq_schedule_dispatch(struct bfq_data
*bfqd
)
301 if (bfqd
->queued
!= 0) {
302 bfq_log(bfqd
, "schedule dispatch");
303 blk_mq_run_hw_queues(bfqd
->queue
, true);
307 #define bfq_class_idle(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
308 #define bfq_class_rt(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_RT)
310 #define bfq_sample_valid(samples) ((samples) > 80)
313 * Lifted from AS - choose which of rq1 and rq2 that is best served now.
314 * We choose the request that is closesr to the head right now. Distance
315 * behind the head is penalized and only allowed to a certain extent.
317 static struct request
*bfq_choose_req(struct bfq_data
*bfqd
,
322 sector_t s1
, s2
, d1
= 0, d2
= 0;
323 unsigned long back_max
;
324 #define BFQ_RQ1_WRAP 0x01 /* request 1 wraps */
325 #define BFQ_RQ2_WRAP 0x02 /* request 2 wraps */
326 unsigned int wrap
= 0; /* bit mask: requests behind the disk head? */
328 if (!rq1
|| rq1
== rq2
)
333 if (rq_is_sync(rq1
) && !rq_is_sync(rq2
))
335 else if (rq_is_sync(rq2
) && !rq_is_sync(rq1
))
337 if ((rq1
->cmd_flags
& REQ_META
) && !(rq2
->cmd_flags
& REQ_META
))
339 else if ((rq2
->cmd_flags
& REQ_META
) && !(rq1
->cmd_flags
& REQ_META
))
342 s1
= blk_rq_pos(rq1
);
343 s2
= blk_rq_pos(rq2
);
346 * By definition, 1KiB is 2 sectors.
348 back_max
= bfqd
->bfq_back_max
* 2;
351 * Strict one way elevator _except_ in the case where we allow
352 * short backward seeks which are biased as twice the cost of a
353 * similar forward seek.
357 else if (s1
+ back_max
>= last
)
358 d1
= (last
- s1
) * bfqd
->bfq_back_penalty
;
360 wrap
|= BFQ_RQ1_WRAP
;
364 else if (s2
+ back_max
>= last
)
365 d2
= (last
- s2
) * bfqd
->bfq_back_penalty
;
367 wrap
|= BFQ_RQ2_WRAP
;
369 /* Found required data */
372 * By doing switch() on the bit mask "wrap" we avoid having to
373 * check two variables for all permutations: --> faster!
376 case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
391 case BFQ_RQ1_WRAP
|BFQ_RQ2_WRAP
: /* both rqs wrapped */
394 * Since both rqs are wrapped,
395 * start with the one that's further behind head
396 * (--> only *one* back seek required),
397 * since back seek takes more time than forward.
406 static struct bfq_queue
*
407 bfq_rq_pos_tree_lookup(struct bfq_data
*bfqd
, struct rb_root
*root
,
408 sector_t sector
, struct rb_node
**ret_parent
,
409 struct rb_node
***rb_link
)
411 struct rb_node
**p
, *parent
;
412 struct bfq_queue
*bfqq
= NULL
;
420 bfqq
= rb_entry(parent
, struct bfq_queue
, pos_node
);
423 * Sort strictly based on sector. Smallest to the left,
424 * largest to the right.
426 if (sector
> blk_rq_pos(bfqq
->next_rq
))
428 else if (sector
< blk_rq_pos(bfqq
->next_rq
))
436 *ret_parent
= parent
;
440 bfq_log(bfqd
, "rq_pos_tree_lookup %llu: returning %d",
441 (unsigned long long)sector
,
442 bfqq
? bfqq
->pid
: 0);
447 void bfq_pos_tree_add_move(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
449 struct rb_node
**p
, *parent
;
450 struct bfq_queue
*__bfqq
;
452 if (bfqq
->pos_root
) {
453 rb_erase(&bfqq
->pos_node
, bfqq
->pos_root
);
454 bfqq
->pos_root
= NULL
;
457 if (bfq_class_idle(bfqq
))
462 bfqq
->pos_root
= &bfq_bfqq_to_bfqg(bfqq
)->rq_pos_tree
;
463 __bfqq
= bfq_rq_pos_tree_lookup(bfqd
, bfqq
->pos_root
,
464 blk_rq_pos(bfqq
->next_rq
), &parent
, &p
);
466 rb_link_node(&bfqq
->pos_node
, parent
, p
);
467 rb_insert_color(&bfqq
->pos_node
, bfqq
->pos_root
);
469 bfqq
->pos_root
= NULL
;
473 * Tell whether there are active queues or groups with differentiated weights.
475 static bool bfq_differentiated_weights(struct bfq_data
*bfqd
)
478 * For weights to differ, at least one of the trees must contain
479 * at least two nodes.
481 return (!RB_EMPTY_ROOT(&bfqd
->queue_weights_tree
) &&
482 (bfqd
->queue_weights_tree
.rb_node
->rb_left
||
483 bfqd
->queue_weights_tree
.rb_node
->rb_right
)
484 #ifdef CONFIG_BFQ_GROUP_IOSCHED
486 (!RB_EMPTY_ROOT(&bfqd
->group_weights_tree
) &&
487 (bfqd
->group_weights_tree
.rb_node
->rb_left
||
488 bfqd
->group_weights_tree
.rb_node
->rb_right
)
494 * The following function returns true if every queue must receive the
495 * same share of the throughput (this condition is used when deciding
496 * whether idling may be disabled, see the comments in the function
497 * bfq_bfqq_may_idle()).
499 * Such a scenario occurs when:
500 * 1) all active queues have the same weight,
501 * 2) all active groups at the same level in the groups tree have the same
503 * 3) all active groups at the same level in the groups tree have the same
504 * number of children.
506 * Unfortunately, keeping the necessary state for evaluating exactly the
507 * above symmetry conditions would be quite complex and time-consuming.
508 * Therefore this function evaluates, instead, the following stronger
509 * sub-conditions, for which it is much easier to maintain the needed
511 * 1) all active queues have the same weight,
512 * 2) all active groups have the same weight,
513 * 3) all active groups have at most one active child each.
514 * In particular, the last two conditions are always true if hierarchical
515 * support and the cgroups interface are not enabled, thus no state needs
516 * to be maintained in this case.
518 static bool bfq_symmetric_scenario(struct bfq_data
*bfqd
)
520 return !bfq_differentiated_weights(bfqd
);
524 * If the weight-counter tree passed as input contains no counter for
525 * the weight of the input entity, then add that counter; otherwise just
526 * increment the existing counter.
528 * Note that weight-counter trees contain few nodes in mostly symmetric
529 * scenarios. For example, if all queues have the same weight, then the
530 * weight-counter tree for the queues may contain at most one node.
531 * This holds even if low_latency is on, because weight-raised queues
532 * are not inserted in the tree.
533 * In most scenarios, the rate at which nodes are created/destroyed
536 void bfq_weights_tree_add(struct bfq_data
*bfqd
, struct bfq_entity
*entity
,
537 struct rb_root
*root
)
539 struct rb_node
**new = &(root
->rb_node
), *parent
= NULL
;
542 * Do not insert if the entity is already associated with a
543 * counter, which happens if:
544 * 1) the entity is associated with a queue,
545 * 2) a request arrival has caused the queue to become both
546 * non-weight-raised, and hence change its weight, and
547 * backlogged; in this respect, each of the two events
548 * causes an invocation of this function,
549 * 3) this is the invocation of this function caused by the
550 * second event. This second invocation is actually useless,
551 * and we handle this fact by exiting immediately. More
552 * efficient or clearer solutions might possibly be adopted.
554 if (entity
->weight_counter
)
558 struct bfq_weight_counter
*__counter
= container_of(*new,
559 struct bfq_weight_counter
,
563 if (entity
->weight
== __counter
->weight
) {
564 entity
->weight_counter
= __counter
;
567 if (entity
->weight
< __counter
->weight
)
568 new = &((*new)->rb_left
);
570 new = &((*new)->rb_right
);
573 entity
->weight_counter
= kzalloc(sizeof(struct bfq_weight_counter
),
577 * In the unlucky event of an allocation failure, we just
578 * exit. This will cause the weight of entity to not be
579 * considered in bfq_differentiated_weights, which, in its
580 * turn, causes the scenario to be deemed wrongly symmetric in
581 * case entity's weight would have been the only weight making
582 * the scenario asymmetric. On the bright side, no unbalance
583 * will however occur when entity becomes inactive again (the
584 * invocation of this function is triggered by an activation
585 * of entity). In fact, bfq_weights_tree_remove does nothing
586 * if !entity->weight_counter.
588 if (unlikely(!entity
->weight_counter
))
591 entity
->weight_counter
->weight
= entity
->weight
;
592 rb_link_node(&entity
->weight_counter
->weights_node
, parent
, new);
593 rb_insert_color(&entity
->weight_counter
->weights_node
, root
);
596 entity
->weight_counter
->num_active
++;
600 * Decrement the weight counter associated with the entity, and, if the
601 * counter reaches 0, remove the counter from the tree.
602 * See the comments to the function bfq_weights_tree_add() for considerations
605 void bfq_weights_tree_remove(struct bfq_data
*bfqd
, struct bfq_entity
*entity
,
606 struct rb_root
*root
)
608 if (!entity
->weight_counter
)
611 entity
->weight_counter
->num_active
--;
612 if (entity
->weight_counter
->num_active
> 0)
613 goto reset_entity_pointer
;
615 rb_erase(&entity
->weight_counter
->weights_node
, root
);
616 kfree(entity
->weight_counter
);
618 reset_entity_pointer
:
619 entity
->weight_counter
= NULL
;
623 * Return expired entry, or NULL to just start from scratch in rbtree.
625 static struct request
*bfq_check_fifo(struct bfq_queue
*bfqq
,
626 struct request
*last
)
630 if (bfq_bfqq_fifo_expire(bfqq
))
633 bfq_mark_bfqq_fifo_expire(bfqq
);
635 rq
= rq_entry_fifo(bfqq
->fifo
.next
);
637 if (rq
== last
|| ktime_get_ns() < rq
->fifo_time
)
640 bfq_log_bfqq(bfqq
->bfqd
, bfqq
, "check_fifo: returned %p", rq
);
644 static struct request
*bfq_find_next_rq(struct bfq_data
*bfqd
,
645 struct bfq_queue
*bfqq
,
646 struct request
*last
)
648 struct rb_node
*rbnext
= rb_next(&last
->rb_node
);
649 struct rb_node
*rbprev
= rb_prev(&last
->rb_node
);
650 struct request
*next
, *prev
= NULL
;
652 /* Follow expired path, else get first next available. */
653 next
= bfq_check_fifo(bfqq
, last
);
658 prev
= rb_entry_rq(rbprev
);
661 next
= rb_entry_rq(rbnext
);
663 rbnext
= rb_first(&bfqq
->sort_list
);
664 if (rbnext
&& rbnext
!= &last
->rb_node
)
665 next
= rb_entry_rq(rbnext
);
668 return bfq_choose_req(bfqd
, next
, prev
, blk_rq_pos(last
));
671 /* see the definition of bfq_async_charge_factor for details */
672 static unsigned long bfq_serv_to_charge(struct request
*rq
,
673 struct bfq_queue
*bfqq
)
675 if (bfq_bfqq_sync(bfqq
) || bfqq
->wr_coeff
> 1)
676 return blk_rq_sectors(rq
);
679 * If there are no weight-raised queues, then amplify service
680 * by just the async charge factor; otherwise amplify service
681 * by twice the async charge factor, to further reduce latency
682 * for weight-raised queues.
684 if (bfqq
->bfqd
->wr_busy_queues
== 0)
685 return blk_rq_sectors(rq
) * bfq_async_charge_factor
;
687 return blk_rq_sectors(rq
) * 2 * bfq_async_charge_factor
;
691 * bfq_updated_next_req - update the queue after a new next_rq selection.
692 * @bfqd: the device data the queue belongs to.
693 * @bfqq: the queue to update.
695 * If the first request of a queue changes we make sure that the queue
696 * has enough budget to serve at least its first request (if the
697 * request has grown). We do this because if the queue has not enough
698 * budget for its first request, it has to go through two dispatch
699 * rounds to actually get it dispatched.
701 static void bfq_updated_next_req(struct bfq_data
*bfqd
,
702 struct bfq_queue
*bfqq
)
704 struct bfq_entity
*entity
= &bfqq
->entity
;
705 struct request
*next_rq
= bfqq
->next_rq
;
706 unsigned long new_budget
;
711 if (bfqq
== bfqd
->in_service_queue
)
713 * In order not to break guarantees, budgets cannot be
714 * changed after an entity has been selected.
718 new_budget
= max_t(unsigned long, bfqq
->max_budget
,
719 bfq_serv_to_charge(next_rq
, bfqq
));
720 if (entity
->budget
!= new_budget
) {
721 entity
->budget
= new_budget
;
722 bfq_log_bfqq(bfqd
, bfqq
, "updated next rq: new budget %lu",
724 bfq_requeue_bfqq(bfqd
, bfqq
, false);
728 static unsigned int bfq_wr_duration(struct bfq_data
*bfqd
)
732 if (bfqd
->bfq_wr_max_time
> 0)
733 return bfqd
->bfq_wr_max_time
;
736 do_div(dur
, bfqd
->peak_rate
);
739 * Limit duration between 3 and 13 seconds. Tests show that
740 * higher values than 13 seconds often yield the opposite of
741 * the desired result, i.e., worsen responsiveness by letting
742 * non-interactive and non-soft-real-time applications
743 * preserve weight raising for a too long time interval.
745 * On the other end, lower values than 3 seconds make it
746 * difficult for most interactive tasks to complete their jobs
747 * before weight-raising finishes.
749 if (dur
> msecs_to_jiffies(13000))
750 dur
= msecs_to_jiffies(13000);
751 else if (dur
< msecs_to_jiffies(3000))
752 dur
= msecs_to_jiffies(3000);
757 /* switch back from soft real-time to interactive weight raising */
758 static void switch_back_to_interactive_wr(struct bfq_queue
*bfqq
,
759 struct bfq_data
*bfqd
)
761 bfqq
->wr_coeff
= bfqd
->bfq_wr_coeff
;
762 bfqq
->wr_cur_max_time
= bfq_wr_duration(bfqd
);
763 bfqq
->last_wr_start_finish
= bfqq
->wr_start_at_switch_to_srt
;
767 bfq_bfqq_resume_state(struct bfq_queue
*bfqq
, struct bfq_data
*bfqd
,
768 struct bfq_io_cq
*bic
, bool bfq_already_existing
)
770 unsigned int old_wr_coeff
= bfqq
->wr_coeff
;
771 bool busy
= bfq_already_existing
&& bfq_bfqq_busy(bfqq
);
773 if (bic
->saved_has_short_ttime
)
774 bfq_mark_bfqq_has_short_ttime(bfqq
);
776 bfq_clear_bfqq_has_short_ttime(bfqq
);
778 if (bic
->saved_IO_bound
)
779 bfq_mark_bfqq_IO_bound(bfqq
);
781 bfq_clear_bfqq_IO_bound(bfqq
);
783 bfqq
->ttime
= bic
->saved_ttime
;
784 bfqq
->wr_coeff
= bic
->saved_wr_coeff
;
785 bfqq
->wr_start_at_switch_to_srt
= bic
->saved_wr_start_at_switch_to_srt
;
786 bfqq
->last_wr_start_finish
= bic
->saved_last_wr_start_finish
;
787 bfqq
->wr_cur_max_time
= bic
->saved_wr_cur_max_time
;
789 if (bfqq
->wr_coeff
> 1 && (bfq_bfqq_in_large_burst(bfqq
) ||
790 time_is_before_jiffies(bfqq
->last_wr_start_finish
+
791 bfqq
->wr_cur_max_time
))) {
792 if (bfqq
->wr_cur_max_time
== bfqd
->bfq_wr_rt_max_time
&&
793 !bfq_bfqq_in_large_burst(bfqq
) &&
794 time_is_after_eq_jiffies(bfqq
->wr_start_at_switch_to_srt
+
795 bfq_wr_duration(bfqd
))) {
796 switch_back_to_interactive_wr(bfqq
, bfqd
);
799 bfq_log_bfqq(bfqq
->bfqd
, bfqq
,
800 "resume state: switching off wr");
804 /* make sure weight will be updated, however we got here */
805 bfqq
->entity
.prio_changed
= 1;
810 if (old_wr_coeff
== 1 && bfqq
->wr_coeff
> 1)
811 bfqd
->wr_busy_queues
++;
812 else if (old_wr_coeff
> 1 && bfqq
->wr_coeff
== 1)
813 bfqd
->wr_busy_queues
--;
816 static int bfqq_process_refs(struct bfq_queue
*bfqq
)
818 return bfqq
->ref
- bfqq
->allocated
- bfqq
->entity
.on_st
;
821 /* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */
822 static void bfq_reset_burst_list(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
824 struct bfq_queue
*item
;
825 struct hlist_node
*n
;
827 hlist_for_each_entry_safe(item
, n
, &bfqd
->burst_list
, burst_list_node
)
828 hlist_del_init(&item
->burst_list_node
);
829 hlist_add_head(&bfqq
->burst_list_node
, &bfqd
->burst_list
);
830 bfqd
->burst_size
= 1;
831 bfqd
->burst_parent_entity
= bfqq
->entity
.parent
;
834 /* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */
835 static void bfq_add_to_burst(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
837 /* Increment burst size to take into account also bfqq */
840 if (bfqd
->burst_size
== bfqd
->bfq_large_burst_thresh
) {
841 struct bfq_queue
*pos
, *bfqq_item
;
842 struct hlist_node
*n
;
845 * Enough queues have been activated shortly after each
846 * other to consider this burst as large.
848 bfqd
->large_burst
= true;
851 * We can now mark all queues in the burst list as
852 * belonging to a large burst.
854 hlist_for_each_entry(bfqq_item
, &bfqd
->burst_list
,
856 bfq_mark_bfqq_in_large_burst(bfqq_item
);
857 bfq_mark_bfqq_in_large_burst(bfqq
);
860 * From now on, and until the current burst finishes, any
861 * new queue being activated shortly after the last queue
862 * was inserted in the burst can be immediately marked as
863 * belonging to a large burst. So the burst list is not
864 * needed any more. Remove it.
866 hlist_for_each_entry_safe(pos
, n
, &bfqd
->burst_list
,
868 hlist_del_init(&pos
->burst_list_node
);
870 * Burst not yet large: add bfqq to the burst list. Do
871 * not increment the ref counter for bfqq, because bfqq
872 * is removed from the burst list before freeing bfqq
875 hlist_add_head(&bfqq
->burst_list_node
, &bfqd
->burst_list
);
879 * If many queues belonging to the same group happen to be created
880 * shortly after each other, then the processes associated with these
881 * queues have typically a common goal. In particular, bursts of queue
882 * creations are usually caused by services or applications that spawn
883 * many parallel threads/processes. Examples are systemd during boot,
884 * or git grep. To help these processes get their job done as soon as
885 * possible, it is usually better to not grant either weight-raising
886 * or device idling to their queues.
888 * In this comment we describe, firstly, the reasons why this fact
889 * holds, and, secondly, the next function, which implements the main
890 * steps needed to properly mark these queues so that they can then be
891 * treated in a different way.
893 * The above services or applications benefit mostly from a high
894 * throughput: the quicker the requests of the activated queues are
895 * cumulatively served, the sooner the target job of these queues gets
896 * completed. As a consequence, weight-raising any of these queues,
897 * which also implies idling the device for it, is almost always
898 * counterproductive. In most cases it just lowers throughput.
900 * On the other hand, a burst of queue creations may be caused also by
901 * the start of an application that does not consist of a lot of
902 * parallel I/O-bound threads. In fact, with a complex application,
903 * several short processes may need to be executed to start-up the
904 * application. In this respect, to start an application as quickly as
905 * possible, the best thing to do is in any case to privilege the I/O
906 * related to the application with respect to all other
907 * I/O. Therefore, the best strategy to start as quickly as possible
908 * an application that causes a burst of queue creations is to
909 * weight-raise all the queues created during the burst. This is the
910 * exact opposite of the best strategy for the other type of bursts.
912 * In the end, to take the best action for each of the two cases, the
913 * two types of bursts need to be distinguished. Fortunately, this
914 * seems relatively easy, by looking at the sizes of the bursts. In
915 * particular, we found a threshold such that only bursts with a
916 * larger size than that threshold are apparently caused by
917 * services or commands such as systemd or git grep. For brevity,
918 * hereafter we call just 'large' these bursts. BFQ *does not*
919 * weight-raise queues whose creation occurs in a large burst. In
920 * addition, for each of these queues BFQ performs or does not perform
921 * idling depending on which choice boosts the throughput more. The
922 * exact choice depends on the device and request pattern at
925 * Unfortunately, false positives may occur while an interactive task
926 * is starting (e.g., an application is being started). The
927 * consequence is that the queues associated with the task do not
928 * enjoy weight raising as expected. Fortunately these false positives
929 * are very rare. They typically occur if some service happens to
930 * start doing I/O exactly when the interactive task starts.
932 * Turning back to the next function, it implements all the steps
933 * needed to detect the occurrence of a large burst and to properly
934 * mark all the queues belonging to it (so that they can then be
935 * treated in a different way). This goal is achieved by maintaining a
936 * "burst list" that holds, temporarily, the queues that belong to the
937 * burst in progress. The list is then used to mark these queues as
938 * belonging to a large burst if the burst does become large. The main
939 * steps are the following.
941 * . when the very first queue is created, the queue is inserted into the
942 * list (as it could be the first queue in a possible burst)
944 * . if the current burst has not yet become large, and a queue Q that does
945 * not yet belong to the burst is activated shortly after the last time
946 * at which a new queue entered the burst list, then the function appends
947 * Q to the burst list
949 * . if, as a consequence of the previous step, the burst size reaches
950 * the large-burst threshold, then
952 * . all the queues in the burst list are marked as belonging to a
955 * . the burst list is deleted; in fact, the burst list already served
956 * its purpose (keeping temporarily track of the queues in a burst,
957 * so as to be able to mark them as belonging to a large burst in the
958 * previous sub-step), and now is not needed any more
960 * . the device enters a large-burst mode
962 * . if a queue Q that does not belong to the burst is created while
963 * the device is in large-burst mode and shortly after the last time
964 * at which a queue either entered the burst list or was marked as
965 * belonging to the current large burst, then Q is immediately marked
966 * as belonging to a large burst.
968 * . if a queue Q that does not belong to the burst is created a while
969 * later, i.e., not shortly after, than the last time at which a queue
970 * either entered the burst list or was marked as belonging to the
971 * current large burst, then the current burst is deemed as finished and:
973 * . the large-burst mode is reset if set
975 * . the burst list is emptied
977 * . Q is inserted in the burst list, as Q may be the first queue
978 * in a possible new burst (then the burst list contains just Q
981 static void bfq_handle_burst(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
984 * If bfqq is already in the burst list or is part of a large
985 * burst, or finally has just been split, then there is
986 * nothing else to do.
988 if (!hlist_unhashed(&bfqq
->burst_list_node
) ||
989 bfq_bfqq_in_large_burst(bfqq
) ||
990 time_is_after_eq_jiffies(bfqq
->split_time
+
991 msecs_to_jiffies(10)))
995 * If bfqq's creation happens late enough, or bfqq belongs to
996 * a different group than the burst group, then the current
997 * burst is finished, and related data structures must be
1000 * In this respect, consider the special case where bfqq is
1001 * the very first queue created after BFQ is selected for this
1002 * device. In this case, last_ins_in_burst and
1003 * burst_parent_entity are not yet significant when we get
1004 * here. But it is easy to verify that, whether or not the
1005 * following condition is true, bfqq will end up being
1006 * inserted into the burst list. In particular the list will
1007 * happen to contain only bfqq. And this is exactly what has
1008 * to happen, as bfqq may be the first queue of the first
1011 if (time_is_before_jiffies(bfqd
->last_ins_in_burst
+
1012 bfqd
->bfq_burst_interval
) ||
1013 bfqq
->entity
.parent
!= bfqd
->burst_parent_entity
) {
1014 bfqd
->large_burst
= false;
1015 bfq_reset_burst_list(bfqd
, bfqq
);
1020 * If we get here, then bfqq is being activated shortly after the
1021 * last queue. So, if the current burst is also large, we can mark
1022 * bfqq as belonging to this large burst immediately.
1024 if (bfqd
->large_burst
) {
1025 bfq_mark_bfqq_in_large_burst(bfqq
);
1030 * If we get here, then a large-burst state has not yet been
1031 * reached, but bfqq is being activated shortly after the last
1032 * queue. Then we add bfqq to the burst.
1034 bfq_add_to_burst(bfqd
, bfqq
);
1037 * At this point, bfqq either has been added to the current
1038 * burst or has caused the current burst to terminate and a
1039 * possible new burst to start. In particular, in the second
1040 * case, bfqq has become the first queue in the possible new
1041 * burst. In both cases last_ins_in_burst needs to be moved
1044 bfqd
->last_ins_in_burst
= jiffies
;
1047 static int bfq_bfqq_budget_left(struct bfq_queue
*bfqq
)
1049 struct bfq_entity
*entity
= &bfqq
->entity
;
1051 return entity
->budget
- entity
->service
;
1055 * If enough samples have been computed, return the current max budget
1056 * stored in bfqd, which is dynamically updated according to the
1057 * estimated disk peak rate; otherwise return the default max budget
1059 static int bfq_max_budget(struct bfq_data
*bfqd
)
1061 if (bfqd
->budgets_assigned
< bfq_stats_min_budgets
)
1062 return bfq_default_max_budget
;
1064 return bfqd
->bfq_max_budget
;
1068 * Return min budget, which is a fraction of the current or default
1069 * max budget (trying with 1/32)
1071 static int bfq_min_budget(struct bfq_data
*bfqd
)
1073 if (bfqd
->budgets_assigned
< bfq_stats_min_budgets
)
1074 return bfq_default_max_budget
/ 32;
1076 return bfqd
->bfq_max_budget
/ 32;
1080 * The next function, invoked after the input queue bfqq switches from
1081 * idle to busy, updates the budget of bfqq. The function also tells
1082 * whether the in-service queue should be expired, by returning
1083 * true. The purpose of expiring the in-service queue is to give bfqq
1084 * the chance to possibly preempt the in-service queue, and the reason
1085 * for preempting the in-service queue is to achieve one of the two
1088 * 1. Guarantee to bfqq its reserved bandwidth even if bfqq has
1089 * expired because it has remained idle. In particular, bfqq may have
1090 * expired for one of the following two reasons:
1092 * - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling
1093 * and did not make it to issue a new request before its last
1094 * request was served;
1096 * - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue
1097 * a new request before the expiration of the idling-time.
1099 * Even if bfqq has expired for one of the above reasons, the process
1100 * associated with the queue may be however issuing requests greedily,
1101 * and thus be sensitive to the bandwidth it receives (bfqq may have
1102 * remained idle for other reasons: CPU high load, bfqq not enjoying
1103 * idling, I/O throttling somewhere in the path from the process to
1104 * the I/O scheduler, ...). But if, after every expiration for one of
1105 * the above two reasons, bfqq has to wait for the service of at least
1106 * one full budget of another queue before being served again, then
1107 * bfqq is likely to get a much lower bandwidth or resource time than
1108 * its reserved ones. To address this issue, two countermeasures need
1111 * First, the budget and the timestamps of bfqq need to be updated in
1112 * a special way on bfqq reactivation: they need to be updated as if
1113 * bfqq did not remain idle and did not expire. In fact, if they are
1114 * computed as if bfqq expired and remained idle until reactivation,
1115 * then the process associated with bfqq is treated as if, instead of
1116 * being greedy, it stopped issuing requests when bfqq remained idle,
1117 * and restarts issuing requests only on this reactivation. In other
1118 * words, the scheduler does not help the process recover the "service
1119 * hole" between bfqq expiration and reactivation. As a consequence,
1120 * the process receives a lower bandwidth than its reserved one. In
1121 * contrast, to recover this hole, the budget must be updated as if
1122 * bfqq was not expired at all before this reactivation, i.e., it must
1123 * be set to the value of the remaining budget when bfqq was
1124 * expired. Along the same line, timestamps need to be assigned the
1125 * value they had the last time bfqq was selected for service, i.e.,
1126 * before last expiration. Thus timestamps need to be back-shifted
1127 * with respect to their normal computation (see [1] for more details
1128 * on this tricky aspect).
1130 * Secondly, to allow the process to recover the hole, the in-service
1131 * queue must be expired too, to give bfqq the chance to preempt it
1132 * immediately. In fact, if bfqq has to wait for a full budget of the
1133 * in-service queue to be completed, then it may become impossible to
1134 * let the process recover the hole, even if the back-shifted
1135 * timestamps of bfqq are lower than those of the in-service queue. If
1136 * this happens for most or all of the holes, then the process may not
1137 * receive its reserved bandwidth. In this respect, it is worth noting
1138 * that, being the service of outstanding requests unpreemptible, a
1139 * little fraction of the holes may however be unrecoverable, thereby
1140 * causing a little loss of bandwidth.
1142 * The last important point is detecting whether bfqq does need this
1143 * bandwidth recovery. In this respect, the next function deems the
1144 * process associated with bfqq greedy, and thus allows it to recover
1145 * the hole, if: 1) the process is waiting for the arrival of a new
1146 * request (which implies that bfqq expired for one of the above two
1147 * reasons), and 2) such a request has arrived soon. The first
1148 * condition is controlled through the flag non_blocking_wait_rq,
1149 * while the second through the flag arrived_in_time. If both
1150 * conditions hold, then the function computes the budget in the
1151 * above-described special way, and signals that the in-service queue
1152 * should be expired. Timestamp back-shifting is done later in
1153 * __bfq_activate_entity.
1155 * 2. Reduce latency. Even if timestamps are not backshifted to let
1156 * the process associated with bfqq recover a service hole, bfqq may
1157 * however happen to have, after being (re)activated, a lower finish
1158 * timestamp than the in-service queue. That is, the next budget of
1159 * bfqq may have to be completed before the one of the in-service
1160 * queue. If this is the case, then preempting the in-service queue
1161 * allows this goal to be achieved, apart from the unpreemptible,
1162 * outstanding requests mentioned above.
1164 * Unfortunately, regardless of which of the above two goals one wants
1165 * to achieve, service trees need first to be updated to know whether
1166 * the in-service queue must be preempted. To have service trees
1167 * correctly updated, the in-service queue must be expired and
1168 * rescheduled, and bfqq must be scheduled too. This is one of the
1169 * most costly operations (in future versions, the scheduling
1170 * mechanism may be re-designed in such a way to make it possible to
1171 * know whether preemption is needed without needing to update service
1172 * trees). In addition, queue preemptions almost always cause random
1173 * I/O, and thus loss of throughput. Because of these facts, the next
1174 * function adopts the following simple scheme to avoid both costly
1175 * operations and too frequent preemptions: it requests the expiration
1176 * of the in-service queue (unconditionally) only for queues that need
1177 * to recover a hole, or that either are weight-raised or deserve to
1180 static bool bfq_bfqq_update_budg_for_activation(struct bfq_data
*bfqd
,
1181 struct bfq_queue
*bfqq
,
1182 bool arrived_in_time
,
1183 bool wr_or_deserves_wr
)
1185 struct bfq_entity
*entity
= &bfqq
->entity
;
1187 if (bfq_bfqq_non_blocking_wait_rq(bfqq
) && arrived_in_time
) {
1189 * We do not clear the flag non_blocking_wait_rq here, as
1190 * the latter is used in bfq_activate_bfqq to signal
1191 * that timestamps need to be back-shifted (and is
1192 * cleared right after).
1196 * In next assignment we rely on that either
1197 * entity->service or entity->budget are not updated
1198 * on expiration if bfqq is empty (see
1199 * __bfq_bfqq_recalc_budget). Thus both quantities
1200 * remain unchanged after such an expiration, and the
1201 * following statement therefore assigns to
1202 * entity->budget the remaining budget on such an
1203 * expiration. For clarity, entity->service is not
1204 * updated on expiration in any case, and, in normal
1205 * operation, is reset only when bfqq is selected for
1206 * service (see bfq_get_next_queue).
1208 entity
->budget
= min_t(unsigned long,
1209 bfq_bfqq_budget_left(bfqq
),
1215 entity
->budget
= max_t(unsigned long, bfqq
->max_budget
,
1216 bfq_serv_to_charge(bfqq
->next_rq
, bfqq
));
1217 bfq_clear_bfqq_non_blocking_wait_rq(bfqq
);
1218 return wr_or_deserves_wr
;
1222 * Return the farthest future time instant according to jiffies
1225 static unsigned long bfq_greatest_from_now(void)
1227 return jiffies
+ MAX_JIFFY_OFFSET
;
1231 * Return the farthest past time instant according to jiffies
1234 static unsigned long bfq_smallest_from_now(void)
1236 return jiffies
- MAX_JIFFY_OFFSET
;
1239 static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data
*bfqd
,
1240 struct bfq_queue
*bfqq
,
1241 unsigned int old_wr_coeff
,
1242 bool wr_or_deserves_wr
,
1247 if (old_wr_coeff
== 1 && wr_or_deserves_wr
) {
1248 /* start a weight-raising period */
1250 bfqq
->wr_coeff
= bfqd
->bfq_wr_coeff
;
1251 bfqq
->wr_cur_max_time
= bfq_wr_duration(bfqd
);
1254 * No interactive weight raising in progress
1255 * here: assign minus infinity to
1256 * wr_start_at_switch_to_srt, to make sure
1257 * that, at the end of the soft-real-time
1258 * weight raising periods that is starting
1259 * now, no interactive weight-raising period
1260 * may be wrongly considered as still in
1261 * progress (and thus actually started by
1264 bfqq
->wr_start_at_switch_to_srt
=
1265 bfq_smallest_from_now();
1266 bfqq
->wr_coeff
= bfqd
->bfq_wr_coeff
*
1267 BFQ_SOFTRT_WEIGHT_FACTOR
;
1268 bfqq
->wr_cur_max_time
=
1269 bfqd
->bfq_wr_rt_max_time
;
1273 * If needed, further reduce budget to make sure it is
1274 * close to bfqq's backlog, so as to reduce the
1275 * scheduling-error component due to a too large
1276 * budget. Do not care about throughput consequences,
1277 * but only about latency. Finally, do not assign a
1278 * too small budget either, to avoid increasing
1279 * latency by causing too frequent expirations.
1281 bfqq
->entity
.budget
= min_t(unsigned long,
1282 bfqq
->entity
.budget
,
1283 2 * bfq_min_budget(bfqd
));
1284 } else if (old_wr_coeff
> 1) {
1285 if (interactive
) { /* update wr coeff and duration */
1286 bfqq
->wr_coeff
= bfqd
->bfq_wr_coeff
;
1287 bfqq
->wr_cur_max_time
= bfq_wr_duration(bfqd
);
1288 } else if (in_burst
)
1292 * The application is now or still meeting the
1293 * requirements for being deemed soft rt. We
1294 * can then correctly and safely (re)charge
1295 * the weight-raising duration for the
1296 * application with the weight-raising
1297 * duration for soft rt applications.
1299 * In particular, doing this recharge now, i.e.,
1300 * before the weight-raising period for the
1301 * application finishes, reduces the probability
1302 * of the following negative scenario:
1303 * 1) the weight of a soft rt application is
1304 * raised at startup (as for any newly
1305 * created application),
1306 * 2) since the application is not interactive,
1307 * at a certain time weight-raising is
1308 * stopped for the application,
1309 * 3) at that time the application happens to
1310 * still have pending requests, and hence
1311 * is destined to not have a chance to be
1312 * deemed soft rt before these requests are
1313 * completed (see the comments to the
1314 * function bfq_bfqq_softrt_next_start()
1315 * for details on soft rt detection),
1316 * 4) these pending requests experience a high
1317 * latency because the application is not
1318 * weight-raised while they are pending.
1320 if (bfqq
->wr_cur_max_time
!=
1321 bfqd
->bfq_wr_rt_max_time
) {
1322 bfqq
->wr_start_at_switch_to_srt
=
1323 bfqq
->last_wr_start_finish
;
1325 bfqq
->wr_cur_max_time
=
1326 bfqd
->bfq_wr_rt_max_time
;
1327 bfqq
->wr_coeff
= bfqd
->bfq_wr_coeff
*
1328 BFQ_SOFTRT_WEIGHT_FACTOR
;
1330 bfqq
->last_wr_start_finish
= jiffies
;
1335 static bool bfq_bfqq_idle_for_long_time(struct bfq_data
*bfqd
,
1336 struct bfq_queue
*bfqq
)
1338 return bfqq
->dispatched
== 0 &&
1339 time_is_before_jiffies(
1340 bfqq
->budget_timeout
+
1341 bfqd
->bfq_wr_min_idle_time
);
1344 static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data
*bfqd
,
1345 struct bfq_queue
*bfqq
,
1350 bool soft_rt
, in_burst
, wr_or_deserves_wr
,
1351 bfqq_wants_to_preempt
,
1352 idle_for_long_time
= bfq_bfqq_idle_for_long_time(bfqd
, bfqq
),
1354 * See the comments on
1355 * bfq_bfqq_update_budg_for_activation for
1356 * details on the usage of the next variable.
1358 arrived_in_time
= ktime_get_ns() <=
1359 bfqq
->ttime
.last_end_request
+
1360 bfqd
->bfq_slice_idle
* 3;
1364 * bfqq deserves to be weight-raised if:
1366 * - it does not belong to a large burst,
1367 * - it has been idle for enough time or is soft real-time,
1368 * - is linked to a bfq_io_cq (it is not shared in any sense).
1370 in_burst
= bfq_bfqq_in_large_burst(bfqq
);
1371 soft_rt
= bfqd
->bfq_wr_max_softrt_rate
> 0 &&
1373 time_is_before_jiffies(bfqq
->soft_rt_next_start
);
1374 *interactive
= !in_burst
&& idle_for_long_time
;
1375 wr_or_deserves_wr
= bfqd
->low_latency
&&
1376 (bfqq
->wr_coeff
> 1 ||
1377 (bfq_bfqq_sync(bfqq
) &&
1378 bfqq
->bic
&& (*interactive
|| soft_rt
)));
1381 * Using the last flag, update budget and check whether bfqq
1382 * may want to preempt the in-service queue.
1384 bfqq_wants_to_preempt
=
1385 bfq_bfqq_update_budg_for_activation(bfqd
, bfqq
,
1390 * If bfqq happened to be activated in a burst, but has been
1391 * idle for much more than an interactive queue, then we
1392 * assume that, in the overall I/O initiated in the burst, the
1393 * I/O associated with bfqq is finished. So bfqq does not need
1394 * to be treated as a queue belonging to a burst
1395 * anymore. Accordingly, we reset bfqq's in_large_burst flag
1396 * if set, and remove bfqq from the burst list if it's
1397 * there. We do not decrement burst_size, because the fact
1398 * that bfqq does not need to belong to the burst list any
1399 * more does not invalidate the fact that bfqq was created in
1402 if (likely(!bfq_bfqq_just_created(bfqq
)) &&
1403 idle_for_long_time
&&
1404 time_is_before_jiffies(
1405 bfqq
->budget_timeout
+
1406 msecs_to_jiffies(10000))) {
1407 hlist_del_init(&bfqq
->burst_list_node
);
1408 bfq_clear_bfqq_in_large_burst(bfqq
);
1411 bfq_clear_bfqq_just_created(bfqq
);
1414 if (!bfq_bfqq_IO_bound(bfqq
)) {
1415 if (arrived_in_time
) {
1416 bfqq
->requests_within_timer
++;
1417 if (bfqq
->requests_within_timer
>=
1418 bfqd
->bfq_requests_within_timer
)
1419 bfq_mark_bfqq_IO_bound(bfqq
);
1421 bfqq
->requests_within_timer
= 0;
1424 if (bfqd
->low_latency
) {
1425 if (unlikely(time_is_after_jiffies(bfqq
->split_time
)))
1428 jiffies
- bfqd
->bfq_wr_min_idle_time
- 1;
1430 if (time_is_before_jiffies(bfqq
->split_time
+
1431 bfqd
->bfq_wr_min_idle_time
)) {
1432 bfq_update_bfqq_wr_on_rq_arrival(bfqd
, bfqq
,
1439 if (old_wr_coeff
!= bfqq
->wr_coeff
)
1440 bfqq
->entity
.prio_changed
= 1;
1444 bfqq
->last_idle_bklogged
= jiffies
;
1445 bfqq
->service_from_backlogged
= 0;
1446 bfq_clear_bfqq_softrt_update(bfqq
);
1448 bfq_add_bfqq_busy(bfqd
, bfqq
);
1451 * Expire in-service queue only if preemption may be needed
1452 * for guarantees. In this respect, the function
1453 * next_queue_may_preempt just checks a simple, necessary
1454 * condition, and not a sufficient condition based on
1455 * timestamps. In fact, for the latter condition to be
1456 * evaluated, timestamps would need first to be updated, and
1457 * this operation is quite costly (see the comments on the
1458 * function bfq_bfqq_update_budg_for_activation).
1460 if (bfqd
->in_service_queue
&& bfqq_wants_to_preempt
&&
1461 bfqd
->in_service_queue
->wr_coeff
< bfqq
->wr_coeff
&&
1462 next_queue_may_preempt(bfqd
))
1463 bfq_bfqq_expire(bfqd
, bfqd
->in_service_queue
,
1464 false, BFQQE_PREEMPTED
);
1467 static void bfq_add_request(struct request
*rq
)
1469 struct bfq_queue
*bfqq
= RQ_BFQQ(rq
);
1470 struct bfq_data
*bfqd
= bfqq
->bfqd
;
1471 struct request
*next_rq
, *prev
;
1472 unsigned int old_wr_coeff
= bfqq
->wr_coeff
;
1473 bool interactive
= false;
1475 bfq_log_bfqq(bfqd
, bfqq
, "add_request %d", rq_is_sync(rq
));
1476 bfqq
->queued
[rq_is_sync(rq
)]++;
1479 elv_rb_add(&bfqq
->sort_list
, rq
);
1482 * Check if this request is a better next-serve candidate.
1484 prev
= bfqq
->next_rq
;
1485 next_rq
= bfq_choose_req(bfqd
, bfqq
->next_rq
, rq
, bfqd
->last_position
);
1486 bfqq
->next_rq
= next_rq
;
1489 * Adjust priority tree position, if next_rq changes.
1491 if (prev
!= bfqq
->next_rq
)
1492 bfq_pos_tree_add_move(bfqd
, bfqq
);
1494 if (!bfq_bfqq_busy(bfqq
)) /* switching to busy ... */
1495 bfq_bfqq_handle_idle_busy_switch(bfqd
, bfqq
, old_wr_coeff
,
1498 if (bfqd
->low_latency
&& old_wr_coeff
== 1 && !rq_is_sync(rq
) &&
1499 time_is_before_jiffies(
1500 bfqq
->last_wr_start_finish
+
1501 bfqd
->bfq_wr_min_inter_arr_async
)) {
1502 bfqq
->wr_coeff
= bfqd
->bfq_wr_coeff
;
1503 bfqq
->wr_cur_max_time
= bfq_wr_duration(bfqd
);
1505 bfqd
->wr_busy_queues
++;
1506 bfqq
->entity
.prio_changed
= 1;
1508 if (prev
!= bfqq
->next_rq
)
1509 bfq_updated_next_req(bfqd
, bfqq
);
1513 * Assign jiffies to last_wr_start_finish in the following
1516 * . if bfqq is not going to be weight-raised, because, for
1517 * non weight-raised queues, last_wr_start_finish stores the
1518 * arrival time of the last request; as of now, this piece
1519 * of information is used only for deciding whether to
1520 * weight-raise async queues
1522 * . if bfqq is not weight-raised, because, if bfqq is now
1523 * switching to weight-raised, then last_wr_start_finish
1524 * stores the time when weight-raising starts
1526 * . if bfqq is interactive, because, regardless of whether
1527 * bfqq is currently weight-raised, the weight-raising
1528 * period must start or restart (this case is considered
1529 * separately because it is not detected by the above
1530 * conditions, if bfqq is already weight-raised)
1532 * last_wr_start_finish has to be updated also if bfqq is soft
1533 * real-time, because the weight-raising period is constantly
1534 * restarted on idle-to-busy transitions for these queues, but
1535 * this is already done in bfq_bfqq_handle_idle_busy_switch if
1538 if (bfqd
->low_latency
&&
1539 (old_wr_coeff
== 1 || bfqq
->wr_coeff
== 1 || interactive
))
1540 bfqq
->last_wr_start_finish
= jiffies
;
1543 static struct request
*bfq_find_rq_fmerge(struct bfq_data
*bfqd
,
1545 struct request_queue
*q
)
1547 struct bfq_queue
*bfqq
= bfqd
->bio_bfqq
;
1551 return elv_rb_find(&bfqq
->sort_list
, bio_end_sector(bio
));
1556 static sector_t
get_sdist(sector_t last_pos
, struct request
*rq
)
1559 return abs(blk_rq_pos(rq
) - last_pos
);
1564 #if 0 /* Still not clear if we can do without next two functions */
1565 static void bfq_activate_request(struct request_queue
*q
, struct request
*rq
)
1567 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
1569 bfqd
->rq_in_driver
++;
1572 static void bfq_deactivate_request(struct request_queue
*q
, struct request
*rq
)
1574 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
1576 bfqd
->rq_in_driver
--;
1580 static void bfq_remove_request(struct request_queue
*q
,
1583 struct bfq_queue
*bfqq
= RQ_BFQQ(rq
);
1584 struct bfq_data
*bfqd
= bfqq
->bfqd
;
1585 const int sync
= rq_is_sync(rq
);
1587 if (bfqq
->next_rq
== rq
) {
1588 bfqq
->next_rq
= bfq_find_next_rq(bfqd
, bfqq
, rq
);
1589 bfq_updated_next_req(bfqd
, bfqq
);
1592 if (rq
->queuelist
.prev
!= &rq
->queuelist
)
1593 list_del_init(&rq
->queuelist
);
1594 bfqq
->queued
[sync
]--;
1596 elv_rb_del(&bfqq
->sort_list
, rq
);
1598 elv_rqhash_del(q
, rq
);
1599 if (q
->last_merge
== rq
)
1600 q
->last_merge
= NULL
;
1602 if (RB_EMPTY_ROOT(&bfqq
->sort_list
)) {
1603 bfqq
->next_rq
= NULL
;
1605 if (bfq_bfqq_busy(bfqq
) && bfqq
!= bfqd
->in_service_queue
) {
1606 bfq_del_bfqq_busy(bfqd
, bfqq
, false);
1608 * bfqq emptied. In normal operation, when
1609 * bfqq is empty, bfqq->entity.service and
1610 * bfqq->entity.budget must contain,
1611 * respectively, the service received and the
1612 * budget used last time bfqq emptied. These
1613 * facts do not hold in this case, as at least
1614 * this last removal occurred while bfqq is
1615 * not in service. To avoid inconsistencies,
1616 * reset both bfqq->entity.service and
1617 * bfqq->entity.budget, if bfqq has still a
1618 * process that may issue I/O requests to it.
1620 bfqq
->entity
.budget
= bfqq
->entity
.service
= 0;
1624 * Remove queue from request-position tree as it is empty.
1626 if (bfqq
->pos_root
) {
1627 rb_erase(&bfqq
->pos_node
, bfqq
->pos_root
);
1628 bfqq
->pos_root
= NULL
;
1632 if (rq
->cmd_flags
& REQ_META
)
1633 bfqq
->meta_pending
--;
1637 static bool bfq_bio_merge(struct blk_mq_hw_ctx
*hctx
, struct bio
*bio
)
1639 struct request_queue
*q
= hctx
->queue
;
1640 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
1641 struct request
*free
= NULL
;
1643 * bfq_bic_lookup grabs the queue_lock: invoke it now and
1644 * store its return value for later use, to avoid nesting
1645 * queue_lock inside the bfqd->lock. We assume that the bic
1646 * returned by bfq_bic_lookup does not go away before
1647 * bfqd->lock is taken.
1649 struct bfq_io_cq
*bic
= bfq_bic_lookup(bfqd
, current
->io_context
, q
);
1652 spin_lock_irq(&bfqd
->lock
);
1655 bfqd
->bio_bfqq
= bic_to_bfqq(bic
, op_is_sync(bio
->bi_opf
));
1657 bfqd
->bio_bfqq
= NULL
;
1658 bfqd
->bio_bic
= bic
;
1660 ret
= blk_mq_sched_try_merge(q
, bio
, &free
);
1663 blk_mq_free_request(free
);
1664 spin_unlock_irq(&bfqd
->lock
);
1669 static int bfq_request_merge(struct request_queue
*q
, struct request
**req
,
1672 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
1673 struct request
*__rq
;
1675 __rq
= bfq_find_rq_fmerge(bfqd
, bio
, q
);
1676 if (__rq
&& elv_bio_merge_ok(__rq
, bio
)) {
1678 return ELEVATOR_FRONT_MERGE
;
1681 return ELEVATOR_NO_MERGE
;
1684 static void bfq_request_merged(struct request_queue
*q
, struct request
*req
,
1685 enum elv_merge type
)
1687 if (type
== ELEVATOR_FRONT_MERGE
&&
1688 rb_prev(&req
->rb_node
) &&
1690 blk_rq_pos(container_of(rb_prev(&req
->rb_node
),
1691 struct request
, rb_node
))) {
1692 struct bfq_queue
*bfqq
= RQ_BFQQ(req
);
1693 struct bfq_data
*bfqd
= bfqq
->bfqd
;
1694 struct request
*prev
, *next_rq
;
1696 /* Reposition request in its sort_list */
1697 elv_rb_del(&bfqq
->sort_list
, req
);
1698 elv_rb_add(&bfqq
->sort_list
, req
);
1700 /* Choose next request to be served for bfqq */
1701 prev
= bfqq
->next_rq
;
1702 next_rq
= bfq_choose_req(bfqd
, bfqq
->next_rq
, req
,
1703 bfqd
->last_position
);
1704 bfqq
->next_rq
= next_rq
;
1706 * If next_rq changes, update both the queue's budget to
1707 * fit the new request and the queue's position in its
1710 if (prev
!= bfqq
->next_rq
) {
1711 bfq_updated_next_req(bfqd
, bfqq
);
1712 bfq_pos_tree_add_move(bfqd
, bfqq
);
1717 static void bfq_requests_merged(struct request_queue
*q
, struct request
*rq
,
1718 struct request
*next
)
1720 struct bfq_queue
*bfqq
= RQ_BFQQ(rq
), *next_bfqq
= RQ_BFQQ(next
);
1722 if (!RB_EMPTY_NODE(&rq
->rb_node
))
1724 spin_lock_irq(&bfqq
->bfqd
->lock
);
1727 * If next and rq belong to the same bfq_queue and next is older
1728 * than rq, then reposition rq in the fifo (by substituting next
1729 * with rq). Otherwise, if next and rq belong to different
1730 * bfq_queues, never reposition rq: in fact, we would have to
1731 * reposition it with respect to next's position in its own fifo,
1732 * which would most certainly be too expensive with respect to
1735 if (bfqq
== next_bfqq
&&
1736 !list_empty(&rq
->queuelist
) && !list_empty(&next
->queuelist
) &&
1737 next
->fifo_time
< rq
->fifo_time
) {
1738 list_del_init(&rq
->queuelist
);
1739 list_replace_init(&next
->queuelist
, &rq
->queuelist
);
1740 rq
->fifo_time
= next
->fifo_time
;
1743 if (bfqq
->next_rq
== next
)
1746 bfq_remove_request(q
, next
);
1747 bfqg_stats_update_io_remove(bfqq_group(bfqq
), next
->cmd_flags
);
1749 spin_unlock_irq(&bfqq
->bfqd
->lock
);
1751 bfqg_stats_update_io_merged(bfqq_group(bfqq
), next
->cmd_flags
);
1754 /* Must be called with bfqq != NULL */
1755 static void bfq_bfqq_end_wr(struct bfq_queue
*bfqq
)
1757 if (bfq_bfqq_busy(bfqq
))
1758 bfqq
->bfqd
->wr_busy_queues
--;
1760 bfqq
->wr_cur_max_time
= 0;
1761 bfqq
->last_wr_start_finish
= jiffies
;
1763 * Trigger a weight change on the next invocation of
1764 * __bfq_entity_update_weight_prio.
1766 bfqq
->entity
.prio_changed
= 1;
1769 void bfq_end_wr_async_queues(struct bfq_data
*bfqd
,
1770 struct bfq_group
*bfqg
)
1774 for (i
= 0; i
< 2; i
++)
1775 for (j
= 0; j
< IOPRIO_BE_NR
; j
++)
1776 if (bfqg
->async_bfqq
[i
][j
])
1777 bfq_bfqq_end_wr(bfqg
->async_bfqq
[i
][j
]);
1778 if (bfqg
->async_idle_bfqq
)
1779 bfq_bfqq_end_wr(bfqg
->async_idle_bfqq
);
1782 static void bfq_end_wr(struct bfq_data
*bfqd
)
1784 struct bfq_queue
*bfqq
;
1786 spin_lock_irq(&bfqd
->lock
);
1788 list_for_each_entry(bfqq
, &bfqd
->active_list
, bfqq_list
)
1789 bfq_bfqq_end_wr(bfqq
);
1790 list_for_each_entry(bfqq
, &bfqd
->idle_list
, bfqq_list
)
1791 bfq_bfqq_end_wr(bfqq
);
1792 bfq_end_wr_async(bfqd
);
1794 spin_unlock_irq(&bfqd
->lock
);
1797 static sector_t
bfq_io_struct_pos(void *io_struct
, bool request
)
1800 return blk_rq_pos(io_struct
);
1802 return ((struct bio
*)io_struct
)->bi_iter
.bi_sector
;
1805 static int bfq_rq_close_to_sector(void *io_struct
, bool request
,
1808 return abs(bfq_io_struct_pos(io_struct
, request
) - sector
) <=
1812 static struct bfq_queue
*bfqq_find_close(struct bfq_data
*bfqd
,
1813 struct bfq_queue
*bfqq
,
1816 struct rb_root
*root
= &bfq_bfqq_to_bfqg(bfqq
)->rq_pos_tree
;
1817 struct rb_node
*parent
, *node
;
1818 struct bfq_queue
*__bfqq
;
1820 if (RB_EMPTY_ROOT(root
))
1824 * First, if we find a request starting at the end of the last
1825 * request, choose it.
1827 __bfqq
= bfq_rq_pos_tree_lookup(bfqd
, root
, sector
, &parent
, NULL
);
1832 * If the exact sector wasn't found, the parent of the NULL leaf
1833 * will contain the closest sector (rq_pos_tree sorted by
1834 * next_request position).
1836 __bfqq
= rb_entry(parent
, struct bfq_queue
, pos_node
);
1837 if (bfq_rq_close_to_sector(__bfqq
->next_rq
, true, sector
))
1840 if (blk_rq_pos(__bfqq
->next_rq
) < sector
)
1841 node
= rb_next(&__bfqq
->pos_node
);
1843 node
= rb_prev(&__bfqq
->pos_node
);
1847 __bfqq
= rb_entry(node
, struct bfq_queue
, pos_node
);
1848 if (bfq_rq_close_to_sector(__bfqq
->next_rq
, true, sector
))
1854 static struct bfq_queue
*bfq_find_close_cooperator(struct bfq_data
*bfqd
,
1855 struct bfq_queue
*cur_bfqq
,
1858 struct bfq_queue
*bfqq
;
1861 * We shall notice if some of the queues are cooperating,
1862 * e.g., working closely on the same area of the device. In
1863 * that case, we can group them together and: 1) don't waste
1864 * time idling, and 2) serve the union of their requests in
1865 * the best possible order for throughput.
1867 bfqq
= bfqq_find_close(bfqd
, cur_bfqq
, sector
);
1868 if (!bfqq
|| bfqq
== cur_bfqq
)
1874 static struct bfq_queue
*
1875 bfq_setup_merge(struct bfq_queue
*bfqq
, struct bfq_queue
*new_bfqq
)
1877 int process_refs
, new_process_refs
;
1878 struct bfq_queue
*__bfqq
;
1881 * If there are no process references on the new_bfqq, then it is
1882 * unsafe to follow the ->new_bfqq chain as other bfqq's in the chain
1883 * may have dropped their last reference (not just their last process
1886 if (!bfqq_process_refs(new_bfqq
))
1889 /* Avoid a circular list and skip interim queue merges. */
1890 while ((__bfqq
= new_bfqq
->new_bfqq
)) {
1896 process_refs
= bfqq_process_refs(bfqq
);
1897 new_process_refs
= bfqq_process_refs(new_bfqq
);
1899 * If the process for the bfqq has gone away, there is no
1900 * sense in merging the queues.
1902 if (process_refs
== 0 || new_process_refs
== 0)
1905 bfq_log_bfqq(bfqq
->bfqd
, bfqq
, "scheduling merge with queue %d",
1909 * Merging is just a redirection: the requests of the process
1910 * owning one of the two queues are redirected to the other queue.
1911 * The latter queue, in its turn, is set as shared if this is the
1912 * first time that the requests of some process are redirected to
1915 * We redirect bfqq to new_bfqq and not the opposite, because
1916 * we are in the context of the process owning bfqq, thus we
1917 * have the io_cq of this process. So we can immediately
1918 * configure this io_cq to redirect the requests of the
1919 * process to new_bfqq. In contrast, the io_cq of new_bfqq is
1920 * not available any more (new_bfqq->bic == NULL).
1922 * Anyway, even in case new_bfqq coincides with the in-service
1923 * queue, redirecting requests the in-service queue is the
1924 * best option, as we feed the in-service queue with new
1925 * requests close to the last request served and, by doing so,
1926 * are likely to increase the throughput.
1928 bfqq
->new_bfqq
= new_bfqq
;
1929 new_bfqq
->ref
+= process_refs
;
1933 static bool bfq_may_be_close_cooperator(struct bfq_queue
*bfqq
,
1934 struct bfq_queue
*new_bfqq
)
1936 if (bfq_class_idle(bfqq
) || bfq_class_idle(new_bfqq
) ||
1937 (bfqq
->ioprio_class
!= new_bfqq
->ioprio_class
))
1941 * If either of the queues has already been detected as seeky,
1942 * then merging it with the other queue is unlikely to lead to
1945 if (BFQQ_SEEKY(bfqq
) || BFQQ_SEEKY(new_bfqq
))
1949 * Interleaved I/O is known to be done by (some) applications
1950 * only for reads, so it does not make sense to merge async
1953 if (!bfq_bfqq_sync(bfqq
) || !bfq_bfqq_sync(new_bfqq
))
1960 * If this function returns true, then bfqq cannot be merged. The idea
1961 * is that true cooperation happens very early after processes start
1962 * to do I/O. Usually, late cooperations are just accidental false
1963 * positives. In case bfqq is weight-raised, such false positives
1964 * would evidently degrade latency guarantees for bfqq.
1966 static bool wr_from_too_long(struct bfq_queue
*bfqq
)
1968 return bfqq
->wr_coeff
> 1 &&
1969 time_is_before_jiffies(bfqq
->last_wr_start_finish
+
1970 msecs_to_jiffies(100));
1974 * Attempt to schedule a merge of bfqq with the currently in-service
1975 * queue or with a close queue among the scheduled queues. Return
1976 * NULL if no merge was scheduled, a pointer to the shared bfq_queue
1977 * structure otherwise.
1979 * The OOM queue is not allowed to participate to cooperation: in fact, since
1980 * the requests temporarily redirected to the OOM queue could be redirected
1981 * again to dedicated queues at any time, the state needed to correctly
1982 * handle merging with the OOM queue would be quite complex and expensive
1983 * to maintain. Besides, in such a critical condition as an out of memory,
1984 * the benefits of queue merging may be little relevant, or even negligible.
1986 * Weight-raised queues can be merged only if their weight-raising
1987 * period has just started. In fact cooperating processes are usually
1988 * started together. Thus, with this filter we avoid false positives
1989 * that would jeopardize low-latency guarantees.
1991 * WARNING: queue merging may impair fairness among non-weight raised
1992 * queues, for at least two reasons: 1) the original weight of a
1993 * merged queue may change during the merged state, 2) even being the
1994 * weight the same, a merged queue may be bloated with many more
1995 * requests than the ones produced by its originally-associated
1998 static struct bfq_queue
*
1999 bfq_setup_cooperator(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
,
2000 void *io_struct
, bool request
)
2002 struct bfq_queue
*in_service_bfqq
, *new_bfqq
;
2005 return bfqq
->new_bfqq
;
2008 wr_from_too_long(bfqq
) ||
2009 unlikely(bfqq
== &bfqd
->oom_bfqq
))
2012 /* If there is only one backlogged queue, don't search. */
2013 if (bfqd
->busy_queues
== 1)
2016 in_service_bfqq
= bfqd
->in_service_queue
;
2018 if (!in_service_bfqq
|| in_service_bfqq
== bfqq
2019 || wr_from_too_long(in_service_bfqq
) ||
2020 unlikely(in_service_bfqq
== &bfqd
->oom_bfqq
))
2021 goto check_scheduled
;
2023 if (bfq_rq_close_to_sector(io_struct
, request
, bfqd
->last_position
) &&
2024 bfqq
->entity
.parent
== in_service_bfqq
->entity
.parent
&&
2025 bfq_may_be_close_cooperator(bfqq
, in_service_bfqq
)) {
2026 new_bfqq
= bfq_setup_merge(bfqq
, in_service_bfqq
);
2031 * Check whether there is a cooperator among currently scheduled
2032 * queues. The only thing we need is that the bio/request is not
2033 * NULL, as we need it to establish whether a cooperator exists.
2036 new_bfqq
= bfq_find_close_cooperator(bfqd
, bfqq
,
2037 bfq_io_struct_pos(io_struct
, request
));
2039 if (new_bfqq
&& !wr_from_too_long(new_bfqq
) &&
2040 likely(new_bfqq
!= &bfqd
->oom_bfqq
) &&
2041 bfq_may_be_close_cooperator(bfqq
, new_bfqq
))
2042 return bfq_setup_merge(bfqq
, new_bfqq
);
2047 static void bfq_bfqq_save_state(struct bfq_queue
*bfqq
)
2049 struct bfq_io_cq
*bic
= bfqq
->bic
;
2052 * If !bfqq->bic, the queue is already shared or its requests
2053 * have already been redirected to a shared queue; both idle window
2054 * and weight raising state have already been saved. Do nothing.
2059 bic
->saved_ttime
= bfqq
->ttime
;
2060 bic
->saved_has_short_ttime
= bfq_bfqq_has_short_ttime(bfqq
);
2061 bic
->saved_IO_bound
= bfq_bfqq_IO_bound(bfqq
);
2062 bic
->saved_in_large_burst
= bfq_bfqq_in_large_burst(bfqq
);
2063 bic
->was_in_burst_list
= !hlist_unhashed(&bfqq
->burst_list_node
);
2064 if (unlikely(bfq_bfqq_just_created(bfqq
) &&
2065 !bfq_bfqq_in_large_burst(bfqq
))) {
2067 * bfqq being merged right after being created: bfqq
2068 * would have deserved interactive weight raising, but
2069 * did not make it to be set in a weight-raised state,
2070 * because of this early merge. Store directly the
2071 * weight-raising state that would have been assigned
2072 * to bfqq, so that to avoid that bfqq unjustly fails
2073 * to enjoy weight raising if split soon.
2075 bic
->saved_wr_coeff
= bfqq
->bfqd
->bfq_wr_coeff
;
2076 bic
->saved_wr_cur_max_time
= bfq_wr_duration(bfqq
->bfqd
);
2077 bic
->saved_last_wr_start_finish
= jiffies
;
2079 bic
->saved_wr_coeff
= bfqq
->wr_coeff
;
2080 bic
->saved_wr_start_at_switch_to_srt
=
2081 bfqq
->wr_start_at_switch_to_srt
;
2082 bic
->saved_last_wr_start_finish
= bfqq
->last_wr_start_finish
;
2083 bic
->saved_wr_cur_max_time
= bfqq
->wr_cur_max_time
;
2088 bfq_merge_bfqqs(struct bfq_data
*bfqd
, struct bfq_io_cq
*bic
,
2089 struct bfq_queue
*bfqq
, struct bfq_queue
*new_bfqq
)
2091 bfq_log_bfqq(bfqd
, bfqq
, "merging with queue %lu",
2092 (unsigned long)new_bfqq
->pid
);
2093 /* Save weight raising and idle window of the merged queues */
2094 bfq_bfqq_save_state(bfqq
);
2095 bfq_bfqq_save_state(new_bfqq
);
2096 if (bfq_bfqq_IO_bound(bfqq
))
2097 bfq_mark_bfqq_IO_bound(new_bfqq
);
2098 bfq_clear_bfqq_IO_bound(bfqq
);
2101 * If bfqq is weight-raised, then let new_bfqq inherit
2102 * weight-raising. To reduce false positives, neglect the case
2103 * where bfqq has just been created, but has not yet made it
2104 * to be weight-raised (which may happen because EQM may merge
2105 * bfqq even before bfq_add_request is executed for the first
2106 * time for bfqq). Handling this case would however be very
2107 * easy, thanks to the flag just_created.
2109 if (new_bfqq
->wr_coeff
== 1 && bfqq
->wr_coeff
> 1) {
2110 new_bfqq
->wr_coeff
= bfqq
->wr_coeff
;
2111 new_bfqq
->wr_cur_max_time
= bfqq
->wr_cur_max_time
;
2112 new_bfqq
->last_wr_start_finish
= bfqq
->last_wr_start_finish
;
2113 new_bfqq
->wr_start_at_switch_to_srt
=
2114 bfqq
->wr_start_at_switch_to_srt
;
2115 if (bfq_bfqq_busy(new_bfqq
))
2116 bfqd
->wr_busy_queues
++;
2117 new_bfqq
->entity
.prio_changed
= 1;
2120 if (bfqq
->wr_coeff
> 1) { /* bfqq has given its wr to new_bfqq */
2122 bfqq
->entity
.prio_changed
= 1;
2123 if (bfq_bfqq_busy(bfqq
))
2124 bfqd
->wr_busy_queues
--;
2127 bfq_log_bfqq(bfqd
, new_bfqq
, "merge_bfqqs: wr_busy %d",
2128 bfqd
->wr_busy_queues
);
2131 * Merge queues (that is, let bic redirect its requests to new_bfqq)
2133 bic_set_bfqq(bic
, new_bfqq
, 1);
2134 bfq_mark_bfqq_coop(new_bfqq
);
2136 * new_bfqq now belongs to at least two bics (it is a shared queue):
2137 * set new_bfqq->bic to NULL. bfqq either:
2138 * - does not belong to any bic any more, and hence bfqq->bic must
2139 * be set to NULL, or
2140 * - is a queue whose owning bics have already been redirected to a
2141 * different queue, hence the queue is destined to not belong to
2142 * any bic soon and bfqq->bic is already NULL (therefore the next
2143 * assignment causes no harm).
2145 new_bfqq
->bic
= NULL
;
2147 /* release process reference to bfqq */
2148 bfq_put_queue(bfqq
);
2151 static bool bfq_allow_bio_merge(struct request_queue
*q
, struct request
*rq
,
2154 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
2155 bool is_sync
= op_is_sync(bio
->bi_opf
);
2156 struct bfq_queue
*bfqq
= bfqd
->bio_bfqq
, *new_bfqq
;
2159 * Disallow merge of a sync bio into an async request.
2161 if (is_sync
&& !rq_is_sync(rq
))
2165 * Lookup the bfqq that this bio will be queued with. Allow
2166 * merge only if rq is queued there.
2172 * We take advantage of this function to perform an early merge
2173 * of the queues of possible cooperating processes.
2175 new_bfqq
= bfq_setup_cooperator(bfqd
, bfqq
, bio
, false);
2178 * bic still points to bfqq, then it has not yet been
2179 * redirected to some other bfq_queue, and a queue
2180 * merge beween bfqq and new_bfqq can be safely
2181 * fulfillled, i.e., bic can be redirected to new_bfqq
2182 * and bfqq can be put.
2184 bfq_merge_bfqqs(bfqd
, bfqd
->bio_bic
, bfqq
,
2187 * If we get here, bio will be queued into new_queue,
2188 * so use new_bfqq to decide whether bio and rq can be
2194 * Change also bqfd->bio_bfqq, as
2195 * bfqd->bio_bic now points to new_bfqq, and
2196 * this function may be invoked again (and then may
2197 * use again bqfd->bio_bfqq).
2199 bfqd
->bio_bfqq
= bfqq
;
2202 return bfqq
== RQ_BFQQ(rq
);
2206 * Set the maximum time for the in-service queue to consume its
2207 * budget. This prevents seeky processes from lowering the throughput.
2208 * In practice, a time-slice service scheme is used with seeky
2211 static void bfq_set_budget_timeout(struct bfq_data
*bfqd
,
2212 struct bfq_queue
*bfqq
)
2214 unsigned int timeout_coeff
;
2216 if (bfqq
->wr_cur_max_time
== bfqd
->bfq_wr_rt_max_time
)
2219 timeout_coeff
= bfqq
->entity
.weight
/ bfqq
->entity
.orig_weight
;
2221 bfqd
->last_budget_start
= ktime_get();
2223 bfqq
->budget_timeout
= jiffies
+
2224 bfqd
->bfq_timeout
* timeout_coeff
;
2227 static void __bfq_set_in_service_queue(struct bfq_data
*bfqd
,
2228 struct bfq_queue
*bfqq
)
2231 bfq_clear_bfqq_fifo_expire(bfqq
);
2233 bfqd
->budgets_assigned
= (bfqd
->budgets_assigned
* 7 + 256) / 8;
2235 if (time_is_before_jiffies(bfqq
->last_wr_start_finish
) &&
2236 bfqq
->wr_coeff
> 1 &&
2237 bfqq
->wr_cur_max_time
== bfqd
->bfq_wr_rt_max_time
&&
2238 time_is_before_jiffies(bfqq
->budget_timeout
)) {
2240 * For soft real-time queues, move the start
2241 * of the weight-raising period forward by the
2242 * time the queue has not received any
2243 * service. Otherwise, a relatively long
2244 * service delay is likely to cause the
2245 * weight-raising period of the queue to end,
2246 * because of the short duration of the
2247 * weight-raising period of a soft real-time
2248 * queue. It is worth noting that this move
2249 * is not so dangerous for the other queues,
2250 * because soft real-time queues are not
2253 * To not add a further variable, we use the
2254 * overloaded field budget_timeout to
2255 * determine for how long the queue has not
2256 * received service, i.e., how much time has
2257 * elapsed since the queue expired. However,
2258 * this is a little imprecise, because
2259 * budget_timeout is set to jiffies if bfqq
2260 * not only expires, but also remains with no
2263 if (time_after(bfqq
->budget_timeout
,
2264 bfqq
->last_wr_start_finish
))
2265 bfqq
->last_wr_start_finish
+=
2266 jiffies
- bfqq
->budget_timeout
;
2268 bfqq
->last_wr_start_finish
= jiffies
;
2271 bfq_set_budget_timeout(bfqd
, bfqq
);
2272 bfq_log_bfqq(bfqd
, bfqq
,
2273 "set_in_service_queue, cur-budget = %d",
2274 bfqq
->entity
.budget
);
2277 bfqd
->in_service_queue
= bfqq
;
2281 * Get and set a new queue for service.
2283 static struct bfq_queue
*bfq_set_in_service_queue(struct bfq_data
*bfqd
)
2285 struct bfq_queue
*bfqq
= bfq_get_next_queue(bfqd
);
2287 __bfq_set_in_service_queue(bfqd
, bfqq
);
2291 static void bfq_arm_slice_timer(struct bfq_data
*bfqd
)
2293 struct bfq_queue
*bfqq
= bfqd
->in_service_queue
;
2296 bfq_mark_bfqq_wait_request(bfqq
);
2299 * We don't want to idle for seeks, but we do want to allow
2300 * fair distribution of slice time for a process doing back-to-back
2301 * seeks. So allow a little bit of time for him to submit a new rq.
2303 sl
= bfqd
->bfq_slice_idle
;
2305 * Unless the queue is being weight-raised or the scenario is
2306 * asymmetric, grant only minimum idle time if the queue
2307 * is seeky. A long idling is preserved for a weight-raised
2308 * queue, or, more in general, in an asymmetric scenario,
2309 * because a long idling is needed for guaranteeing to a queue
2310 * its reserved share of the throughput (in particular, it is
2311 * needed if the queue has a higher weight than some other
2314 if (BFQQ_SEEKY(bfqq
) && bfqq
->wr_coeff
== 1 &&
2315 bfq_symmetric_scenario(bfqd
))
2316 sl
= min_t(u64
, sl
, BFQ_MIN_TT
);
2318 bfqd
->last_idling_start
= ktime_get();
2319 hrtimer_start(&bfqd
->idle_slice_timer
, ns_to_ktime(sl
),
2321 bfqg_stats_set_start_idle_time(bfqq_group(bfqq
));
2325 * In autotuning mode, max_budget is dynamically recomputed as the
2326 * amount of sectors transferred in timeout at the estimated peak
2327 * rate. This enables BFQ to utilize a full timeslice with a full
2328 * budget, even if the in-service queue is served at peak rate. And
2329 * this maximises throughput with sequential workloads.
2331 static unsigned long bfq_calc_max_budget(struct bfq_data
*bfqd
)
2333 return (u64
)bfqd
->peak_rate
* USEC_PER_MSEC
*
2334 jiffies_to_msecs(bfqd
->bfq_timeout
)>>BFQ_RATE_SHIFT
;
2338 * Update parameters related to throughput and responsiveness, as a
2339 * function of the estimated peak rate. See comments on
2340 * bfq_calc_max_budget(), and on T_slow and T_fast arrays.
2342 static void update_thr_responsiveness_params(struct bfq_data
*bfqd
)
2344 int dev_type
= blk_queue_nonrot(bfqd
->queue
);
2346 if (bfqd
->bfq_user_max_budget
== 0)
2347 bfqd
->bfq_max_budget
=
2348 bfq_calc_max_budget(bfqd
);
2350 if (bfqd
->device_speed
== BFQ_BFQD_FAST
&&
2351 bfqd
->peak_rate
< device_speed_thresh
[dev_type
]) {
2352 bfqd
->device_speed
= BFQ_BFQD_SLOW
;
2353 bfqd
->RT_prod
= R_slow
[dev_type
] *
2355 } else if (bfqd
->device_speed
== BFQ_BFQD_SLOW
&&
2356 bfqd
->peak_rate
> device_speed_thresh
[dev_type
]) {
2357 bfqd
->device_speed
= BFQ_BFQD_FAST
;
2358 bfqd
->RT_prod
= R_fast
[dev_type
] *
2363 "dev_type %s dev_speed_class = %s (%llu sects/sec), thresh %llu setcs/sec",
2364 dev_type
== 0 ? "ROT" : "NONROT",
2365 bfqd
->device_speed
== BFQ_BFQD_FAST
? "FAST" : "SLOW",
2366 bfqd
->device_speed
== BFQ_BFQD_FAST
?
2367 (USEC_PER_SEC
*(u64
)R_fast
[dev_type
])>>BFQ_RATE_SHIFT
:
2368 (USEC_PER_SEC
*(u64
)R_slow
[dev_type
])>>BFQ_RATE_SHIFT
,
2369 (USEC_PER_SEC
*(u64
)device_speed_thresh
[dev_type
])>>
2373 static void bfq_reset_rate_computation(struct bfq_data
*bfqd
,
2376 if (rq
!= NULL
) { /* new rq dispatch now, reset accordingly */
2377 bfqd
->last_dispatch
= bfqd
->first_dispatch
= ktime_get_ns();
2378 bfqd
->peak_rate_samples
= 1;
2379 bfqd
->sequential_samples
= 0;
2380 bfqd
->tot_sectors_dispatched
= bfqd
->last_rq_max_size
=
2382 } else /* no new rq dispatched, just reset the number of samples */
2383 bfqd
->peak_rate_samples
= 0; /* full re-init on next disp. */
2386 "reset_rate_computation at end, sample %u/%u tot_sects %llu",
2387 bfqd
->peak_rate_samples
, bfqd
->sequential_samples
,
2388 bfqd
->tot_sectors_dispatched
);
2391 static void bfq_update_rate_reset(struct bfq_data
*bfqd
, struct request
*rq
)
2393 u32 rate
, weight
, divisor
;
2396 * For the convergence property to hold (see comments on
2397 * bfq_update_peak_rate()) and for the assessment to be
2398 * reliable, a minimum number of samples must be present, and
2399 * a minimum amount of time must have elapsed. If not so, do
2400 * not compute new rate. Just reset parameters, to get ready
2401 * for a new evaluation attempt.
2403 if (bfqd
->peak_rate_samples
< BFQ_RATE_MIN_SAMPLES
||
2404 bfqd
->delta_from_first
< BFQ_RATE_MIN_INTERVAL
)
2405 goto reset_computation
;
2408 * If a new request completion has occurred after last
2409 * dispatch, then, to approximate the rate at which requests
2410 * have been served by the device, it is more precise to
2411 * extend the observation interval to the last completion.
2413 bfqd
->delta_from_first
=
2414 max_t(u64
, bfqd
->delta_from_first
,
2415 bfqd
->last_completion
- bfqd
->first_dispatch
);
2418 * Rate computed in sects/usec, and not sects/nsec, for
2421 rate
= div64_ul(bfqd
->tot_sectors_dispatched
<<BFQ_RATE_SHIFT
,
2422 div_u64(bfqd
->delta_from_first
, NSEC_PER_USEC
));
2425 * Peak rate not updated if:
2426 * - the percentage of sequential dispatches is below 3/4 of the
2427 * total, and rate is below the current estimated peak rate
2428 * - rate is unreasonably high (> 20M sectors/sec)
2430 if ((bfqd
->sequential_samples
< (3 * bfqd
->peak_rate_samples
)>>2 &&
2431 rate
<= bfqd
->peak_rate
) ||
2432 rate
> 20<<BFQ_RATE_SHIFT
)
2433 goto reset_computation
;
2436 * We have to update the peak rate, at last! To this purpose,
2437 * we use a low-pass filter. We compute the smoothing constant
2438 * of the filter as a function of the 'weight' of the new
2441 * As can be seen in next formulas, we define this weight as a
2442 * quantity proportional to how sequential the workload is,
2443 * and to how long the observation time interval is.
2445 * The weight runs from 0 to 8. The maximum value of the
2446 * weight, 8, yields the minimum value for the smoothing
2447 * constant. At this minimum value for the smoothing constant,
2448 * the measured rate contributes for half of the next value of
2449 * the estimated peak rate.
2451 * So, the first step is to compute the weight as a function
2452 * of how sequential the workload is. Note that the weight
2453 * cannot reach 9, because bfqd->sequential_samples cannot
2454 * become equal to bfqd->peak_rate_samples, which, in its
2455 * turn, holds true because bfqd->sequential_samples is not
2456 * incremented for the first sample.
2458 weight
= (9 * bfqd
->sequential_samples
) / bfqd
->peak_rate_samples
;
2461 * Second step: further refine the weight as a function of the
2462 * duration of the observation interval.
2464 weight
= min_t(u32
, 8,
2465 div_u64(weight
* bfqd
->delta_from_first
,
2466 BFQ_RATE_REF_INTERVAL
));
2469 * Divisor ranging from 10, for minimum weight, to 2, for
2472 divisor
= 10 - weight
;
2475 * Finally, update peak rate:
2477 * peak_rate = peak_rate * (divisor-1) / divisor + rate / divisor
2479 bfqd
->peak_rate
*= divisor
-1;
2480 bfqd
->peak_rate
/= divisor
;
2481 rate
/= divisor
; /* smoothing constant alpha = 1/divisor */
2483 bfqd
->peak_rate
+= rate
;
2484 update_thr_responsiveness_params(bfqd
);
2487 bfq_reset_rate_computation(bfqd
, rq
);
2491 * Update the read/write peak rate (the main quantity used for
2492 * auto-tuning, see update_thr_responsiveness_params()).
2494 * It is not trivial to estimate the peak rate (correctly): because of
2495 * the presence of sw and hw queues between the scheduler and the
2496 * device components that finally serve I/O requests, it is hard to
2497 * say exactly when a given dispatched request is served inside the
2498 * device, and for how long. As a consequence, it is hard to know
2499 * precisely at what rate a given set of requests is actually served
2502 * On the opposite end, the dispatch time of any request is trivially
2503 * available, and, from this piece of information, the "dispatch rate"
2504 * of requests can be immediately computed. So, the idea in the next
2505 * function is to use what is known, namely request dispatch times
2506 * (plus, when useful, request completion times), to estimate what is
2507 * unknown, namely in-device request service rate.
2509 * The main issue is that, because of the above facts, the rate at
2510 * which a certain set of requests is dispatched over a certain time
2511 * interval can vary greatly with respect to the rate at which the
2512 * same requests are then served. But, since the size of any
2513 * intermediate queue is limited, and the service scheme is lossless
2514 * (no request is silently dropped), the following obvious convergence
2515 * property holds: the number of requests dispatched MUST become
2516 * closer and closer to the number of requests completed as the
2517 * observation interval grows. This is the key property used in
2518 * the next function to estimate the peak service rate as a function
2519 * of the observed dispatch rate. The function assumes to be invoked
2520 * on every request dispatch.
2522 static void bfq_update_peak_rate(struct bfq_data
*bfqd
, struct request
*rq
)
2524 u64 now_ns
= ktime_get_ns();
2526 if (bfqd
->peak_rate_samples
== 0) { /* first dispatch */
2527 bfq_log(bfqd
, "update_peak_rate: goto reset, samples %d",
2528 bfqd
->peak_rate_samples
);
2529 bfq_reset_rate_computation(bfqd
, rq
);
2530 goto update_last_values
; /* will add one sample */
2534 * Device idle for very long: the observation interval lasting
2535 * up to this dispatch cannot be a valid observation interval
2536 * for computing a new peak rate (similarly to the late-
2537 * completion event in bfq_completed_request()). Go to
2538 * update_rate_and_reset to have the following three steps
2540 * - close the observation interval at the last (previous)
2541 * request dispatch or completion
2542 * - compute rate, if possible, for that observation interval
2543 * - start a new observation interval with this dispatch
2545 if (now_ns
- bfqd
->last_dispatch
> 100*NSEC_PER_MSEC
&&
2546 bfqd
->rq_in_driver
== 0)
2547 goto update_rate_and_reset
;
2549 /* Update sampling information */
2550 bfqd
->peak_rate_samples
++;
2552 if ((bfqd
->rq_in_driver
> 0 ||
2553 now_ns
- bfqd
->last_completion
< BFQ_MIN_TT
)
2554 && get_sdist(bfqd
->last_position
, rq
) < BFQQ_SEEK_THR
)
2555 bfqd
->sequential_samples
++;
2557 bfqd
->tot_sectors_dispatched
+= blk_rq_sectors(rq
);
2559 /* Reset max observed rq size every 32 dispatches */
2560 if (likely(bfqd
->peak_rate_samples
% 32))
2561 bfqd
->last_rq_max_size
=
2562 max_t(u32
, blk_rq_sectors(rq
), bfqd
->last_rq_max_size
);
2564 bfqd
->last_rq_max_size
= blk_rq_sectors(rq
);
2566 bfqd
->delta_from_first
= now_ns
- bfqd
->first_dispatch
;
2568 /* Target observation interval not yet reached, go on sampling */
2569 if (bfqd
->delta_from_first
< BFQ_RATE_REF_INTERVAL
)
2570 goto update_last_values
;
2572 update_rate_and_reset
:
2573 bfq_update_rate_reset(bfqd
, rq
);
2575 bfqd
->last_position
= blk_rq_pos(rq
) + blk_rq_sectors(rq
);
2576 bfqd
->last_dispatch
= now_ns
;
2580 * Remove request from internal lists.
2582 static void bfq_dispatch_remove(struct request_queue
*q
, struct request
*rq
)
2584 struct bfq_queue
*bfqq
= RQ_BFQQ(rq
);
2587 * For consistency, the next instruction should have been
2588 * executed after removing the request from the queue and
2589 * dispatching it. We execute instead this instruction before
2590 * bfq_remove_request() (and hence introduce a temporary
2591 * inconsistency), for efficiency. In fact, should this
2592 * dispatch occur for a non in-service bfqq, this anticipated
2593 * increment prevents two counters related to bfqq->dispatched
2594 * from risking to be, first, uselessly decremented, and then
2595 * incremented again when the (new) value of bfqq->dispatched
2596 * happens to be taken into account.
2599 bfq_update_peak_rate(q
->elevator
->elevator_data
, rq
);
2601 bfq_remove_request(q
, rq
);
2604 static void __bfq_bfqq_expire(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
2607 * If this bfqq is shared between multiple processes, check
2608 * to make sure that those processes are still issuing I/Os
2609 * within the mean seek distance. If not, it may be time to
2610 * break the queues apart again.
2612 if (bfq_bfqq_coop(bfqq
) && BFQQ_SEEKY(bfqq
))
2613 bfq_mark_bfqq_split_coop(bfqq
);
2615 if (RB_EMPTY_ROOT(&bfqq
->sort_list
)) {
2616 if (bfqq
->dispatched
== 0)
2618 * Overloading budget_timeout field to store
2619 * the time at which the queue remains with no
2620 * backlog and no outstanding request; used by
2621 * the weight-raising mechanism.
2623 bfqq
->budget_timeout
= jiffies
;
2625 bfq_del_bfqq_busy(bfqd
, bfqq
, true);
2627 bfq_requeue_bfqq(bfqd
, bfqq
, true);
2629 * Resort priority tree of potential close cooperators.
2631 bfq_pos_tree_add_move(bfqd
, bfqq
);
2635 * All in-service entities must have been properly deactivated
2636 * or requeued before executing the next function, which
2637 * resets all in-service entites as no more in service.
2639 __bfq_bfqd_reset_in_service(bfqd
);
2643 * __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior.
2644 * @bfqd: device data.
2645 * @bfqq: queue to update.
2646 * @reason: reason for expiration.
2648 * Handle the feedback on @bfqq budget at queue expiration.
2649 * See the body for detailed comments.
2651 static void __bfq_bfqq_recalc_budget(struct bfq_data
*bfqd
,
2652 struct bfq_queue
*bfqq
,
2653 enum bfqq_expiration reason
)
2655 struct request
*next_rq
;
2656 int budget
, min_budget
;
2658 min_budget
= bfq_min_budget(bfqd
);
2660 if (bfqq
->wr_coeff
== 1)
2661 budget
= bfqq
->max_budget
;
2663 * Use a constant, low budget for weight-raised queues,
2664 * to help achieve a low latency. Keep it slightly higher
2665 * than the minimum possible budget, to cause a little
2666 * bit fewer expirations.
2668 budget
= 2 * min_budget
;
2670 bfq_log_bfqq(bfqd
, bfqq
, "recalc_budg: last budg %d, budg left %d",
2671 bfqq
->entity
.budget
, bfq_bfqq_budget_left(bfqq
));
2672 bfq_log_bfqq(bfqd
, bfqq
, "recalc_budg: last max_budg %d, min budg %d",
2673 budget
, bfq_min_budget(bfqd
));
2674 bfq_log_bfqq(bfqd
, bfqq
, "recalc_budg: sync %d, seeky %d",
2675 bfq_bfqq_sync(bfqq
), BFQQ_SEEKY(bfqd
->in_service_queue
));
2677 if (bfq_bfqq_sync(bfqq
) && bfqq
->wr_coeff
== 1) {
2680 * Caveat: in all the following cases we trade latency
2683 case BFQQE_TOO_IDLE
:
2685 * This is the only case where we may reduce
2686 * the budget: if there is no request of the
2687 * process still waiting for completion, then
2688 * we assume (tentatively) that the timer has
2689 * expired because the batch of requests of
2690 * the process could have been served with a
2691 * smaller budget. Hence, betting that
2692 * process will behave in the same way when it
2693 * becomes backlogged again, we reduce its
2694 * next budget. As long as we guess right,
2695 * this budget cut reduces the latency
2696 * experienced by the process.
2698 * However, if there are still outstanding
2699 * requests, then the process may have not yet
2700 * issued its next request just because it is
2701 * still waiting for the completion of some of
2702 * the still outstanding ones. So in this
2703 * subcase we do not reduce its budget, on the
2704 * contrary we increase it to possibly boost
2705 * the throughput, as discussed in the
2706 * comments to the BUDGET_TIMEOUT case.
2708 if (bfqq
->dispatched
> 0) /* still outstanding reqs */
2709 budget
= min(budget
* 2, bfqd
->bfq_max_budget
);
2711 if (budget
> 5 * min_budget
)
2712 budget
-= 4 * min_budget
;
2714 budget
= min_budget
;
2717 case BFQQE_BUDGET_TIMEOUT
:
2719 * We double the budget here because it gives
2720 * the chance to boost the throughput if this
2721 * is not a seeky process (and has bumped into
2722 * this timeout because of, e.g., ZBR).
2724 budget
= min(budget
* 2, bfqd
->bfq_max_budget
);
2726 case BFQQE_BUDGET_EXHAUSTED
:
2728 * The process still has backlog, and did not
2729 * let either the budget timeout or the disk
2730 * idling timeout expire. Hence it is not
2731 * seeky, has a short thinktime and may be
2732 * happy with a higher budget too. So
2733 * definitely increase the budget of this good
2734 * candidate to boost the disk throughput.
2736 budget
= min(budget
* 4, bfqd
->bfq_max_budget
);
2738 case BFQQE_NO_MORE_REQUESTS
:
2740 * For queues that expire for this reason, it
2741 * is particularly important to keep the
2742 * budget close to the actual service they
2743 * need. Doing so reduces the timestamp
2744 * misalignment problem described in the
2745 * comments in the body of
2746 * __bfq_activate_entity. In fact, suppose
2747 * that a queue systematically expires for
2748 * BFQQE_NO_MORE_REQUESTS and presents a
2749 * new request in time to enjoy timestamp
2750 * back-shifting. The larger the budget of the
2751 * queue is with respect to the service the
2752 * queue actually requests in each service
2753 * slot, the more times the queue can be
2754 * reactivated with the same virtual finish
2755 * time. It follows that, even if this finish
2756 * time is pushed to the system virtual time
2757 * to reduce the consequent timestamp
2758 * misalignment, the queue unjustly enjoys for
2759 * many re-activations a lower finish time
2760 * than all newly activated queues.
2762 * The service needed by bfqq is measured
2763 * quite precisely by bfqq->entity.service.
2764 * Since bfqq does not enjoy device idling,
2765 * bfqq->entity.service is equal to the number
2766 * of sectors that the process associated with
2767 * bfqq requested to read/write before waiting
2768 * for request completions, or blocking for
2771 budget
= max_t(int, bfqq
->entity
.service
, min_budget
);
2776 } else if (!bfq_bfqq_sync(bfqq
)) {
2778 * Async queues get always the maximum possible
2779 * budget, as for them we do not care about latency
2780 * (in addition, their ability to dispatch is limited
2781 * by the charging factor).
2783 budget
= bfqd
->bfq_max_budget
;
2786 bfqq
->max_budget
= budget
;
2788 if (bfqd
->budgets_assigned
>= bfq_stats_min_budgets
&&
2789 !bfqd
->bfq_user_max_budget
)
2790 bfqq
->max_budget
= min(bfqq
->max_budget
, bfqd
->bfq_max_budget
);
2793 * If there is still backlog, then assign a new budget, making
2794 * sure that it is large enough for the next request. Since
2795 * the finish time of bfqq must be kept in sync with the
2796 * budget, be sure to call __bfq_bfqq_expire() *after* this
2799 * If there is no backlog, then no need to update the budget;
2800 * it will be updated on the arrival of a new request.
2802 next_rq
= bfqq
->next_rq
;
2804 bfqq
->entity
.budget
= max_t(unsigned long, bfqq
->max_budget
,
2805 bfq_serv_to_charge(next_rq
, bfqq
));
2807 bfq_log_bfqq(bfqd
, bfqq
, "head sect: %u, new budget %d",
2808 next_rq
? blk_rq_sectors(next_rq
) : 0,
2809 bfqq
->entity
.budget
);
2813 * Return true if the process associated with bfqq is "slow". The slow
2814 * flag is used, in addition to the budget timeout, to reduce the
2815 * amount of service provided to seeky processes, and thus reduce
2816 * their chances to lower the throughput. More details in the comments
2817 * on the function bfq_bfqq_expire().
2819 * An important observation is in order: as discussed in the comments
2820 * on the function bfq_update_peak_rate(), with devices with internal
2821 * queues, it is hard if ever possible to know when and for how long
2822 * an I/O request is processed by the device (apart from the trivial
2823 * I/O pattern where a new request is dispatched only after the
2824 * previous one has been completed). This makes it hard to evaluate
2825 * the real rate at which the I/O requests of each bfq_queue are
2826 * served. In fact, for an I/O scheduler like BFQ, serving a
2827 * bfq_queue means just dispatching its requests during its service
2828 * slot (i.e., until the budget of the queue is exhausted, or the
2829 * queue remains idle, or, finally, a timeout fires). But, during the
2830 * service slot of a bfq_queue, around 100 ms at most, the device may
2831 * be even still processing requests of bfq_queues served in previous
2832 * service slots. On the opposite end, the requests of the in-service
2833 * bfq_queue may be completed after the service slot of the queue
2836 * Anyway, unless more sophisticated solutions are used
2837 * (where possible), the sum of the sizes of the requests dispatched
2838 * during the service slot of a bfq_queue is probably the only
2839 * approximation available for the service received by the bfq_queue
2840 * during its service slot. And this sum is the quantity used in this
2841 * function to evaluate the I/O speed of a process.
2843 static bool bfq_bfqq_is_slow(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
,
2844 bool compensate
, enum bfqq_expiration reason
,
2845 unsigned long *delta_ms
)
2847 ktime_t delta_ktime
;
2849 bool slow
= BFQQ_SEEKY(bfqq
); /* if delta too short, use seekyness */
2851 if (!bfq_bfqq_sync(bfqq
))
2855 delta_ktime
= bfqd
->last_idling_start
;
2857 delta_ktime
= ktime_get();
2858 delta_ktime
= ktime_sub(delta_ktime
, bfqd
->last_budget_start
);
2859 delta_usecs
= ktime_to_us(delta_ktime
);
2861 /* don't use too short time intervals */
2862 if (delta_usecs
< 1000) {
2863 if (blk_queue_nonrot(bfqd
->queue
))
2865 * give same worst-case guarantees as idling
2868 *delta_ms
= BFQ_MIN_TT
/ NSEC_PER_MSEC
;
2869 else /* charge at least one seek */
2870 *delta_ms
= bfq_slice_idle
/ NSEC_PER_MSEC
;
2875 *delta_ms
= delta_usecs
/ USEC_PER_MSEC
;
2878 * Use only long (> 20ms) intervals to filter out excessive
2879 * spikes in service rate estimation.
2881 if (delta_usecs
> 20000) {
2883 * Caveat for rotational devices: processes doing I/O
2884 * in the slower disk zones tend to be slow(er) even
2885 * if not seeky. In this respect, the estimated peak
2886 * rate is likely to be an average over the disk
2887 * surface. Accordingly, to not be too harsh with
2888 * unlucky processes, a process is deemed slow only if
2889 * its rate has been lower than half of the estimated
2892 slow
= bfqq
->entity
.service
< bfqd
->bfq_max_budget
/ 2;
2895 bfq_log_bfqq(bfqd
, bfqq
, "bfq_bfqq_is_slow: slow %d", slow
);
2901 * To be deemed as soft real-time, an application must meet two
2902 * requirements. First, the application must not require an average
2903 * bandwidth higher than the approximate bandwidth required to playback or
2904 * record a compressed high-definition video.
2905 * The next function is invoked on the completion of the last request of a
2906 * batch, to compute the next-start time instant, soft_rt_next_start, such
2907 * that, if the next request of the application does not arrive before
2908 * soft_rt_next_start, then the above requirement on the bandwidth is met.
2910 * The second requirement is that the request pattern of the application is
2911 * isochronous, i.e., that, after issuing a request or a batch of requests,
2912 * the application stops issuing new requests until all its pending requests
2913 * have been completed. After that, the application may issue a new batch,
2915 * For this reason the next function is invoked to compute
2916 * soft_rt_next_start only for applications that meet this requirement,
2917 * whereas soft_rt_next_start is set to infinity for applications that do
2920 * Unfortunately, even a greedy application may happen to behave in an
2921 * isochronous way if the CPU load is high. In fact, the application may
2922 * stop issuing requests while the CPUs are busy serving other processes,
2923 * then restart, then stop again for a while, and so on. In addition, if
2924 * the disk achieves a low enough throughput with the request pattern
2925 * issued by the application (e.g., because the request pattern is random
2926 * and/or the device is slow), then the application may meet the above
2927 * bandwidth requirement too. To prevent such a greedy application to be
2928 * deemed as soft real-time, a further rule is used in the computation of
2929 * soft_rt_next_start: soft_rt_next_start must be higher than the current
2930 * time plus the maximum time for which the arrival of a request is waited
2931 * for when a sync queue becomes idle, namely bfqd->bfq_slice_idle.
2932 * This filters out greedy applications, as the latter issue instead their
2933 * next request as soon as possible after the last one has been completed
2934 * (in contrast, when a batch of requests is completed, a soft real-time
2935 * application spends some time processing data).
2937 * Unfortunately, the last filter may easily generate false positives if
2938 * only bfqd->bfq_slice_idle is used as a reference time interval and one
2939 * or both the following cases occur:
2940 * 1) HZ is so low that the duration of a jiffy is comparable to or higher
2941 * than bfqd->bfq_slice_idle. This happens, e.g., on slow devices with
2943 * 2) jiffies, instead of increasing at a constant rate, may stop increasing
2944 * for a while, then suddenly 'jump' by several units to recover the lost
2945 * increments. This seems to happen, e.g., inside virtual machines.
2946 * To address this issue, we do not use as a reference time interval just
2947 * bfqd->bfq_slice_idle, but bfqd->bfq_slice_idle plus a few jiffies. In
2948 * particular we add the minimum number of jiffies for which the filter
2949 * seems to be quite precise also in embedded systems and KVM/QEMU virtual
2952 static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data
*bfqd
,
2953 struct bfq_queue
*bfqq
)
2955 return max(bfqq
->last_idle_bklogged
+
2956 HZ
* bfqq
->service_from_backlogged
/
2957 bfqd
->bfq_wr_max_softrt_rate
,
2958 jiffies
+ nsecs_to_jiffies(bfqq
->bfqd
->bfq_slice_idle
) + 4);
2962 * bfq_bfqq_expire - expire a queue.
2963 * @bfqd: device owning the queue.
2964 * @bfqq: the queue to expire.
2965 * @compensate: if true, compensate for the time spent idling.
2966 * @reason: the reason causing the expiration.
2968 * If the process associated with bfqq does slow I/O (e.g., because it
2969 * issues random requests), we charge bfqq with the time it has been
2970 * in service instead of the service it has received (see
2971 * bfq_bfqq_charge_time for details on how this goal is achieved). As
2972 * a consequence, bfqq will typically get higher timestamps upon
2973 * reactivation, and hence it will be rescheduled as if it had
2974 * received more service than what it has actually received. In the
2975 * end, bfqq receives less service in proportion to how slowly its
2976 * associated process consumes its budgets (and hence how seriously it
2977 * tends to lower the throughput). In addition, this time-charging
2978 * strategy guarantees time fairness among slow processes. In
2979 * contrast, if the process associated with bfqq is not slow, we
2980 * charge bfqq exactly with the service it has received.
2982 * Charging time to the first type of queues and the exact service to
2983 * the other has the effect of using the WF2Q+ policy to schedule the
2984 * former on a timeslice basis, without violating service domain
2985 * guarantees among the latter.
2987 void bfq_bfqq_expire(struct bfq_data
*bfqd
,
2988 struct bfq_queue
*bfqq
,
2990 enum bfqq_expiration reason
)
2993 unsigned long delta
= 0;
2994 struct bfq_entity
*entity
= &bfqq
->entity
;
2998 * Check whether the process is slow (see bfq_bfqq_is_slow).
3000 slow
= bfq_bfqq_is_slow(bfqd
, bfqq
, compensate
, reason
, &delta
);
3003 * Increase service_from_backlogged before next statement,
3004 * because the possible next invocation of
3005 * bfq_bfqq_charge_time would likely inflate
3006 * entity->service. In contrast, service_from_backlogged must
3007 * contain real service, to enable the soft real-time
3008 * heuristic to correctly compute the bandwidth consumed by
3011 bfqq
->service_from_backlogged
+= entity
->service
;
3014 * As above explained, charge slow (typically seeky) and
3015 * timed-out queues with the time and not the service
3016 * received, to favor sequential workloads.
3018 * Processes doing I/O in the slower disk zones will tend to
3019 * be slow(er) even if not seeky. Therefore, since the
3020 * estimated peak rate is actually an average over the disk
3021 * surface, these processes may timeout just for bad luck. To
3022 * avoid punishing them, do not charge time to processes that
3023 * succeeded in consuming at least 2/3 of their budget. This
3024 * allows BFQ to preserve enough elasticity to still perform
3025 * bandwidth, and not time, distribution with little unlucky
3026 * or quasi-sequential processes.
3028 if (bfqq
->wr_coeff
== 1 &&
3030 (reason
== BFQQE_BUDGET_TIMEOUT
&&
3031 bfq_bfqq_budget_left(bfqq
) >= entity
->budget
/ 3)))
3032 bfq_bfqq_charge_time(bfqd
, bfqq
, delta
);
3034 if (reason
== BFQQE_TOO_IDLE
&&
3035 entity
->service
<= 2 * entity
->budget
/ 10)
3036 bfq_clear_bfqq_IO_bound(bfqq
);
3038 if (bfqd
->low_latency
&& bfqq
->wr_coeff
== 1)
3039 bfqq
->last_wr_start_finish
= jiffies
;
3041 if (bfqd
->low_latency
&& bfqd
->bfq_wr_max_softrt_rate
> 0 &&
3042 RB_EMPTY_ROOT(&bfqq
->sort_list
)) {
3044 * If we get here, and there are no outstanding
3045 * requests, then the request pattern is isochronous
3046 * (see the comments on the function
3047 * bfq_bfqq_softrt_next_start()). Thus we can compute
3048 * soft_rt_next_start. If, instead, the queue still
3049 * has outstanding requests, then we have to wait for
3050 * the completion of all the outstanding requests to
3051 * discover whether the request pattern is actually
3054 if (bfqq
->dispatched
== 0)
3055 bfqq
->soft_rt_next_start
=
3056 bfq_bfqq_softrt_next_start(bfqd
, bfqq
);
3059 * The application is still waiting for the
3060 * completion of one or more requests:
3061 * prevent it from possibly being incorrectly
3062 * deemed as soft real-time by setting its
3063 * soft_rt_next_start to infinity. In fact,
3064 * without this assignment, the application
3065 * would be incorrectly deemed as soft
3067 * 1) it issued a new request before the
3068 * completion of all its in-flight
3070 * 2) at that time, its soft_rt_next_start
3071 * happened to be in the past.
3073 bfqq
->soft_rt_next_start
=
3074 bfq_greatest_from_now();
3076 * Schedule an update of soft_rt_next_start to when
3077 * the task may be discovered to be isochronous.
3079 bfq_mark_bfqq_softrt_update(bfqq
);
3083 bfq_log_bfqq(bfqd
, bfqq
,
3084 "expire (%d, slow %d, num_disp %d, short_ttime %d)", reason
,
3085 slow
, bfqq
->dispatched
, bfq_bfqq_has_short_ttime(bfqq
));
3088 * Increase, decrease or leave budget unchanged according to
3091 __bfq_bfqq_recalc_budget(bfqd
, bfqq
, reason
);
3093 __bfq_bfqq_expire(bfqd
, bfqq
);
3095 /* mark bfqq as waiting a request only if a bic still points to it */
3096 if (ref
> 1 && !bfq_bfqq_busy(bfqq
) &&
3097 reason
!= BFQQE_BUDGET_TIMEOUT
&&
3098 reason
!= BFQQE_BUDGET_EXHAUSTED
)
3099 bfq_mark_bfqq_non_blocking_wait_rq(bfqq
);
3103 * Budget timeout is not implemented through a dedicated timer, but
3104 * just checked on request arrivals and completions, as well as on
3105 * idle timer expirations.
3107 static bool bfq_bfqq_budget_timeout(struct bfq_queue
*bfqq
)
3109 return time_is_before_eq_jiffies(bfqq
->budget_timeout
);
3113 * If we expire a queue that is actively waiting (i.e., with the
3114 * device idled) for the arrival of a new request, then we may incur
3115 * the timestamp misalignment problem described in the body of the
3116 * function __bfq_activate_entity. Hence we return true only if this
3117 * condition does not hold, or if the queue is slow enough to deserve
3118 * only to be kicked off for preserving a high throughput.
3120 static bool bfq_may_expire_for_budg_timeout(struct bfq_queue
*bfqq
)
3122 bfq_log_bfqq(bfqq
->bfqd
, bfqq
,
3123 "may_budget_timeout: wait_request %d left %d timeout %d",
3124 bfq_bfqq_wait_request(bfqq
),
3125 bfq_bfqq_budget_left(bfqq
) >= bfqq
->entity
.budget
/ 3,
3126 bfq_bfqq_budget_timeout(bfqq
));
3128 return (!bfq_bfqq_wait_request(bfqq
) ||
3129 bfq_bfqq_budget_left(bfqq
) >= bfqq
->entity
.budget
/ 3)
3131 bfq_bfqq_budget_timeout(bfqq
);
3135 * For a queue that becomes empty, device idling is allowed only if
3136 * this function returns true for the queue. As a consequence, since
3137 * device idling plays a critical role in both throughput boosting and
3138 * service guarantees, the return value of this function plays a
3139 * critical role in both these aspects as well.
3141 * In a nutshell, this function returns true only if idling is
3142 * beneficial for throughput or, even if detrimental for throughput,
3143 * idling is however necessary to preserve service guarantees (low
3144 * latency, desired throughput distribution, ...). In particular, on
3145 * NCQ-capable devices, this function tries to return false, so as to
3146 * help keep the drives' internal queues full, whenever this helps the
3147 * device boost the throughput without causing any service-guarantee
3150 * In more detail, the return value of this function is obtained by,
3151 * first, computing a number of boolean variables that take into
3152 * account throughput and service-guarantee issues, and, then,
3153 * combining these variables in a logical expression. Most of the
3154 * issues taken into account are not trivial. We discuss these issues
3155 * individually while introducing the variables.
3157 static bool bfq_bfqq_may_idle(struct bfq_queue
*bfqq
)
3159 struct bfq_data
*bfqd
= bfqq
->bfqd
;
3160 bool rot_without_queueing
=
3161 !blk_queue_nonrot(bfqd
->queue
) && !bfqd
->hw_tag
,
3162 bfqq_sequential_and_IO_bound
,
3163 idling_boosts_thr
, idling_boosts_thr_without_issues
,
3164 idling_needed_for_service_guarantees
,
3165 asymmetric_scenario
;
3167 if (bfqd
->strict_guarantees
)
3171 * Idling is performed only if slice_idle > 0. In addition, we
3174 * (b) bfqq is in the idle io prio class: in this case we do
3175 * not idle because we want to minimize the bandwidth that
3176 * queues in this class can steal to higher-priority queues
3178 if (bfqd
->bfq_slice_idle
== 0 || !bfq_bfqq_sync(bfqq
) ||
3179 bfq_class_idle(bfqq
))
3182 bfqq_sequential_and_IO_bound
= !BFQQ_SEEKY(bfqq
) &&
3183 bfq_bfqq_IO_bound(bfqq
) && bfq_bfqq_has_short_ttime(bfqq
);
3186 * The next variable takes into account the cases where idling
3187 * boosts the throughput.
3189 * The value of the variable is computed considering, first, that
3190 * idling is virtually always beneficial for the throughput if:
3191 * (a) the device is not NCQ-capable and rotational, or
3192 * (b) regardless of the presence of NCQ, the device is rotational and
3193 * the request pattern for bfqq is I/O-bound and sequential, or
3194 * (c) regardless of whether it is rotational, the device is
3195 * not NCQ-capable and the request pattern for bfqq is
3196 * I/O-bound and sequential.
3198 * Secondly, and in contrast to the above item (b), idling an
3199 * NCQ-capable flash-based device would not boost the
3200 * throughput even with sequential I/O; rather it would lower
3201 * the throughput in proportion to how fast the device
3202 * is. Accordingly, the next variable is true if any of the
3203 * above conditions (a), (b) or (c) is true, and, in
3204 * particular, happens to be false if bfqd is an NCQ-capable
3205 * flash-based device.
3207 idling_boosts_thr
= rot_without_queueing
||
3208 ((!blk_queue_nonrot(bfqd
->queue
) || !bfqd
->hw_tag
) &&
3209 bfqq_sequential_and_IO_bound
);
3212 * The value of the next variable,
3213 * idling_boosts_thr_without_issues, is equal to that of
3214 * idling_boosts_thr, unless a special case holds. In this
3215 * special case, described below, idling may cause problems to
3216 * weight-raised queues.
3218 * When the request pool is saturated (e.g., in the presence
3219 * of write hogs), if the processes associated with
3220 * non-weight-raised queues ask for requests at a lower rate,
3221 * then processes associated with weight-raised queues have a
3222 * higher probability to get a request from the pool
3223 * immediately (or at least soon) when they need one. Thus
3224 * they have a higher probability to actually get a fraction
3225 * of the device throughput proportional to their high
3226 * weight. This is especially true with NCQ-capable drives,
3227 * which enqueue several requests in advance, and further
3228 * reorder internally-queued requests.
3230 * For this reason, we force to false the value of
3231 * idling_boosts_thr_without_issues if there are weight-raised
3232 * busy queues. In this case, and if bfqq is not weight-raised,
3233 * this guarantees that the device is not idled for bfqq (if,
3234 * instead, bfqq is weight-raised, then idling will be
3235 * guaranteed by another variable, see below). Combined with
3236 * the timestamping rules of BFQ (see [1] for details), this
3237 * behavior causes bfqq, and hence any sync non-weight-raised
3238 * queue, to get a lower number of requests served, and thus
3239 * to ask for a lower number of requests from the request
3240 * pool, before the busy weight-raised queues get served
3241 * again. This often mitigates starvation problems in the
3242 * presence of heavy write workloads and NCQ, thereby
3243 * guaranteeing a higher application and system responsiveness
3244 * in these hostile scenarios.
3246 idling_boosts_thr_without_issues
= idling_boosts_thr
&&
3247 bfqd
->wr_busy_queues
== 0;
3250 * There is then a case where idling must be performed not
3251 * for throughput concerns, but to preserve service
3254 * To introduce this case, we can note that allowing the drive
3255 * to enqueue more than one request at a time, and hence
3256 * delegating de facto final scheduling decisions to the
3257 * drive's internal scheduler, entails loss of control on the
3258 * actual request service order. In particular, the critical
3259 * situation is when requests from different processes happen
3260 * to be present, at the same time, in the internal queue(s)
3261 * of the drive. In such a situation, the drive, by deciding
3262 * the service order of the internally-queued requests, does
3263 * determine also the actual throughput distribution among
3264 * these processes. But the drive typically has no notion or
3265 * concern about per-process throughput distribution, and
3266 * makes its decisions only on a per-request basis. Therefore,
3267 * the service distribution enforced by the drive's internal
3268 * scheduler is likely to coincide with the desired
3269 * device-throughput distribution only in a completely
3270 * symmetric scenario where:
3271 * (i) each of these processes must get the same throughput as
3273 * (ii) all these processes have the same I/O pattern
3274 (either sequential or random).
3275 * In fact, in such a scenario, the drive will tend to treat
3276 * the requests of each of these processes in about the same
3277 * way as the requests of the others, and thus to provide
3278 * each of these processes with about the same throughput
3279 * (which is exactly the desired throughput distribution). In
3280 * contrast, in any asymmetric scenario, device idling is
3281 * certainly needed to guarantee that bfqq receives its
3282 * assigned fraction of the device throughput (see [1] for
3285 * We address this issue by controlling, actually, only the
3286 * symmetry sub-condition (i), i.e., provided that
3287 * sub-condition (i) holds, idling is not performed,
3288 * regardless of whether sub-condition (ii) holds. In other
3289 * words, only if sub-condition (i) holds, then idling is
3290 * allowed, and the device tends to be prevented from queueing
3291 * many requests, possibly of several processes. The reason
3292 * for not controlling also sub-condition (ii) is that we
3293 * exploit preemption to preserve guarantees in case of
3294 * symmetric scenarios, even if (ii) does not hold, as
3295 * explained in the next two paragraphs.
3297 * Even if a queue, say Q, is expired when it remains idle, Q
3298 * can still preempt the new in-service queue if the next
3299 * request of Q arrives soon (see the comments on
3300 * bfq_bfqq_update_budg_for_activation). If all queues and
3301 * groups have the same weight, this form of preemption,
3302 * combined with the hole-recovery heuristic described in the
3303 * comments on function bfq_bfqq_update_budg_for_activation,
3304 * are enough to preserve a correct bandwidth distribution in
3305 * the mid term, even without idling. In fact, even if not
3306 * idling allows the internal queues of the device to contain
3307 * many requests, and thus to reorder requests, we can rather
3308 * safely assume that the internal scheduler still preserves a
3309 * minimum of mid-term fairness. The motivation for using
3310 * preemption instead of idling is that, by not idling,
3311 * service guarantees are preserved without minimally
3312 * sacrificing throughput. In other words, both a high
3313 * throughput and its desired distribution are obtained.
3315 * More precisely, this preemption-based, idleless approach
3316 * provides fairness in terms of IOPS, and not sectors per
3317 * second. This can be seen with a simple example. Suppose
3318 * that there are two queues with the same weight, but that
3319 * the first queue receives requests of 8 sectors, while the
3320 * second queue receives requests of 1024 sectors. In
3321 * addition, suppose that each of the two queues contains at
3322 * most one request at a time, which implies that each queue
3323 * always remains idle after it is served. Finally, after
3324 * remaining idle, each queue receives very quickly a new
3325 * request. It follows that the two queues are served
3326 * alternatively, preempting each other if needed. This
3327 * implies that, although both queues have the same weight,
3328 * the queue with large requests receives a service that is
3329 * 1024/8 times as high as the service received by the other
3332 * On the other hand, device idling is performed, and thus
3333 * pure sector-domain guarantees are provided, for the
3334 * following queues, which are likely to need stronger
3335 * throughput guarantees: weight-raised queues, and queues
3336 * with a higher weight than other queues. When such queues
3337 * are active, sub-condition (i) is false, which triggers
3340 * According to the above considerations, the next variable is
3341 * true (only) if sub-condition (i) holds. To compute the
3342 * value of this variable, we not only use the return value of
3343 * the function bfq_symmetric_scenario(), but also check
3344 * whether bfqq is being weight-raised, because
3345 * bfq_symmetric_scenario() does not take into account also
3346 * weight-raised queues (see comments on
3347 * bfq_weights_tree_add()).
3349 * As a side note, it is worth considering that the above
3350 * device-idling countermeasures may however fail in the
3351 * following unlucky scenario: if idling is (correctly)
3352 * disabled in a time period during which all symmetry
3353 * sub-conditions hold, and hence the device is allowed to
3354 * enqueue many requests, but at some later point in time some
3355 * sub-condition stops to hold, then it may become impossible
3356 * to let requests be served in the desired order until all
3357 * the requests already queued in the device have been served.
3359 asymmetric_scenario
= bfqq
->wr_coeff
> 1 ||
3360 !bfq_symmetric_scenario(bfqd
);
3363 * Finally, there is a case where maximizing throughput is the
3364 * best choice even if it may cause unfairness toward
3365 * bfqq. Such a case is when bfqq became active in a burst of
3366 * queue activations. Queues that became active during a large
3367 * burst benefit only from throughput, as discussed in the
3368 * comments on bfq_handle_burst. Thus, if bfqq became active
3369 * in a burst and not idling the device maximizes throughput,
3370 * then the device must no be idled, because not idling the
3371 * device provides bfqq and all other queues in the burst with
3372 * maximum benefit. Combining this and the above case, we can
3373 * now establish when idling is actually needed to preserve
3374 * service guarantees.
3376 idling_needed_for_service_guarantees
=
3377 asymmetric_scenario
&& !bfq_bfqq_in_large_burst(bfqq
);
3380 * We have now all the components we need to compute the
3381 * return value of the function, which is true only if idling
3382 * either boosts the throughput (without issues), or is
3383 * necessary to preserve service guarantees.
3385 return idling_boosts_thr_without_issues
||
3386 idling_needed_for_service_guarantees
;
3390 * If the in-service queue is empty but the function bfq_bfqq_may_idle
3391 * returns true, then:
3392 * 1) the queue must remain in service and cannot be expired, and
3393 * 2) the device must be idled to wait for the possible arrival of a new
3394 * request for the queue.
3395 * See the comments on the function bfq_bfqq_may_idle for the reasons
3396 * why performing device idling is the best choice to boost the throughput
3397 * and preserve service guarantees when bfq_bfqq_may_idle itself
3400 static bool bfq_bfqq_must_idle(struct bfq_queue
*bfqq
)
3402 return RB_EMPTY_ROOT(&bfqq
->sort_list
) && bfq_bfqq_may_idle(bfqq
);
3406 * Select a queue for service. If we have a current queue in service,
3407 * check whether to continue servicing it, or retrieve and set a new one.
3409 static struct bfq_queue
*bfq_select_queue(struct bfq_data
*bfqd
)
3411 struct bfq_queue
*bfqq
;
3412 struct request
*next_rq
;
3413 enum bfqq_expiration reason
= BFQQE_BUDGET_TIMEOUT
;
3415 bfqq
= bfqd
->in_service_queue
;
3419 bfq_log_bfqq(bfqd
, bfqq
, "select_queue: already in-service queue");
3421 if (bfq_may_expire_for_budg_timeout(bfqq
) &&
3422 !bfq_bfqq_wait_request(bfqq
) &&
3423 !bfq_bfqq_must_idle(bfqq
))
3428 * This loop is rarely executed more than once. Even when it
3429 * happens, it is much more convenient to re-execute this loop
3430 * than to return NULL and trigger a new dispatch to get a
3433 next_rq
= bfqq
->next_rq
;
3435 * If bfqq has requests queued and it has enough budget left to
3436 * serve them, keep the queue, otherwise expire it.
3439 if (bfq_serv_to_charge(next_rq
, bfqq
) >
3440 bfq_bfqq_budget_left(bfqq
)) {
3442 * Expire the queue for budget exhaustion,
3443 * which makes sure that the next budget is
3444 * enough to serve the next request, even if
3445 * it comes from the fifo expired path.
3447 reason
= BFQQE_BUDGET_EXHAUSTED
;
3451 * The idle timer may be pending because we may
3452 * not disable disk idling even when a new request
3455 if (bfq_bfqq_wait_request(bfqq
)) {
3457 * If we get here: 1) at least a new request
3458 * has arrived but we have not disabled the
3459 * timer because the request was too small,
3460 * 2) then the block layer has unplugged
3461 * the device, causing the dispatch to be
3464 * Since the device is unplugged, now the
3465 * requests are probably large enough to
3466 * provide a reasonable throughput.
3467 * So we disable idling.
3469 bfq_clear_bfqq_wait_request(bfqq
);
3470 hrtimer_try_to_cancel(&bfqd
->idle_slice_timer
);
3477 * No requests pending. However, if the in-service queue is idling
3478 * for a new request, or has requests waiting for a completion and
3479 * may idle after their completion, then keep it anyway.
3481 if (bfq_bfqq_wait_request(bfqq
) ||
3482 (bfqq
->dispatched
!= 0 && bfq_bfqq_may_idle(bfqq
))) {
3487 reason
= BFQQE_NO_MORE_REQUESTS
;
3489 bfq_bfqq_expire(bfqd
, bfqq
, false, reason
);
3491 bfqq
= bfq_set_in_service_queue(bfqd
);
3493 bfq_log_bfqq(bfqd
, bfqq
, "select_queue: checking new queue");
3498 bfq_log_bfqq(bfqd
, bfqq
, "select_queue: returned this queue");
3500 bfq_log(bfqd
, "select_queue: no queue returned");
3505 static void bfq_update_wr_data(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
3507 struct bfq_entity
*entity
= &bfqq
->entity
;
3509 if (bfqq
->wr_coeff
> 1) { /* queue is being weight-raised */
3510 bfq_log_bfqq(bfqd
, bfqq
,
3511 "raising period dur %u/%u msec, old coeff %u, w %d(%d)",
3512 jiffies_to_msecs(jiffies
- bfqq
->last_wr_start_finish
),
3513 jiffies_to_msecs(bfqq
->wr_cur_max_time
),
3515 bfqq
->entity
.weight
, bfqq
->entity
.orig_weight
);
3517 if (entity
->prio_changed
)
3518 bfq_log_bfqq(bfqd
, bfqq
, "WARN: pending prio change");
3521 * If the queue was activated in a burst, or too much
3522 * time has elapsed from the beginning of this
3523 * weight-raising period, then end weight raising.
3525 if (bfq_bfqq_in_large_burst(bfqq
))
3526 bfq_bfqq_end_wr(bfqq
);
3527 else if (time_is_before_jiffies(bfqq
->last_wr_start_finish
+
3528 bfqq
->wr_cur_max_time
)) {
3529 if (bfqq
->wr_cur_max_time
!= bfqd
->bfq_wr_rt_max_time
||
3530 time_is_before_jiffies(bfqq
->wr_start_at_switch_to_srt
+
3531 bfq_wr_duration(bfqd
)))
3532 bfq_bfqq_end_wr(bfqq
);
3534 switch_back_to_interactive_wr(bfqq
, bfqd
);
3535 bfqq
->entity
.prio_changed
= 1;
3540 * To improve latency (for this or other queues), immediately
3541 * update weight both if it must be raised and if it must be
3542 * lowered. Since, entity may be on some active tree here, and
3543 * might have a pending change of its ioprio class, invoke
3544 * next function with the last parameter unset (see the
3545 * comments on the function).
3547 if ((entity
->weight
> entity
->orig_weight
) != (bfqq
->wr_coeff
> 1))
3548 __bfq_entity_update_weight_prio(bfq_entity_service_tree(entity
),
3553 * Dispatch next request from bfqq.
3555 static struct request
*bfq_dispatch_rq_from_bfqq(struct bfq_data
*bfqd
,
3556 struct bfq_queue
*bfqq
)
3558 struct request
*rq
= bfqq
->next_rq
;
3559 unsigned long service_to_charge
;
3561 service_to_charge
= bfq_serv_to_charge(rq
, bfqq
);
3563 bfq_bfqq_served(bfqq
, service_to_charge
);
3565 bfq_dispatch_remove(bfqd
->queue
, rq
);
3568 * If weight raising has to terminate for bfqq, then next
3569 * function causes an immediate update of bfqq's weight,
3570 * without waiting for next activation. As a consequence, on
3571 * expiration, bfqq will be timestamped as if has never been
3572 * weight-raised during this service slot, even if it has
3573 * received part or even most of the service as a
3574 * weight-raised queue. This inflates bfqq's timestamps, which
3575 * is beneficial, as bfqq is then more willing to leave the
3576 * device immediately to possible other weight-raised queues.
3578 bfq_update_wr_data(bfqd
, bfqq
);
3581 * Expire bfqq, pretending that its budget expired, if bfqq
3582 * belongs to CLASS_IDLE and other queues are waiting for
3585 if (bfqd
->busy_queues
> 1 && bfq_class_idle(bfqq
))
3591 bfq_bfqq_expire(bfqd
, bfqq
, false, BFQQE_BUDGET_EXHAUSTED
);
3595 static bool bfq_has_work(struct blk_mq_hw_ctx
*hctx
)
3597 struct bfq_data
*bfqd
= hctx
->queue
->elevator
->elevator_data
;
3600 * Avoiding lock: a race on bfqd->busy_queues should cause at
3601 * most a call to dispatch for nothing
3603 return !list_empty_careful(&bfqd
->dispatch
) ||
3604 bfqd
->busy_queues
> 0;
3607 static struct request
*__bfq_dispatch_request(struct blk_mq_hw_ctx
*hctx
)
3609 struct bfq_data
*bfqd
= hctx
->queue
->elevator
->elevator_data
;
3610 struct request
*rq
= NULL
;
3611 struct bfq_queue
*bfqq
= NULL
;
3613 if (!list_empty(&bfqd
->dispatch
)) {
3614 rq
= list_first_entry(&bfqd
->dispatch
, struct request
,
3616 list_del_init(&rq
->queuelist
);
3622 * Increment counters here, because this
3623 * dispatch does not follow the standard
3624 * dispatch flow (where counters are
3629 goto inc_in_driver_start_rq
;
3633 * We exploit the put_rq_private hook to decrement
3634 * rq_in_driver, but put_rq_private will not be
3635 * invoked on this request. So, to avoid unbalance,
3636 * just start this request, without incrementing
3637 * rq_in_driver. As a negative consequence,
3638 * rq_in_driver is deceptively lower than it should be
3639 * while this request is in service. This may cause
3640 * bfq_schedule_dispatch to be invoked uselessly.
3642 * As for implementing an exact solution, the
3643 * put_request hook, if defined, is probably invoked
3644 * also on this request. So, by exploiting this hook,
3645 * we could 1) increment rq_in_driver here, and 2)
3646 * decrement it in put_request. Such a solution would
3647 * let the value of the counter be always accurate,
3648 * but it would entail using an extra interface
3649 * function. This cost seems higher than the benefit,
3650 * being the frequency of non-elevator-private
3651 * requests very low.
3656 bfq_log(bfqd
, "dispatch requests: %d busy queues", bfqd
->busy_queues
);
3658 if (bfqd
->busy_queues
== 0)
3662 * Force device to serve one request at a time if
3663 * strict_guarantees is true. Forcing this service scheme is
3664 * currently the ONLY way to guarantee that the request
3665 * service order enforced by the scheduler is respected by a
3666 * queueing device. Otherwise the device is free even to make
3667 * some unlucky request wait for as long as the device
3670 * Of course, serving one request at at time may cause loss of
3673 if (bfqd
->strict_guarantees
&& bfqd
->rq_in_driver
> 0)
3676 bfqq
= bfq_select_queue(bfqd
);
3680 rq
= bfq_dispatch_rq_from_bfqq(bfqd
, bfqq
);
3683 inc_in_driver_start_rq
:
3684 bfqd
->rq_in_driver
++;
3686 rq
->rq_flags
|= RQF_STARTED
;
3692 static struct request
*bfq_dispatch_request(struct blk_mq_hw_ctx
*hctx
)
3694 struct bfq_data
*bfqd
= hctx
->queue
->elevator
->elevator_data
;
3696 #if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
3697 struct bfq_queue
*in_serv_queue
, *bfqq
;
3698 bool waiting_rq
, idle_timer_disabled
;
3701 spin_lock_irq(&bfqd
->lock
);
3703 #if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
3704 in_serv_queue
= bfqd
->in_service_queue
;
3705 waiting_rq
= in_serv_queue
&& bfq_bfqq_wait_request(in_serv_queue
);
3707 rq
= __bfq_dispatch_request(hctx
);
3709 idle_timer_disabled
=
3710 waiting_rq
&& !bfq_bfqq_wait_request(in_serv_queue
);
3713 rq
= __bfq_dispatch_request(hctx
);
3715 spin_unlock_irq(&bfqd
->lock
);
3717 #if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
3718 bfqq
= rq
? RQ_BFQQ(rq
) : NULL
;
3719 if (!idle_timer_disabled
&& !bfqq
)
3723 * rq and bfqq are guaranteed to exist until this function
3724 * ends, for the following reasons. First, rq can be
3725 * dispatched to the device, and then can be completed and
3726 * freed, only after this function ends. Second, rq cannot be
3727 * merged (and thus freed because of a merge) any longer,
3728 * because it has already started. Thus rq cannot be freed
3729 * before this function ends, and, since rq has a reference to
3730 * bfqq, the same guarantee holds for bfqq too.
3732 * In addition, the following queue lock guarantees that
3733 * bfqq_group(bfqq) exists as well.
3735 spin_lock_irq(hctx
->queue
->queue_lock
);
3736 if (idle_timer_disabled
)
3738 * Since the idle timer has been disabled,
3739 * in_serv_queue contained some request when
3740 * __bfq_dispatch_request was invoked above, which
3741 * implies that rq was picked exactly from
3742 * in_serv_queue. Thus in_serv_queue == bfqq, and is
3743 * therefore guaranteed to exist because of the above
3746 bfqg_stats_update_idle_time(bfqq_group(in_serv_queue
));
3748 struct bfq_group
*bfqg
= bfqq_group(bfqq
);
3750 bfqg_stats_update_avg_queue_size(bfqg
);
3751 bfqg_stats_set_start_empty_time(bfqg
);
3752 bfqg_stats_update_io_remove(bfqg
, rq
->cmd_flags
);
3754 spin_unlock_irq(hctx
->queue
->queue_lock
);
3761 * Task holds one reference to the queue, dropped when task exits. Each rq
3762 * in-flight on this queue also holds a reference, dropped when rq is freed.
3764 * Scheduler lock must be held here. Recall not to use bfqq after calling
3765 * this function on it.
3767 void bfq_put_queue(struct bfq_queue
*bfqq
)
3769 #ifdef CONFIG_BFQ_GROUP_IOSCHED
3770 struct bfq_group
*bfqg
= bfqq_group(bfqq
);
3774 bfq_log_bfqq(bfqq
->bfqd
, bfqq
, "put_queue: %p %d",
3781 if (!hlist_unhashed(&bfqq
->burst_list_node
)) {
3782 hlist_del_init(&bfqq
->burst_list_node
);
3784 * Decrement also burst size after the removal, if the
3785 * process associated with bfqq is exiting, and thus
3786 * does not contribute to the burst any longer. This
3787 * decrement helps filter out false positives of large
3788 * bursts, when some short-lived process (often due to
3789 * the execution of commands by some service) happens
3790 * to start and exit while a complex application is
3791 * starting, and thus spawning several processes that
3792 * do I/O (and that *must not* be treated as a large
3793 * burst, see comments on bfq_handle_burst).
3795 * In particular, the decrement is performed only if:
3796 * 1) bfqq is not a merged queue, because, if it is,
3797 * then this free of bfqq is not triggered by the exit
3798 * of the process bfqq is associated with, but exactly
3799 * by the fact that bfqq has just been merged.
3800 * 2) burst_size is greater than 0, to handle
3801 * unbalanced decrements. Unbalanced decrements may
3802 * happen in te following case: bfqq is inserted into
3803 * the current burst list--without incrementing
3804 * bust_size--because of a split, but the current
3805 * burst list is not the burst list bfqq belonged to
3806 * (see comments on the case of a split in
3809 if (bfqq
->bic
&& bfqq
->bfqd
->burst_size
> 0)
3810 bfqq
->bfqd
->burst_size
--;
3813 kmem_cache_free(bfq_pool
, bfqq
);
3814 #ifdef CONFIG_BFQ_GROUP_IOSCHED
3815 bfqg_and_blkg_put(bfqg
);
3819 static void bfq_put_cooperator(struct bfq_queue
*bfqq
)
3821 struct bfq_queue
*__bfqq
, *next
;
3824 * If this queue was scheduled to merge with another queue, be
3825 * sure to drop the reference taken on that queue (and others in
3826 * the merge chain). See bfq_setup_merge and bfq_merge_bfqqs.
3828 __bfqq
= bfqq
->new_bfqq
;
3832 next
= __bfqq
->new_bfqq
;
3833 bfq_put_queue(__bfqq
);
3838 static void bfq_exit_bfqq(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
3840 if (bfqq
== bfqd
->in_service_queue
) {
3841 __bfq_bfqq_expire(bfqd
, bfqq
);
3842 bfq_schedule_dispatch(bfqd
);
3845 bfq_log_bfqq(bfqd
, bfqq
, "exit_bfqq: %p, %d", bfqq
, bfqq
->ref
);
3847 bfq_put_cooperator(bfqq
);
3849 bfq_put_queue(bfqq
); /* release process reference */
3852 static void bfq_exit_icq_bfqq(struct bfq_io_cq
*bic
, bool is_sync
)
3854 struct bfq_queue
*bfqq
= bic_to_bfqq(bic
, is_sync
);
3855 struct bfq_data
*bfqd
;
3858 bfqd
= bfqq
->bfqd
; /* NULL if scheduler already exited */
3861 unsigned long flags
;
3863 spin_lock_irqsave(&bfqd
->lock
, flags
);
3864 bfq_exit_bfqq(bfqd
, bfqq
);
3865 bic_set_bfqq(bic
, NULL
, is_sync
);
3866 spin_unlock_irqrestore(&bfqd
->lock
, flags
);
3870 static void bfq_exit_icq(struct io_cq
*icq
)
3872 struct bfq_io_cq
*bic
= icq_to_bic(icq
);
3874 bfq_exit_icq_bfqq(bic
, true);
3875 bfq_exit_icq_bfqq(bic
, false);
3879 * Update the entity prio values; note that the new values will not
3880 * be used until the next (re)activation.
3883 bfq_set_next_ioprio_data(struct bfq_queue
*bfqq
, struct bfq_io_cq
*bic
)
3885 struct task_struct
*tsk
= current
;
3887 struct bfq_data
*bfqd
= bfqq
->bfqd
;
3892 ioprio_class
= IOPRIO_PRIO_CLASS(bic
->ioprio
);
3893 switch (ioprio_class
) {
3895 dev_err(bfqq
->bfqd
->queue
->backing_dev_info
->dev
,
3896 "bfq: bad prio class %d\n", ioprio_class
);
3898 case IOPRIO_CLASS_NONE
:
3900 * No prio set, inherit CPU scheduling settings.
3902 bfqq
->new_ioprio
= task_nice_ioprio(tsk
);
3903 bfqq
->new_ioprio_class
= task_nice_ioclass(tsk
);
3905 case IOPRIO_CLASS_RT
:
3906 bfqq
->new_ioprio
= IOPRIO_PRIO_DATA(bic
->ioprio
);
3907 bfqq
->new_ioprio_class
= IOPRIO_CLASS_RT
;
3909 case IOPRIO_CLASS_BE
:
3910 bfqq
->new_ioprio
= IOPRIO_PRIO_DATA(bic
->ioprio
);
3911 bfqq
->new_ioprio_class
= IOPRIO_CLASS_BE
;
3913 case IOPRIO_CLASS_IDLE
:
3914 bfqq
->new_ioprio_class
= IOPRIO_CLASS_IDLE
;
3915 bfqq
->new_ioprio
= 7;
3919 if (bfqq
->new_ioprio
>= IOPRIO_BE_NR
) {
3920 pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n",
3922 bfqq
->new_ioprio
= IOPRIO_BE_NR
;
3925 bfqq
->entity
.new_weight
= bfq_ioprio_to_weight(bfqq
->new_ioprio
);
3926 bfqq
->entity
.prio_changed
= 1;
3929 static struct bfq_queue
*bfq_get_queue(struct bfq_data
*bfqd
,
3930 struct bio
*bio
, bool is_sync
,
3931 struct bfq_io_cq
*bic
);
3933 static void bfq_check_ioprio_change(struct bfq_io_cq
*bic
, struct bio
*bio
)
3935 struct bfq_data
*bfqd
= bic_to_bfqd(bic
);
3936 struct bfq_queue
*bfqq
;
3937 int ioprio
= bic
->icq
.ioc
->ioprio
;
3940 * This condition may trigger on a newly created bic, be sure to
3941 * drop the lock before returning.
3943 if (unlikely(!bfqd
) || likely(bic
->ioprio
== ioprio
))
3946 bic
->ioprio
= ioprio
;
3948 bfqq
= bic_to_bfqq(bic
, false);
3950 /* release process reference on this queue */
3951 bfq_put_queue(bfqq
);
3952 bfqq
= bfq_get_queue(bfqd
, bio
, BLK_RW_ASYNC
, bic
);
3953 bic_set_bfqq(bic
, bfqq
, false);
3956 bfqq
= bic_to_bfqq(bic
, true);
3958 bfq_set_next_ioprio_data(bfqq
, bic
);
3961 static void bfq_init_bfqq(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
,
3962 struct bfq_io_cq
*bic
, pid_t pid
, int is_sync
)
3964 RB_CLEAR_NODE(&bfqq
->entity
.rb_node
);
3965 INIT_LIST_HEAD(&bfqq
->fifo
);
3966 INIT_HLIST_NODE(&bfqq
->burst_list_node
);
3972 bfq_set_next_ioprio_data(bfqq
, bic
);
3976 * No need to mark as has_short_ttime if in
3977 * idle_class, because no device idling is performed
3978 * for queues in idle class
3980 if (!bfq_class_idle(bfqq
))
3981 /* tentatively mark as has_short_ttime */
3982 bfq_mark_bfqq_has_short_ttime(bfqq
);
3983 bfq_mark_bfqq_sync(bfqq
);
3984 bfq_mark_bfqq_just_created(bfqq
);
3986 bfq_clear_bfqq_sync(bfqq
);
3988 /* set end request to minus infinity from now */
3989 bfqq
->ttime
.last_end_request
= ktime_get_ns() + 1;
3991 bfq_mark_bfqq_IO_bound(bfqq
);
3995 /* Tentative initial value to trade off between thr and lat */
3996 bfqq
->max_budget
= (2 * bfq_max_budget(bfqd
)) / 3;
3997 bfqq
->budget_timeout
= bfq_smallest_from_now();
4000 bfqq
->last_wr_start_finish
= jiffies
;
4001 bfqq
->wr_start_at_switch_to_srt
= bfq_smallest_from_now();
4002 bfqq
->split_time
= bfq_smallest_from_now();
4005 * Set to the value for which bfqq will not be deemed as
4006 * soft rt when it becomes backlogged.
4008 bfqq
->soft_rt_next_start
= bfq_greatest_from_now();
4010 /* first request is almost certainly seeky */
4011 bfqq
->seek_history
= 1;
4014 static struct bfq_queue
**bfq_async_queue_prio(struct bfq_data
*bfqd
,
4015 struct bfq_group
*bfqg
,
4016 int ioprio_class
, int ioprio
)
4018 switch (ioprio_class
) {
4019 case IOPRIO_CLASS_RT
:
4020 return &bfqg
->async_bfqq
[0][ioprio
];
4021 case IOPRIO_CLASS_NONE
:
4022 ioprio
= IOPRIO_NORM
;
4024 case IOPRIO_CLASS_BE
:
4025 return &bfqg
->async_bfqq
[1][ioprio
];
4026 case IOPRIO_CLASS_IDLE
:
4027 return &bfqg
->async_idle_bfqq
;
4033 static struct bfq_queue
*bfq_get_queue(struct bfq_data
*bfqd
,
4034 struct bio
*bio
, bool is_sync
,
4035 struct bfq_io_cq
*bic
)
4037 const int ioprio
= IOPRIO_PRIO_DATA(bic
->ioprio
);
4038 const int ioprio_class
= IOPRIO_PRIO_CLASS(bic
->ioprio
);
4039 struct bfq_queue
**async_bfqq
= NULL
;
4040 struct bfq_queue
*bfqq
;
4041 struct bfq_group
*bfqg
;
4045 bfqg
= bfq_find_set_group(bfqd
, bio_blkcg(bio
));
4047 bfqq
= &bfqd
->oom_bfqq
;
4052 async_bfqq
= bfq_async_queue_prio(bfqd
, bfqg
, ioprio_class
,
4059 bfqq
= kmem_cache_alloc_node(bfq_pool
,
4060 GFP_NOWAIT
| __GFP_ZERO
| __GFP_NOWARN
,
4064 bfq_init_bfqq(bfqd
, bfqq
, bic
, current
->pid
,
4066 bfq_init_entity(&bfqq
->entity
, bfqg
);
4067 bfq_log_bfqq(bfqd
, bfqq
, "allocated");
4069 bfqq
= &bfqd
->oom_bfqq
;
4070 bfq_log_bfqq(bfqd
, bfqq
, "using oom bfqq");
4075 * Pin the queue now that it's allocated, scheduler exit will
4080 * Extra group reference, w.r.t. sync
4081 * queue. This extra reference is removed
4082 * only if bfqq->bfqg disappears, to
4083 * guarantee that this queue is not freed
4084 * until its group goes away.
4086 bfq_log_bfqq(bfqd
, bfqq
, "get_queue, bfqq not in async: %p, %d",
4092 bfqq
->ref
++; /* get a process reference to this queue */
4093 bfq_log_bfqq(bfqd
, bfqq
, "get_queue, at end: %p, %d", bfqq
, bfqq
->ref
);
4098 static void bfq_update_io_thinktime(struct bfq_data
*bfqd
,
4099 struct bfq_queue
*bfqq
)
4101 struct bfq_ttime
*ttime
= &bfqq
->ttime
;
4102 u64 elapsed
= ktime_get_ns() - bfqq
->ttime
.last_end_request
;
4104 elapsed
= min_t(u64
, elapsed
, 2ULL * bfqd
->bfq_slice_idle
);
4106 ttime
->ttime_samples
= (7*bfqq
->ttime
.ttime_samples
+ 256) / 8;
4107 ttime
->ttime_total
= div_u64(7*ttime
->ttime_total
+ 256*elapsed
, 8);
4108 ttime
->ttime_mean
= div64_ul(ttime
->ttime_total
+ 128,
4109 ttime
->ttime_samples
);
4113 bfq_update_io_seektime(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
,
4116 bfqq
->seek_history
<<= 1;
4117 bfqq
->seek_history
|=
4118 get_sdist(bfqq
->last_request_pos
, rq
) > BFQQ_SEEK_THR
&&
4119 (!blk_queue_nonrot(bfqd
->queue
) ||
4120 blk_rq_sectors(rq
) < BFQQ_SECT_THR_NONROT
);
4123 static void bfq_update_has_short_ttime(struct bfq_data
*bfqd
,
4124 struct bfq_queue
*bfqq
,
4125 struct bfq_io_cq
*bic
)
4127 bool has_short_ttime
= true;
4130 * No need to update has_short_ttime if bfqq is async or in
4131 * idle io prio class, or if bfq_slice_idle is zero, because
4132 * no device idling is performed for bfqq in this case.
4134 if (!bfq_bfqq_sync(bfqq
) || bfq_class_idle(bfqq
) ||
4135 bfqd
->bfq_slice_idle
== 0)
4138 /* Idle window just restored, statistics are meaningless. */
4139 if (time_is_after_eq_jiffies(bfqq
->split_time
+
4140 bfqd
->bfq_wr_min_idle_time
))
4143 /* Think time is infinite if no process is linked to
4144 * bfqq. Otherwise check average think time to
4145 * decide whether to mark as has_short_ttime
4147 if (atomic_read(&bic
->icq
.ioc
->active_ref
) == 0 ||
4148 (bfq_sample_valid(bfqq
->ttime
.ttime_samples
) &&
4149 bfqq
->ttime
.ttime_mean
> bfqd
->bfq_slice_idle
))
4150 has_short_ttime
= false;
4152 bfq_log_bfqq(bfqd
, bfqq
, "update_has_short_ttime: has_short_ttime %d",
4155 if (has_short_ttime
)
4156 bfq_mark_bfqq_has_short_ttime(bfqq
);
4158 bfq_clear_bfqq_has_short_ttime(bfqq
);
4162 * Called when a new fs request (rq) is added to bfqq. Check if there's
4163 * something we should do about it.
4165 static void bfq_rq_enqueued(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
,
4168 struct bfq_io_cq
*bic
= RQ_BIC(rq
);
4170 if (rq
->cmd_flags
& REQ_META
)
4171 bfqq
->meta_pending
++;
4173 bfq_update_io_thinktime(bfqd
, bfqq
);
4174 bfq_update_has_short_ttime(bfqd
, bfqq
, bic
);
4175 bfq_update_io_seektime(bfqd
, bfqq
, rq
);
4177 bfq_log_bfqq(bfqd
, bfqq
,
4178 "rq_enqueued: has_short_ttime=%d (seeky %d)",
4179 bfq_bfqq_has_short_ttime(bfqq
), BFQQ_SEEKY(bfqq
));
4181 bfqq
->last_request_pos
= blk_rq_pos(rq
) + blk_rq_sectors(rq
);
4183 if (bfqq
== bfqd
->in_service_queue
&& bfq_bfqq_wait_request(bfqq
)) {
4184 bool small_req
= bfqq
->queued
[rq_is_sync(rq
)] == 1 &&
4185 blk_rq_sectors(rq
) < 32;
4186 bool budget_timeout
= bfq_bfqq_budget_timeout(bfqq
);
4189 * There is just this request queued: if the request
4190 * is small and the queue is not to be expired, then
4193 * In this way, if the device is being idled to wait
4194 * for a new request from the in-service queue, we
4195 * avoid unplugging the device and committing the
4196 * device to serve just a small request. On the
4197 * contrary, we wait for the block layer to decide
4198 * when to unplug the device: hopefully, new requests
4199 * will be merged to this one quickly, then the device
4200 * will be unplugged and larger requests will be
4203 if (small_req
&& !budget_timeout
)
4207 * A large enough request arrived, or the queue is to
4208 * be expired: in both cases disk idling is to be
4209 * stopped, so clear wait_request flag and reset
4212 bfq_clear_bfqq_wait_request(bfqq
);
4213 hrtimer_try_to_cancel(&bfqd
->idle_slice_timer
);
4216 * The queue is not empty, because a new request just
4217 * arrived. Hence we can safely expire the queue, in
4218 * case of budget timeout, without risking that the
4219 * timestamps of the queue are not updated correctly.
4220 * See [1] for more details.
4223 bfq_bfqq_expire(bfqd
, bfqq
, false,
4224 BFQQE_BUDGET_TIMEOUT
);
4228 /* returns true if it causes the idle timer to be disabled */
4229 static bool __bfq_insert_request(struct bfq_data
*bfqd
, struct request
*rq
)
4231 struct bfq_queue
*bfqq
= RQ_BFQQ(rq
),
4232 *new_bfqq
= bfq_setup_cooperator(bfqd
, bfqq
, rq
, true);
4233 bool waiting
, idle_timer_disabled
= false;
4236 if (bic_to_bfqq(RQ_BIC(rq
), 1) != bfqq
)
4237 new_bfqq
= bic_to_bfqq(RQ_BIC(rq
), 1);
4239 * Release the request's reference to the old bfqq
4240 * and make sure one is taken to the shared queue.
4242 new_bfqq
->allocated
++;
4246 * If the bic associated with the process
4247 * issuing this request still points to bfqq
4248 * (and thus has not been already redirected
4249 * to new_bfqq or even some other bfq_queue),
4250 * then complete the merge and redirect it to
4253 if (bic_to_bfqq(RQ_BIC(rq
), 1) == bfqq
)
4254 bfq_merge_bfqqs(bfqd
, RQ_BIC(rq
),
4257 bfq_clear_bfqq_just_created(bfqq
);
4259 * rq is about to be enqueued into new_bfqq,
4260 * release rq reference on bfqq
4262 bfq_put_queue(bfqq
);
4263 rq
->elv
.priv
[1] = new_bfqq
;
4267 waiting
= bfqq
&& bfq_bfqq_wait_request(bfqq
);
4268 bfq_add_request(rq
);
4269 idle_timer_disabled
= waiting
&& !bfq_bfqq_wait_request(bfqq
);
4271 rq
->fifo_time
= ktime_get_ns() + bfqd
->bfq_fifo_expire
[rq_is_sync(rq
)];
4272 list_add_tail(&rq
->queuelist
, &bfqq
->fifo
);
4274 bfq_rq_enqueued(bfqd
, bfqq
, rq
);
4276 return idle_timer_disabled
;
4279 static void bfq_insert_request(struct blk_mq_hw_ctx
*hctx
, struct request
*rq
,
4282 struct request_queue
*q
= hctx
->queue
;
4283 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
4284 #if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
4285 struct bfq_queue
*bfqq
= RQ_BFQQ(rq
);
4286 bool idle_timer_disabled
= false;
4287 unsigned int cmd_flags
;
4290 spin_lock_irq(&bfqd
->lock
);
4291 if (blk_mq_sched_try_insert_merge(q
, rq
)) {
4292 spin_unlock_irq(&bfqd
->lock
);
4296 spin_unlock_irq(&bfqd
->lock
);
4298 blk_mq_sched_request_inserted(rq
);
4300 spin_lock_irq(&bfqd
->lock
);
4301 if (at_head
|| blk_rq_is_passthrough(rq
)) {
4303 list_add(&rq
->queuelist
, &bfqd
->dispatch
);
4305 list_add_tail(&rq
->queuelist
, &bfqd
->dispatch
);
4307 #if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
4308 idle_timer_disabled
= __bfq_insert_request(bfqd
, rq
);
4310 * Update bfqq, because, if a queue merge has occurred
4311 * in __bfq_insert_request, then rq has been
4312 * redirected into a new queue.
4316 __bfq_insert_request(bfqd
, rq
);
4319 if (rq_mergeable(rq
)) {
4320 elv_rqhash_add(q
, rq
);
4326 #if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
4328 * Cache cmd_flags before releasing scheduler lock, because rq
4329 * may disappear afterwards (for example, because of a request
4332 cmd_flags
= rq
->cmd_flags
;
4334 spin_unlock_irq(&bfqd
->lock
);
4336 #if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
4340 * bfqq still exists, because it can disappear only after
4341 * either it is merged with another queue, or the process it
4342 * is associated with exits. But both actions must be taken by
4343 * the same process currently executing this flow of
4346 * In addition, the following queue lock guarantees that
4347 * bfqq_group(bfqq) exists as well.
4349 spin_lock_irq(q
->queue_lock
);
4350 bfqg_stats_update_io_add(bfqq_group(bfqq
), bfqq
, cmd_flags
);
4351 if (idle_timer_disabled
)
4352 bfqg_stats_update_idle_time(bfqq_group(bfqq
));
4353 spin_unlock_irq(q
->queue_lock
);
4357 static void bfq_insert_requests(struct blk_mq_hw_ctx
*hctx
,
4358 struct list_head
*list
, bool at_head
)
4360 while (!list_empty(list
)) {
4363 rq
= list_first_entry(list
, struct request
, queuelist
);
4364 list_del_init(&rq
->queuelist
);
4365 bfq_insert_request(hctx
, rq
, at_head
);
4369 static void bfq_update_hw_tag(struct bfq_data
*bfqd
)
4371 bfqd
->max_rq_in_driver
= max_t(int, bfqd
->max_rq_in_driver
,
4372 bfqd
->rq_in_driver
);
4374 if (bfqd
->hw_tag
== 1)
4378 * This sample is valid if the number of outstanding requests
4379 * is large enough to allow a queueing behavior. Note that the
4380 * sum is not exact, as it's not taking into account deactivated
4383 if (bfqd
->rq_in_driver
+ bfqd
->queued
< BFQ_HW_QUEUE_THRESHOLD
)
4386 if (bfqd
->hw_tag_samples
++ < BFQ_HW_QUEUE_SAMPLES
)
4389 bfqd
->hw_tag
= bfqd
->max_rq_in_driver
> BFQ_HW_QUEUE_THRESHOLD
;
4390 bfqd
->max_rq_in_driver
= 0;
4391 bfqd
->hw_tag_samples
= 0;
4394 static void bfq_completed_request(struct bfq_queue
*bfqq
, struct bfq_data
*bfqd
)
4399 bfq_update_hw_tag(bfqd
);
4401 bfqd
->rq_in_driver
--;
4404 if (!bfqq
->dispatched
&& !bfq_bfqq_busy(bfqq
)) {
4406 * Set budget_timeout (which we overload to store the
4407 * time at which the queue remains with no backlog and
4408 * no outstanding request; used by the weight-raising
4411 bfqq
->budget_timeout
= jiffies
;
4413 bfq_weights_tree_remove(bfqd
, &bfqq
->entity
,
4414 &bfqd
->queue_weights_tree
);
4417 now_ns
= ktime_get_ns();
4419 bfqq
->ttime
.last_end_request
= now_ns
;
4422 * Using us instead of ns, to get a reasonable precision in
4423 * computing rate in next check.
4425 delta_us
= div_u64(now_ns
- bfqd
->last_completion
, NSEC_PER_USEC
);
4428 * If the request took rather long to complete, and, according
4429 * to the maximum request size recorded, this completion latency
4430 * implies that the request was certainly served at a very low
4431 * rate (less than 1M sectors/sec), then the whole observation
4432 * interval that lasts up to this time instant cannot be a
4433 * valid time interval for computing a new peak rate. Invoke
4434 * bfq_update_rate_reset to have the following three steps
4436 * - close the observation interval at the last (previous)
4437 * request dispatch or completion
4438 * - compute rate, if possible, for that observation interval
4439 * - reset to zero samples, which will trigger a proper
4440 * re-initialization of the observation interval on next
4443 if (delta_us
> BFQ_MIN_TT
/NSEC_PER_USEC
&&
4444 (bfqd
->last_rq_max_size
<<BFQ_RATE_SHIFT
)/delta_us
<
4445 1UL<<(BFQ_RATE_SHIFT
- 10))
4446 bfq_update_rate_reset(bfqd
, NULL
);
4447 bfqd
->last_completion
= now_ns
;
4450 * If we are waiting to discover whether the request pattern
4451 * of the task associated with the queue is actually
4452 * isochronous, and both requisites for this condition to hold
4453 * are now satisfied, then compute soft_rt_next_start (see the
4454 * comments on the function bfq_bfqq_softrt_next_start()). We
4455 * schedule this delayed check when bfqq expires, if it still
4456 * has in-flight requests.
4458 if (bfq_bfqq_softrt_update(bfqq
) && bfqq
->dispatched
== 0 &&
4459 RB_EMPTY_ROOT(&bfqq
->sort_list
))
4460 bfqq
->soft_rt_next_start
=
4461 bfq_bfqq_softrt_next_start(bfqd
, bfqq
);
4464 * If this is the in-service queue, check if it needs to be expired,
4465 * or if we want to idle in case it has no pending requests.
4467 if (bfqd
->in_service_queue
== bfqq
) {
4468 if (bfqq
->dispatched
== 0 && bfq_bfqq_must_idle(bfqq
)) {
4469 bfq_arm_slice_timer(bfqd
);
4471 } else if (bfq_may_expire_for_budg_timeout(bfqq
))
4472 bfq_bfqq_expire(bfqd
, bfqq
, false,
4473 BFQQE_BUDGET_TIMEOUT
);
4474 else if (RB_EMPTY_ROOT(&bfqq
->sort_list
) &&
4475 (bfqq
->dispatched
== 0 ||
4476 !bfq_bfqq_may_idle(bfqq
)))
4477 bfq_bfqq_expire(bfqd
, bfqq
, false,
4478 BFQQE_NO_MORE_REQUESTS
);
4481 if (!bfqd
->rq_in_driver
)
4482 bfq_schedule_dispatch(bfqd
);
4485 static void bfq_put_rq_priv_body(struct bfq_queue
*bfqq
)
4489 bfq_put_queue(bfqq
);
4492 static void bfq_finish_request(struct request
*rq
)
4494 struct bfq_queue
*bfqq
;
4495 struct bfq_data
*bfqd
;
4503 if (rq
->rq_flags
& RQF_STARTED
)
4504 bfqg_stats_update_completion(bfqq_group(bfqq
),
4505 rq_start_time_ns(rq
),
4506 rq_io_start_time_ns(rq
),
4509 if (likely(rq
->rq_flags
& RQF_STARTED
)) {
4510 unsigned long flags
;
4512 spin_lock_irqsave(&bfqd
->lock
, flags
);
4514 bfq_completed_request(bfqq
, bfqd
);
4515 bfq_put_rq_priv_body(bfqq
);
4517 spin_unlock_irqrestore(&bfqd
->lock
, flags
);
4520 * Request rq may be still/already in the scheduler,
4521 * in which case we need to remove it. And we cannot
4522 * defer such a check and removal, to avoid
4523 * inconsistencies in the time interval from the end
4524 * of this function to the start of the deferred work.
4525 * This situation seems to occur only in process
4526 * context, as a consequence of a merge. In the
4527 * current version of the code, this implies that the
4531 if (!RB_EMPTY_NODE(&rq
->rb_node
)) {
4532 bfq_remove_request(rq
->q
, rq
);
4533 bfqg_stats_update_io_remove(bfqq_group(bfqq
),
4536 bfq_put_rq_priv_body(bfqq
);
4539 rq
->elv
.priv
[0] = NULL
;
4540 rq
->elv
.priv
[1] = NULL
;
4544 * Returns NULL if a new bfqq should be allocated, or the old bfqq if this
4545 * was the last process referring to that bfqq.
4547 static struct bfq_queue
*
4548 bfq_split_bfqq(struct bfq_io_cq
*bic
, struct bfq_queue
*bfqq
)
4550 bfq_log_bfqq(bfqq
->bfqd
, bfqq
, "splitting queue");
4552 if (bfqq_process_refs(bfqq
) == 1) {
4553 bfqq
->pid
= current
->pid
;
4554 bfq_clear_bfqq_coop(bfqq
);
4555 bfq_clear_bfqq_split_coop(bfqq
);
4559 bic_set_bfqq(bic
, NULL
, 1);
4561 bfq_put_cooperator(bfqq
);
4563 bfq_put_queue(bfqq
);
4567 static struct bfq_queue
*bfq_get_bfqq_handle_split(struct bfq_data
*bfqd
,
4568 struct bfq_io_cq
*bic
,
4570 bool split
, bool is_sync
,
4573 struct bfq_queue
*bfqq
= bic_to_bfqq(bic
, is_sync
);
4575 if (likely(bfqq
&& bfqq
!= &bfqd
->oom_bfqq
))
4582 bfq_put_queue(bfqq
);
4583 bfqq
= bfq_get_queue(bfqd
, bio
, is_sync
, bic
);
4585 bic_set_bfqq(bic
, bfqq
, is_sync
);
4586 if (split
&& is_sync
) {
4587 if ((bic
->was_in_burst_list
&& bfqd
->large_burst
) ||
4588 bic
->saved_in_large_burst
)
4589 bfq_mark_bfqq_in_large_burst(bfqq
);
4591 bfq_clear_bfqq_in_large_burst(bfqq
);
4592 if (bic
->was_in_burst_list
)
4594 * If bfqq was in the current
4595 * burst list before being
4596 * merged, then we have to add
4597 * it back. And we do not need
4598 * to increase burst_size, as
4599 * we did not decrement
4600 * burst_size when we removed
4601 * bfqq from the burst list as
4602 * a consequence of a merge
4604 * bfq_put_queue). In this
4605 * respect, it would be rather
4606 * costly to know whether the
4607 * current burst list is still
4608 * the same burst list from
4609 * which bfqq was removed on
4610 * the merge. To avoid this
4611 * cost, if bfqq was in a
4612 * burst list, then we add
4613 * bfqq to the current burst
4614 * list without any further
4615 * check. This can cause
4616 * inappropriate insertions,
4617 * but rarely enough to not
4618 * harm the detection of large
4619 * bursts significantly.
4621 hlist_add_head(&bfqq
->burst_list_node
,
4624 bfqq
->split_time
= jiffies
;
4631 * Allocate bfq data structures associated with this request.
4633 static void bfq_prepare_request(struct request
*rq
, struct bio
*bio
)
4635 struct request_queue
*q
= rq
->q
;
4636 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
4637 struct bfq_io_cq
*bic
;
4638 const int is_sync
= rq_is_sync(rq
);
4639 struct bfq_queue
*bfqq
;
4640 bool new_queue
= false;
4641 bool bfqq_already_existing
= false, split
= false;
4645 bic
= icq_to_bic(rq
->elv
.icq
);
4647 spin_lock_irq(&bfqd
->lock
);
4649 bfq_check_ioprio_change(bic
, bio
);
4651 bfq_bic_update_cgroup(bic
, bio
);
4653 bfqq
= bfq_get_bfqq_handle_split(bfqd
, bic
, bio
, false, is_sync
,
4656 if (likely(!new_queue
)) {
4657 /* If the queue was seeky for too long, break it apart. */
4658 if (bfq_bfqq_coop(bfqq
) && bfq_bfqq_split_coop(bfqq
)) {
4659 bfq_log_bfqq(bfqd
, bfqq
, "breaking apart bfqq");
4661 /* Update bic before losing reference to bfqq */
4662 if (bfq_bfqq_in_large_burst(bfqq
))
4663 bic
->saved_in_large_burst
= true;
4665 bfqq
= bfq_split_bfqq(bic
, bfqq
);
4669 bfqq
= bfq_get_bfqq_handle_split(bfqd
, bic
, bio
,
4673 bfqq_already_existing
= true;
4679 bfq_log_bfqq(bfqd
, bfqq
, "get_request %p: bfqq %p, %d",
4680 rq
, bfqq
, bfqq
->ref
);
4682 rq
->elv
.priv
[0] = bic
;
4683 rq
->elv
.priv
[1] = bfqq
;
4686 * If a bfq_queue has only one process reference, it is owned
4687 * by only this bic: we can then set bfqq->bic = bic. in
4688 * addition, if the queue has also just been split, we have to
4691 if (likely(bfqq
!= &bfqd
->oom_bfqq
) && bfqq_process_refs(bfqq
) == 1) {
4695 * The queue has just been split from a shared
4696 * queue: restore the idle window and the
4697 * possible weight raising period.
4699 bfq_bfqq_resume_state(bfqq
, bfqd
, bic
,
4700 bfqq_already_existing
);
4704 if (unlikely(bfq_bfqq_just_created(bfqq
)))
4705 bfq_handle_burst(bfqd
, bfqq
);
4707 spin_unlock_irq(&bfqd
->lock
);
4710 static void bfq_idle_slice_timer_body(struct bfq_queue
*bfqq
)
4712 struct bfq_data
*bfqd
= bfqq
->bfqd
;
4713 enum bfqq_expiration reason
;
4714 unsigned long flags
;
4716 spin_lock_irqsave(&bfqd
->lock
, flags
);
4717 bfq_clear_bfqq_wait_request(bfqq
);
4719 if (bfqq
!= bfqd
->in_service_queue
) {
4720 spin_unlock_irqrestore(&bfqd
->lock
, flags
);
4724 if (bfq_bfqq_budget_timeout(bfqq
))
4726 * Also here the queue can be safely expired
4727 * for budget timeout without wasting
4730 reason
= BFQQE_BUDGET_TIMEOUT
;
4731 else if (bfqq
->queued
[0] == 0 && bfqq
->queued
[1] == 0)
4733 * The queue may not be empty upon timer expiration,
4734 * because we may not disable the timer when the
4735 * first request of the in-service queue arrives
4736 * during disk idling.
4738 reason
= BFQQE_TOO_IDLE
;
4740 goto schedule_dispatch
;
4742 bfq_bfqq_expire(bfqd
, bfqq
, true, reason
);
4745 spin_unlock_irqrestore(&bfqd
->lock
, flags
);
4746 bfq_schedule_dispatch(bfqd
);
4750 * Handler of the expiration of the timer running if the in-service queue
4751 * is idling inside its time slice.
4753 static enum hrtimer_restart
bfq_idle_slice_timer(struct hrtimer
*timer
)
4755 struct bfq_data
*bfqd
= container_of(timer
, struct bfq_data
,
4757 struct bfq_queue
*bfqq
= bfqd
->in_service_queue
;
4760 * Theoretical race here: the in-service queue can be NULL or
4761 * different from the queue that was idling if a new request
4762 * arrives for the current queue and there is a full dispatch
4763 * cycle that changes the in-service queue. This can hardly
4764 * happen, but in the worst case we just expire a queue too
4768 bfq_idle_slice_timer_body(bfqq
);
4770 return HRTIMER_NORESTART
;
4773 static void __bfq_put_async_bfqq(struct bfq_data
*bfqd
,
4774 struct bfq_queue
**bfqq_ptr
)
4776 struct bfq_queue
*bfqq
= *bfqq_ptr
;
4778 bfq_log(bfqd
, "put_async_bfqq: %p", bfqq
);
4780 bfq_bfqq_move(bfqd
, bfqq
, bfqd
->root_group
);
4782 bfq_log_bfqq(bfqd
, bfqq
, "put_async_bfqq: putting %p, %d",
4784 bfq_put_queue(bfqq
);
4790 * Release all the bfqg references to its async queues. If we are
4791 * deallocating the group these queues may still contain requests, so
4792 * we reparent them to the root cgroup (i.e., the only one that will
4793 * exist for sure until all the requests on a device are gone).
4795 void bfq_put_async_queues(struct bfq_data
*bfqd
, struct bfq_group
*bfqg
)
4799 for (i
= 0; i
< 2; i
++)
4800 for (j
= 0; j
< IOPRIO_BE_NR
; j
++)
4801 __bfq_put_async_bfqq(bfqd
, &bfqg
->async_bfqq
[i
][j
]);
4803 __bfq_put_async_bfqq(bfqd
, &bfqg
->async_idle_bfqq
);
4806 static void bfq_exit_queue(struct elevator_queue
*e
)
4808 struct bfq_data
*bfqd
= e
->elevator_data
;
4809 struct bfq_queue
*bfqq
, *n
;
4811 hrtimer_cancel(&bfqd
->idle_slice_timer
);
4813 spin_lock_irq(&bfqd
->lock
);
4814 list_for_each_entry_safe(bfqq
, n
, &bfqd
->idle_list
, bfqq_list
)
4815 bfq_deactivate_bfqq(bfqd
, bfqq
, false, false);
4816 spin_unlock_irq(&bfqd
->lock
);
4818 hrtimer_cancel(&bfqd
->idle_slice_timer
);
4820 #ifdef CONFIG_BFQ_GROUP_IOSCHED
4821 blkcg_deactivate_policy(bfqd
->queue
, &blkcg_policy_bfq
);
4823 spin_lock_irq(&bfqd
->lock
);
4824 bfq_put_async_queues(bfqd
, bfqd
->root_group
);
4825 kfree(bfqd
->root_group
);
4826 spin_unlock_irq(&bfqd
->lock
);
4832 static void bfq_init_root_group(struct bfq_group
*root_group
,
4833 struct bfq_data
*bfqd
)
4837 #ifdef CONFIG_BFQ_GROUP_IOSCHED
4838 root_group
->entity
.parent
= NULL
;
4839 root_group
->my_entity
= NULL
;
4840 root_group
->bfqd
= bfqd
;
4842 root_group
->rq_pos_tree
= RB_ROOT
;
4843 for (i
= 0; i
< BFQ_IOPRIO_CLASSES
; i
++)
4844 root_group
->sched_data
.service_tree
[i
] = BFQ_SERVICE_TREE_INIT
;
4845 root_group
->sched_data
.bfq_class_idle_last_service
= jiffies
;
4848 static int bfq_init_queue(struct request_queue
*q
, struct elevator_type
*e
)
4850 struct bfq_data
*bfqd
;
4851 struct elevator_queue
*eq
;
4853 eq
= elevator_alloc(q
, e
);
4857 bfqd
= kzalloc_node(sizeof(*bfqd
), GFP_KERNEL
, q
->node
);
4859 kobject_put(&eq
->kobj
);
4862 eq
->elevator_data
= bfqd
;
4864 spin_lock_irq(q
->queue_lock
);
4866 spin_unlock_irq(q
->queue_lock
);
4869 * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
4870 * Grab a permanent reference to it, so that the normal code flow
4871 * will not attempt to free it.
4873 bfq_init_bfqq(bfqd
, &bfqd
->oom_bfqq
, NULL
, 1, 0);
4874 bfqd
->oom_bfqq
.ref
++;
4875 bfqd
->oom_bfqq
.new_ioprio
= BFQ_DEFAULT_QUEUE_IOPRIO
;
4876 bfqd
->oom_bfqq
.new_ioprio_class
= IOPRIO_CLASS_BE
;
4877 bfqd
->oom_bfqq
.entity
.new_weight
=
4878 bfq_ioprio_to_weight(bfqd
->oom_bfqq
.new_ioprio
);
4880 /* oom_bfqq does not participate to bursts */
4881 bfq_clear_bfqq_just_created(&bfqd
->oom_bfqq
);
4884 * Trigger weight initialization, according to ioprio, at the
4885 * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
4886 * class won't be changed any more.
4888 bfqd
->oom_bfqq
.entity
.prio_changed
= 1;
4892 INIT_LIST_HEAD(&bfqd
->dispatch
);
4894 hrtimer_init(&bfqd
->idle_slice_timer
, CLOCK_MONOTONIC
,
4896 bfqd
->idle_slice_timer
.function
= bfq_idle_slice_timer
;
4898 bfqd
->queue_weights_tree
= RB_ROOT
;
4899 bfqd
->group_weights_tree
= RB_ROOT
;
4901 INIT_LIST_HEAD(&bfqd
->active_list
);
4902 INIT_LIST_HEAD(&bfqd
->idle_list
);
4903 INIT_HLIST_HEAD(&bfqd
->burst_list
);
4907 bfqd
->bfq_max_budget
= bfq_default_max_budget
;
4909 bfqd
->bfq_fifo_expire
[0] = bfq_fifo_expire
[0];
4910 bfqd
->bfq_fifo_expire
[1] = bfq_fifo_expire
[1];
4911 bfqd
->bfq_back_max
= bfq_back_max
;
4912 bfqd
->bfq_back_penalty
= bfq_back_penalty
;
4913 bfqd
->bfq_slice_idle
= bfq_slice_idle
;
4914 bfqd
->bfq_timeout
= bfq_timeout
;
4916 bfqd
->bfq_requests_within_timer
= 120;
4918 bfqd
->bfq_large_burst_thresh
= 8;
4919 bfqd
->bfq_burst_interval
= msecs_to_jiffies(180);
4921 bfqd
->low_latency
= true;
4924 * Trade-off between responsiveness and fairness.
4926 bfqd
->bfq_wr_coeff
= 30;
4927 bfqd
->bfq_wr_rt_max_time
= msecs_to_jiffies(300);
4928 bfqd
->bfq_wr_max_time
= 0;
4929 bfqd
->bfq_wr_min_idle_time
= msecs_to_jiffies(2000);
4930 bfqd
->bfq_wr_min_inter_arr_async
= msecs_to_jiffies(500);
4931 bfqd
->bfq_wr_max_softrt_rate
= 7000; /*
4932 * Approximate rate required
4933 * to playback or record a
4934 * high-definition compressed
4937 bfqd
->wr_busy_queues
= 0;
4940 * Begin by assuming, optimistically, that the device is a
4941 * high-speed one, and that its peak rate is equal to 2/3 of
4942 * the highest reference rate.
4944 bfqd
->RT_prod
= R_fast
[blk_queue_nonrot(bfqd
->queue
)] *
4945 T_fast
[blk_queue_nonrot(bfqd
->queue
)];
4946 bfqd
->peak_rate
= R_fast
[blk_queue_nonrot(bfqd
->queue
)] * 2 / 3;
4947 bfqd
->device_speed
= BFQ_BFQD_FAST
;
4949 spin_lock_init(&bfqd
->lock
);
4952 * The invocation of the next bfq_create_group_hierarchy
4953 * function is the head of a chain of function calls
4954 * (bfq_create_group_hierarchy->blkcg_activate_policy->
4955 * blk_mq_freeze_queue) that may lead to the invocation of the
4956 * has_work hook function. For this reason,
4957 * bfq_create_group_hierarchy is invoked only after all
4958 * scheduler data has been initialized, apart from the fields
4959 * that can be initialized only after invoking
4960 * bfq_create_group_hierarchy. This, in particular, enables
4961 * has_work to correctly return false. Of course, to avoid
4962 * other inconsistencies, the blk-mq stack must then refrain
4963 * from invoking further scheduler hooks before this init
4964 * function is finished.
4966 bfqd
->root_group
= bfq_create_group_hierarchy(bfqd
, q
->node
);
4967 if (!bfqd
->root_group
)
4969 bfq_init_root_group(bfqd
->root_group
, bfqd
);
4970 bfq_init_entity(&bfqd
->oom_bfqq
.entity
, bfqd
->root_group
);
4972 wbt_disable_default(q
);
4977 kobject_put(&eq
->kobj
);
4981 static void bfq_slab_kill(void)
4983 kmem_cache_destroy(bfq_pool
);
4986 static int __init
bfq_slab_setup(void)
4988 bfq_pool
= KMEM_CACHE(bfq_queue
, 0);
4994 static ssize_t
bfq_var_show(unsigned int var
, char *page
)
4996 return sprintf(page
, "%u\n", var
);
4999 static int bfq_var_store(unsigned long *var
, const char *page
)
5001 unsigned long new_val
;
5002 int ret
= kstrtoul(page
, 10, &new_val
);
5010 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
5011 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
5013 struct bfq_data *bfqd = e->elevator_data; \
5014 u64 __data = __VAR; \
5016 __data = jiffies_to_msecs(__data); \
5017 else if (__CONV == 2) \
5018 __data = div_u64(__data, NSEC_PER_MSEC); \
5019 return bfq_var_show(__data, (page)); \
5021 SHOW_FUNCTION(bfq_fifo_expire_sync_show
, bfqd
->bfq_fifo_expire
[1], 2);
5022 SHOW_FUNCTION(bfq_fifo_expire_async_show
, bfqd
->bfq_fifo_expire
[0], 2);
5023 SHOW_FUNCTION(bfq_back_seek_max_show
, bfqd
->bfq_back_max
, 0);
5024 SHOW_FUNCTION(bfq_back_seek_penalty_show
, bfqd
->bfq_back_penalty
, 0);
5025 SHOW_FUNCTION(bfq_slice_idle_show
, bfqd
->bfq_slice_idle
, 2);
5026 SHOW_FUNCTION(bfq_max_budget_show
, bfqd
->bfq_user_max_budget
, 0);
5027 SHOW_FUNCTION(bfq_timeout_sync_show
, bfqd
->bfq_timeout
, 1);
5028 SHOW_FUNCTION(bfq_strict_guarantees_show
, bfqd
->strict_guarantees
, 0);
5029 SHOW_FUNCTION(bfq_low_latency_show
, bfqd
->low_latency
, 0);
5030 #undef SHOW_FUNCTION
5032 #define USEC_SHOW_FUNCTION(__FUNC, __VAR) \
5033 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
5035 struct bfq_data *bfqd = e->elevator_data; \
5036 u64 __data = __VAR; \
5037 __data = div_u64(__data, NSEC_PER_USEC); \
5038 return bfq_var_show(__data, (page)); \
5040 USEC_SHOW_FUNCTION(bfq_slice_idle_us_show
, bfqd
->bfq_slice_idle
);
5041 #undef USEC_SHOW_FUNCTION
5043 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
5045 __FUNC(struct elevator_queue *e, const char *page, size_t count) \
5047 struct bfq_data *bfqd = e->elevator_data; \
5048 unsigned long __data, __min = (MIN), __max = (MAX); \
5051 ret = bfq_var_store(&__data, (page)); \
5054 if (__data < __min) \
5056 else if (__data > __max) \
5059 *(__PTR) = msecs_to_jiffies(__data); \
5060 else if (__CONV == 2) \
5061 *(__PTR) = (u64)__data * NSEC_PER_MSEC; \
5063 *(__PTR) = __data; \
5066 STORE_FUNCTION(bfq_fifo_expire_sync_store
, &bfqd
->bfq_fifo_expire
[1], 1,
5068 STORE_FUNCTION(bfq_fifo_expire_async_store
, &bfqd
->bfq_fifo_expire
[0], 1,
5070 STORE_FUNCTION(bfq_back_seek_max_store
, &bfqd
->bfq_back_max
, 0, INT_MAX
, 0);
5071 STORE_FUNCTION(bfq_back_seek_penalty_store
, &bfqd
->bfq_back_penalty
, 1,
5073 STORE_FUNCTION(bfq_slice_idle_store
, &bfqd
->bfq_slice_idle
, 0, INT_MAX
, 2);
5074 #undef STORE_FUNCTION
5076 #define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \
5077 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\
5079 struct bfq_data *bfqd = e->elevator_data; \
5080 unsigned long __data, __min = (MIN), __max = (MAX); \
5083 ret = bfq_var_store(&__data, (page)); \
5086 if (__data < __min) \
5088 else if (__data > __max) \
5090 *(__PTR) = (u64)__data * NSEC_PER_USEC; \
5093 USEC_STORE_FUNCTION(bfq_slice_idle_us_store
, &bfqd
->bfq_slice_idle
, 0,
5095 #undef USEC_STORE_FUNCTION
5097 static ssize_t
bfq_max_budget_store(struct elevator_queue
*e
,
5098 const char *page
, size_t count
)
5100 struct bfq_data
*bfqd
= e
->elevator_data
;
5101 unsigned long __data
;
5104 ret
= bfq_var_store(&__data
, (page
));
5109 bfqd
->bfq_max_budget
= bfq_calc_max_budget(bfqd
);
5111 if (__data
> INT_MAX
)
5113 bfqd
->bfq_max_budget
= __data
;
5116 bfqd
->bfq_user_max_budget
= __data
;
5122 * Leaving this name to preserve name compatibility with cfq
5123 * parameters, but this timeout is used for both sync and async.
5125 static ssize_t
bfq_timeout_sync_store(struct elevator_queue
*e
,
5126 const char *page
, size_t count
)
5128 struct bfq_data
*bfqd
= e
->elevator_data
;
5129 unsigned long __data
;
5132 ret
= bfq_var_store(&__data
, (page
));
5138 else if (__data
> INT_MAX
)
5141 bfqd
->bfq_timeout
= msecs_to_jiffies(__data
);
5142 if (bfqd
->bfq_user_max_budget
== 0)
5143 bfqd
->bfq_max_budget
= bfq_calc_max_budget(bfqd
);
5148 static ssize_t
bfq_strict_guarantees_store(struct elevator_queue
*e
,
5149 const char *page
, size_t count
)
5151 struct bfq_data
*bfqd
= e
->elevator_data
;
5152 unsigned long __data
;
5155 ret
= bfq_var_store(&__data
, (page
));
5161 if (!bfqd
->strict_guarantees
&& __data
== 1
5162 && bfqd
->bfq_slice_idle
< 8 * NSEC_PER_MSEC
)
5163 bfqd
->bfq_slice_idle
= 8 * NSEC_PER_MSEC
;
5165 bfqd
->strict_guarantees
= __data
;
5170 static ssize_t
bfq_low_latency_store(struct elevator_queue
*e
,
5171 const char *page
, size_t count
)
5173 struct bfq_data
*bfqd
= e
->elevator_data
;
5174 unsigned long __data
;
5177 ret
= bfq_var_store(&__data
, (page
));
5183 if (__data
== 0 && bfqd
->low_latency
!= 0)
5185 bfqd
->low_latency
= __data
;
5190 #define BFQ_ATTR(name) \
5191 __ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store)
5193 static struct elv_fs_entry bfq_attrs
[] = {
5194 BFQ_ATTR(fifo_expire_sync
),
5195 BFQ_ATTR(fifo_expire_async
),
5196 BFQ_ATTR(back_seek_max
),
5197 BFQ_ATTR(back_seek_penalty
),
5198 BFQ_ATTR(slice_idle
),
5199 BFQ_ATTR(slice_idle_us
),
5200 BFQ_ATTR(max_budget
),
5201 BFQ_ATTR(timeout_sync
),
5202 BFQ_ATTR(strict_guarantees
),
5203 BFQ_ATTR(low_latency
),
5207 static struct elevator_type iosched_bfq_mq
= {
5209 .prepare_request
= bfq_prepare_request
,
5210 .finish_request
= bfq_finish_request
,
5211 .exit_icq
= bfq_exit_icq
,
5212 .insert_requests
= bfq_insert_requests
,
5213 .dispatch_request
= bfq_dispatch_request
,
5214 .next_request
= elv_rb_latter_request
,
5215 .former_request
= elv_rb_former_request
,
5216 .allow_merge
= bfq_allow_bio_merge
,
5217 .bio_merge
= bfq_bio_merge
,
5218 .request_merge
= bfq_request_merge
,
5219 .requests_merged
= bfq_requests_merged
,
5220 .request_merged
= bfq_request_merged
,
5221 .has_work
= bfq_has_work
,
5222 .init_sched
= bfq_init_queue
,
5223 .exit_sched
= bfq_exit_queue
,
5227 .icq_size
= sizeof(struct bfq_io_cq
),
5228 .icq_align
= __alignof__(struct bfq_io_cq
),
5229 .elevator_attrs
= bfq_attrs
,
5230 .elevator_name
= "bfq",
5231 .elevator_owner
= THIS_MODULE
,
5233 MODULE_ALIAS("bfq-iosched");
5235 static int __init
bfq_init(void)
5239 #ifdef CONFIG_BFQ_GROUP_IOSCHED
5240 ret
= blkcg_policy_register(&blkcg_policy_bfq
);
5246 if (bfq_slab_setup())
5250 * Times to load large popular applications for the typical
5251 * systems installed on the reference devices (see the
5252 * comments before the definitions of the next two
5253 * arrays). Actually, we use slightly slower values, as the
5254 * estimated peak rate tends to be smaller than the actual
5255 * peak rate. The reason for this last fact is that estimates
5256 * are computed over much shorter time intervals than the long
5257 * intervals typically used for benchmarking. Why? First, to
5258 * adapt more quickly to variations. Second, because an I/O
5259 * scheduler cannot rely on a peak-rate-evaluation workload to
5260 * be run for a long time.
5262 T_slow
[0] = msecs_to_jiffies(3500); /* actually 4 sec */
5263 T_slow
[1] = msecs_to_jiffies(6000); /* actually 6.5 sec */
5264 T_fast
[0] = msecs_to_jiffies(7000); /* actually 8 sec */
5265 T_fast
[1] = msecs_to_jiffies(2500); /* actually 3 sec */
5268 * Thresholds that determine the switch between speed classes
5269 * (see the comments before the definition of the array
5270 * device_speed_thresh). These thresholds are biased towards
5271 * transitions to the fast class. This is safer than the
5272 * opposite bias. In fact, a wrong transition to the slow
5273 * class results in short weight-raising periods, because the
5274 * speed of the device then tends to be higher that the
5275 * reference peak rate. On the opposite end, a wrong
5276 * transition to the fast class tends to increase
5277 * weight-raising periods, because of the opposite reason.
5279 device_speed_thresh
[0] = (4 * R_slow
[0]) / 3;
5280 device_speed_thresh
[1] = (4 * R_slow
[1]) / 3;
5282 ret
= elv_register(&iosched_bfq_mq
);
5291 #ifdef CONFIG_BFQ_GROUP_IOSCHED
5292 blkcg_policy_unregister(&blkcg_policy_bfq
);
5297 static void __exit
bfq_exit(void)
5299 elv_unregister(&iosched_bfq_mq
);
5300 #ifdef CONFIG_BFQ_GROUP_IOSCHED
5301 blkcg_policy_unregister(&blkcg_policy_bfq
);
5306 module_init(bfq_init
);
5307 module_exit(bfq_exit
);
5309 MODULE_AUTHOR("Paolo Valente");
5310 MODULE_LICENSE("GPL");
5311 MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");