2 * Copyright (C) 2007 Oracle. All rights reserved.
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public
6 * License v2 as published by the Free Software Foundation.
8 * This program is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
11 * General Public License for more details.
13 * You should have received a copy of the GNU General Public
14 * License along with this program; if not, write to the
15 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
16 * Boston, MA 021110-1307, USA.
19 #include <linux/kthread.h>
20 #include <linux/slab.h>
21 #include <linux/list.h>
22 #include <linux/spinlock.h>
23 #include <linux/freezer.h>
24 #include "async-thread.h"
26 #define WORK_QUEUED_BIT 0
27 #define WORK_DONE_BIT 1
28 #define WORK_ORDER_DONE_BIT 2
29 #define WORK_HIGH_PRIO_BIT 3
32 * container for the kthread task pointer and the list of pending work
33 * One of these is allocated per thread.
35 struct btrfs_worker_thread
{
36 /* pool we belong to */
37 struct btrfs_workers
*workers
;
39 /* list of struct btrfs_work that are waiting for service */
40 struct list_head pending
;
41 struct list_head prio_pending
;
43 /* list of worker threads from struct btrfs_workers */
44 struct list_head worker_list
;
47 struct task_struct
*task
;
49 /* number of things on the pending list */
52 /* reference counter for this struct */
55 unsigned long sequence
;
57 /* protects the pending list. */
60 /* set to non-zero when this thread is already awake and kicking */
63 /* are we currently idle */
67 static int __btrfs_start_workers(struct btrfs_workers
*workers
);
70 * btrfs_start_workers uses kthread_run, which can block waiting for memory
71 * for a very long time. It will actually throttle on page writeback,
72 * and so it may not make progress until after our btrfs worker threads
73 * process all of the pending work structs in their queue
75 * This means we can't use btrfs_start_workers from inside a btrfs worker
76 * thread that is used as part of cleaning dirty memory, which pretty much
77 * involves all of the worker threads.
79 * Instead we have a helper queue who never has more than one thread
80 * where we scheduler thread start operations. This worker_start struct
81 * is used to contain the work and hold a pointer to the queue that needs
85 struct btrfs_work work
;
86 struct btrfs_workers
*queue
;
89 static void start_new_worker_func(struct btrfs_work
*work
)
91 struct worker_start
*start
;
92 start
= container_of(work
, struct worker_start
, work
);
93 __btrfs_start_workers(start
->queue
);
98 * helper function to move a thread onto the idle list after it
99 * has finished some requests.
101 static void check_idle_worker(struct btrfs_worker_thread
*worker
)
103 if (!worker
->idle
&& atomic_read(&worker
->num_pending
) <
104 worker
->workers
->idle_thresh
/ 2) {
106 spin_lock_irqsave(&worker
->workers
->lock
, flags
);
109 /* the list may be empty if the worker is just starting */
110 if (!list_empty(&worker
->worker_list
) &&
111 !worker
->workers
->stopping
) {
112 list_move(&worker
->worker_list
,
113 &worker
->workers
->idle_list
);
115 spin_unlock_irqrestore(&worker
->workers
->lock
, flags
);
120 * helper function to move a thread off the idle list after new
121 * pending work is added.
123 static void check_busy_worker(struct btrfs_worker_thread
*worker
)
125 if (worker
->idle
&& atomic_read(&worker
->num_pending
) >=
126 worker
->workers
->idle_thresh
) {
128 spin_lock_irqsave(&worker
->workers
->lock
, flags
);
131 if (!list_empty(&worker
->worker_list
) &&
132 !worker
->workers
->stopping
) {
133 list_move_tail(&worker
->worker_list
,
134 &worker
->workers
->worker_list
);
136 spin_unlock_irqrestore(&worker
->workers
->lock
, flags
);
140 static void check_pending_worker_creates(struct btrfs_worker_thread
*worker
)
142 struct btrfs_workers
*workers
= worker
->workers
;
143 struct worker_start
*start
;
147 if (!workers
->atomic_start_pending
)
150 start
= kzalloc(sizeof(*start
), GFP_NOFS
);
154 start
->work
.func
= start_new_worker_func
;
155 start
->queue
= workers
;
157 spin_lock_irqsave(&workers
->lock
, flags
);
158 if (!workers
->atomic_start_pending
)
161 workers
->atomic_start_pending
= 0;
162 if (workers
->num_workers
+ workers
->num_workers_starting
>=
163 workers
->max_workers
)
166 workers
->num_workers_starting
+= 1;
167 spin_unlock_irqrestore(&workers
->lock
, flags
);
168 btrfs_queue_worker(workers
->atomic_worker_start
, &start
->work
);
173 spin_unlock_irqrestore(&workers
->lock
, flags
);
176 static noinline
void run_ordered_completions(struct btrfs_workers
*workers
,
177 struct btrfs_work
*work
)
179 if (!workers
->ordered
)
182 set_bit(WORK_DONE_BIT
, &work
->flags
);
184 spin_lock(&workers
->order_lock
);
187 if (!list_empty(&workers
->prio_order_list
)) {
188 work
= list_entry(workers
->prio_order_list
.next
,
189 struct btrfs_work
, order_list
);
190 } else if (!list_empty(&workers
->order_list
)) {
191 work
= list_entry(workers
->order_list
.next
,
192 struct btrfs_work
, order_list
);
196 if (!test_bit(WORK_DONE_BIT
, &work
->flags
))
199 /* we are going to call the ordered done function, but
200 * we leave the work item on the list as a barrier so
201 * that later work items that are done don't have their
202 * functions called before this one returns
204 if (test_and_set_bit(WORK_ORDER_DONE_BIT
, &work
->flags
))
207 spin_unlock(&workers
->order_lock
);
209 work
->ordered_func(work
);
211 /* now take the lock again and drop our item from the list */
212 spin_lock(&workers
->order_lock
);
213 list_del(&work
->order_list
);
214 spin_unlock(&workers
->order_lock
);
217 * we don't want to call the ordered free functions
218 * with the lock held though
220 work
->ordered_free(work
);
221 spin_lock(&workers
->order_lock
);
224 spin_unlock(&workers
->order_lock
);
227 static void put_worker(struct btrfs_worker_thread
*worker
)
229 if (atomic_dec_and_test(&worker
->refs
))
233 static int try_worker_shutdown(struct btrfs_worker_thread
*worker
)
237 spin_lock_irq(&worker
->lock
);
238 spin_lock(&worker
->workers
->lock
);
239 if (worker
->workers
->num_workers
> 1 &&
242 !list_empty(&worker
->worker_list
) &&
243 list_empty(&worker
->prio_pending
) &&
244 list_empty(&worker
->pending
) &&
245 atomic_read(&worker
->num_pending
) == 0) {
247 list_del_init(&worker
->worker_list
);
248 worker
->workers
->num_workers
--;
250 spin_unlock(&worker
->workers
->lock
);
251 spin_unlock_irq(&worker
->lock
);
258 static struct btrfs_work
*get_next_work(struct btrfs_worker_thread
*worker
,
259 struct list_head
*prio_head
,
260 struct list_head
*head
)
262 struct btrfs_work
*work
= NULL
;
263 struct list_head
*cur
= NULL
;
265 if(!list_empty(prio_head
))
266 cur
= prio_head
->next
;
269 if (!list_empty(&worker
->prio_pending
))
272 if (!list_empty(head
))
279 spin_lock_irq(&worker
->lock
);
280 list_splice_tail_init(&worker
->prio_pending
, prio_head
);
281 list_splice_tail_init(&worker
->pending
, head
);
283 if (!list_empty(prio_head
))
284 cur
= prio_head
->next
;
285 else if (!list_empty(head
))
287 spin_unlock_irq(&worker
->lock
);
293 work
= list_entry(cur
, struct btrfs_work
, list
);
300 * main loop for servicing work items
302 static int worker_loop(void *arg
)
304 struct btrfs_worker_thread
*worker
= arg
;
305 struct list_head head
;
306 struct list_head prio_head
;
307 struct btrfs_work
*work
;
309 INIT_LIST_HEAD(&head
);
310 INIT_LIST_HEAD(&prio_head
);
317 work
= get_next_work(worker
, &prio_head
, &head
);
321 list_del(&work
->list
);
322 clear_bit(WORK_QUEUED_BIT
, &work
->flags
);
324 work
->worker
= worker
;
328 atomic_dec(&worker
->num_pending
);
330 * unless this is an ordered work queue,
331 * 'work' was probably freed by func above.
333 run_ordered_completions(worker
->workers
, work
);
335 check_pending_worker_creates(worker
);
339 spin_lock_irq(&worker
->lock
);
340 check_idle_worker(worker
);
342 if (freezing(current
)) {
344 spin_unlock_irq(&worker
->lock
);
347 spin_unlock_irq(&worker
->lock
);
348 if (!kthread_should_stop()) {
351 * we've dropped the lock, did someone else
355 if (!list_empty(&worker
->pending
) ||
356 !list_empty(&worker
->prio_pending
))
360 * this short schedule allows more work to
361 * come in without the queue functions
362 * needing to go through wake_up_process()
364 * worker->working is still 1, so nobody
365 * is going to try and wake us up
369 if (!list_empty(&worker
->pending
) ||
370 !list_empty(&worker
->prio_pending
))
373 if (kthread_should_stop())
376 /* still no more work?, sleep for real */
377 spin_lock_irq(&worker
->lock
);
378 set_current_state(TASK_INTERRUPTIBLE
);
379 if (!list_empty(&worker
->pending
) ||
380 !list_empty(&worker
->prio_pending
)) {
381 spin_unlock_irq(&worker
->lock
);
382 set_current_state(TASK_RUNNING
);
387 * this makes sure we get a wakeup when someone
388 * adds something new to the queue
391 spin_unlock_irq(&worker
->lock
);
393 if (!kthread_should_stop()) {
394 schedule_timeout(HZ
* 120);
395 if (!worker
->working
&&
396 try_worker_shutdown(worker
)) {
401 __set_current_state(TASK_RUNNING
);
403 } while (!kthread_should_stop());
408 * this will wait for all the worker threads to shutdown
410 void btrfs_stop_workers(struct btrfs_workers
*workers
)
412 struct list_head
*cur
;
413 struct btrfs_worker_thread
*worker
;
416 spin_lock_irq(&workers
->lock
);
417 workers
->stopping
= 1;
418 list_splice_init(&workers
->idle_list
, &workers
->worker_list
);
419 while (!list_empty(&workers
->worker_list
)) {
420 cur
= workers
->worker_list
.next
;
421 worker
= list_entry(cur
, struct btrfs_worker_thread
,
424 atomic_inc(&worker
->refs
);
425 workers
->num_workers
-= 1;
426 if (!list_empty(&worker
->worker_list
)) {
427 list_del_init(&worker
->worker_list
);
432 spin_unlock_irq(&workers
->lock
);
434 kthread_stop(worker
->task
);
435 spin_lock_irq(&workers
->lock
);
438 spin_unlock_irq(&workers
->lock
);
442 * simple init on struct btrfs_workers
444 void btrfs_init_workers(struct btrfs_workers
*workers
, char *name
, int max
,
445 struct btrfs_workers
*async_helper
)
447 workers
->num_workers
= 0;
448 workers
->num_workers_starting
= 0;
449 INIT_LIST_HEAD(&workers
->worker_list
);
450 INIT_LIST_HEAD(&workers
->idle_list
);
451 INIT_LIST_HEAD(&workers
->order_list
);
452 INIT_LIST_HEAD(&workers
->prio_order_list
);
453 spin_lock_init(&workers
->lock
);
454 spin_lock_init(&workers
->order_lock
);
455 workers
->max_workers
= max
;
456 workers
->idle_thresh
= 32;
457 workers
->name
= name
;
458 workers
->ordered
= 0;
459 workers
->atomic_start_pending
= 0;
460 workers
->atomic_worker_start
= async_helper
;
461 workers
->stopping
= 0;
465 * starts new worker threads. This does not enforce the max worker
466 * count in case you need to temporarily go past it.
468 static int __btrfs_start_workers(struct btrfs_workers
*workers
)
470 struct btrfs_worker_thread
*worker
;
473 worker
= kzalloc(sizeof(*worker
), GFP_NOFS
);
479 INIT_LIST_HEAD(&worker
->pending
);
480 INIT_LIST_HEAD(&worker
->prio_pending
);
481 INIT_LIST_HEAD(&worker
->worker_list
);
482 spin_lock_init(&worker
->lock
);
484 atomic_set(&worker
->num_pending
, 0);
485 atomic_set(&worker
->refs
, 1);
486 worker
->workers
= workers
;
487 worker
->task
= kthread_create(worker_loop
, worker
,
488 "btrfs-%s-%d", workers
->name
,
489 workers
->num_workers
+ 1);
490 if (IS_ERR(worker
->task
)) {
491 ret
= PTR_ERR(worker
->task
);
495 spin_lock_irq(&workers
->lock
);
496 if (workers
->stopping
) {
497 spin_unlock_irq(&workers
->lock
);
500 list_add_tail(&worker
->worker_list
, &workers
->idle_list
);
502 workers
->num_workers
++;
503 workers
->num_workers_starting
--;
504 WARN_ON(workers
->num_workers_starting
< 0);
505 spin_unlock_irq(&workers
->lock
);
507 wake_up_process(worker
->task
);
511 kthread_stop(worker
->task
);
514 spin_lock_irq(&workers
->lock
);
515 workers
->num_workers_starting
--;
516 spin_unlock_irq(&workers
->lock
);
520 int btrfs_start_workers(struct btrfs_workers
*workers
)
522 spin_lock_irq(&workers
->lock
);
523 workers
->num_workers_starting
++;
524 spin_unlock_irq(&workers
->lock
);
525 return __btrfs_start_workers(workers
);
529 * run through the list and find a worker thread that doesn't have a lot
530 * to do right now. This can return null if we aren't yet at the thread
531 * count limit and all of the threads are busy.
533 static struct btrfs_worker_thread
*next_worker(struct btrfs_workers
*workers
)
535 struct btrfs_worker_thread
*worker
;
536 struct list_head
*next
;
539 enforce_min
= (workers
->num_workers
+ workers
->num_workers_starting
) <
540 workers
->max_workers
;
543 * if we find an idle thread, don't move it to the end of the
544 * idle list. This improves the chance that the next submission
545 * will reuse the same thread, and maybe catch it while it is still
548 if (!list_empty(&workers
->idle_list
)) {
549 next
= workers
->idle_list
.next
;
550 worker
= list_entry(next
, struct btrfs_worker_thread
,
554 if (enforce_min
|| list_empty(&workers
->worker_list
))
558 * if we pick a busy task, move the task to the end of the list.
559 * hopefully this will keep things somewhat evenly balanced.
560 * Do the move in batches based on the sequence number. This groups
561 * requests submitted at roughly the same time onto the same worker.
563 next
= workers
->worker_list
.next
;
564 worker
= list_entry(next
, struct btrfs_worker_thread
, worker_list
);
567 if (worker
->sequence
% workers
->idle_thresh
== 0)
568 list_move_tail(next
, &workers
->worker_list
);
573 * selects a worker thread to take the next job. This will either find
574 * an idle worker, start a new worker up to the max count, or just return
575 * one of the existing busy workers.
577 static struct btrfs_worker_thread
*find_worker(struct btrfs_workers
*workers
)
579 struct btrfs_worker_thread
*worker
;
581 struct list_head
*fallback
;
584 spin_lock_irqsave(&workers
->lock
, flags
);
586 worker
= next_worker(workers
);
589 if (workers
->num_workers
+ workers
->num_workers_starting
>=
590 workers
->max_workers
) {
592 } else if (workers
->atomic_worker_start
) {
593 workers
->atomic_start_pending
= 1;
596 workers
->num_workers_starting
++;
597 spin_unlock_irqrestore(&workers
->lock
, flags
);
598 /* we're below the limit, start another worker */
599 ret
= __btrfs_start_workers(workers
);
600 spin_lock_irqsave(&workers
->lock
, flags
);
611 * we have failed to find any workers, just
612 * return the first one we can find.
614 if (!list_empty(&workers
->worker_list
))
615 fallback
= workers
->worker_list
.next
;
616 if (!list_empty(&workers
->idle_list
))
617 fallback
= workers
->idle_list
.next
;
619 worker
= list_entry(fallback
,
620 struct btrfs_worker_thread
, worker_list
);
623 * this makes sure the worker doesn't exit before it is placed
624 * onto a busy/idle list
626 atomic_inc(&worker
->num_pending
);
627 spin_unlock_irqrestore(&workers
->lock
, flags
);
632 * btrfs_requeue_work just puts the work item back on the tail of the list
633 * it was taken from. It is intended for use with long running work functions
634 * that make some progress and want to give the cpu up for others.
636 void btrfs_requeue_work(struct btrfs_work
*work
)
638 struct btrfs_worker_thread
*worker
= work
->worker
;
642 if (test_and_set_bit(WORK_QUEUED_BIT
, &work
->flags
))
645 spin_lock_irqsave(&worker
->lock
, flags
);
646 if (test_bit(WORK_HIGH_PRIO_BIT
, &work
->flags
))
647 list_add_tail(&work
->list
, &worker
->prio_pending
);
649 list_add_tail(&work
->list
, &worker
->pending
);
650 atomic_inc(&worker
->num_pending
);
652 /* by definition we're busy, take ourselves off the idle
656 spin_lock(&worker
->workers
->lock
);
658 list_move_tail(&worker
->worker_list
,
659 &worker
->workers
->worker_list
);
660 spin_unlock(&worker
->workers
->lock
);
662 if (!worker
->working
) {
668 wake_up_process(worker
->task
);
669 spin_unlock_irqrestore(&worker
->lock
, flags
);
672 void btrfs_set_work_high_prio(struct btrfs_work
*work
)
674 set_bit(WORK_HIGH_PRIO_BIT
, &work
->flags
);
678 * places a struct btrfs_work into the pending queue of one of the kthreads
680 void btrfs_queue_worker(struct btrfs_workers
*workers
, struct btrfs_work
*work
)
682 struct btrfs_worker_thread
*worker
;
686 /* don't requeue something already on a list */
687 if (test_and_set_bit(WORK_QUEUED_BIT
, &work
->flags
))
690 worker
= find_worker(workers
);
691 if (workers
->ordered
) {
693 * you're not allowed to do ordered queues from an
696 spin_lock(&workers
->order_lock
);
697 if (test_bit(WORK_HIGH_PRIO_BIT
, &work
->flags
)) {
698 list_add_tail(&work
->order_list
,
699 &workers
->prio_order_list
);
701 list_add_tail(&work
->order_list
, &workers
->order_list
);
703 spin_unlock(&workers
->order_lock
);
705 INIT_LIST_HEAD(&work
->order_list
);
708 spin_lock_irqsave(&worker
->lock
, flags
);
710 if (test_bit(WORK_HIGH_PRIO_BIT
, &work
->flags
))
711 list_add_tail(&work
->list
, &worker
->prio_pending
);
713 list_add_tail(&work
->list
, &worker
->pending
);
714 check_busy_worker(worker
);
717 * avoid calling into wake_up_process if this thread has already
720 if (!worker
->working
)
725 wake_up_process(worker
->task
);
726 spin_unlock_irqrestore(&worker
->lock
, flags
);