net/sched/sch_pie.c

   1 /* Copyright (C) 2013 Cisco Systems, Inc, 2013.
   2  *
   3  * This program is free software; you can redistribute it and/or
   4  * modify it under the terms of the GNU General Public License
   5  * as published by the Free Software Foundation; either version 2
   6  * of the License.
   7  *
   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
  11  * GNU General Public License for more details.
  12  *
  13  * Author: Vijay Subramanian <vijaynsu@cisco.com>
  14  * Author: Mythili Prabhu <mysuryan@cisco.com>
  15  *
  16  * ECN support is added by Naeem Khademi <naeemk@ifi.uio.no>
  17  * University of Oslo, Norway.
  18  *
  19  * References:
  20  * IETF draft submission: http://tools.ietf.org/html/draft-pan-aqm-pie-00
  21  * IEEE  Conference on High Performance Switching and Routing 2013 :
  22  * "PIE: A * Lightweight Control Scheme to Address the Bufferbloat Problem"
  23  */
  24
  25 #include <linux/module.h>
  26 #include <linux/slab.h>
  27 #include <linux/types.h>
  28 #include <linux/kernel.h>
  29 #include <linux/errno.h>
  30 #include <linux/skbuff.h>
  31 #include <net/pkt_sched.h>
  32 #include <net/inet_ecn.h>
  33
  34 #define QUEUE_THRESHOLD 10000
  35 #define DQCOUNT_INVALID -1
  36 #define MAX_PROB  0xffffffff
  37 #define PIE_SCALE 8
  38
  39 /* parameters used */
  40 struct pie_params {
  41         psched_time_t target;   /* user specified target delay in pschedtime */
  42         u32 tupdate;            /* timer frequency (in jiffies) */
  43         u32 limit;              /* number of packets that can be enqueued */
  44         u32 alpha;              /* alpha and beta are between 0 and 32 */
  45         u32 beta;               /* and are used for shift relative to 1 */
  46         bool ecn;               /* true if ecn is enabled */
  47         bool bytemode;          /* to scale drop early prob based on pkt size */
  48 };
  49
  50 /* variables used */
  51 struct pie_vars {
  52         u32 prob;               /* probability but scaled by u32 limit. */
  53         psched_time_t burst_time;
  54         psched_time_t qdelay;
  55         psched_time_t qdelay_old;
  56         u64 dq_count;           /* measured in bytes */
  57         psched_time_t dq_tstamp;        /* drain rate */
  58         u32 avg_dq_rate;        /* bytes per pschedtime tick,scaled */
  59         u32 qlen_old;           /* in bytes */
  60 };
  61
  62 /* statistics gathering */
  63 struct pie_stats {
  64         u32 packets_in;         /* total number of packets enqueued */
  65         u32 dropped;            /* packets dropped due to pie_action */
  66         u32 overlimit;          /* dropped due to lack of space in queue */
  67         u32 maxq;               /* maximum queue size */
  68         u32 ecn_mark;           /* packets marked with ECN */
  69 };
  70
  71 /* private data for the Qdisc */
  72 struct pie_sched_data {
  73         struct pie_params params;
  74         struct pie_vars vars;
  75         struct pie_stats stats;
  76         struct timer_list adapt_timer;
  77 };
  78
  79 static void pie_params_init(struct pie_params *params)
  80 {
  81         params->alpha = 2;
  82         params->beta = 20;
  83         params->tupdate = usecs_to_jiffies(30 * USEC_PER_MSEC); /* 30 ms */
  84         params->limit = 1000;   /* default of 1000 packets */
  85         params->target = PSCHED_NS2TICKS(20 * NSEC_PER_MSEC);   /* 20 ms */
  86         params->ecn = false;
  87         params->bytemode = false;
  88 }
  89
  90 static void pie_vars_init(struct pie_vars *vars)
  91 {
  92         vars->dq_count = DQCOUNT_INVALID;
  93         vars->avg_dq_rate = 0;
  94         /* default of 100 ms in pschedtime */
  95         vars->burst_time = PSCHED_NS2TICKS(100 * NSEC_PER_MSEC);
  96 }
  97
  98 static bool drop_early(struct Qdisc *sch, u32 packet_size)
  99 {
 100         struct pie_sched_data *q = qdisc_priv(sch);
 101         u32 rnd;
 102         u32 local_prob = q->vars.prob;
 103         u32 mtu = psched_mtu(qdisc_dev(sch));
 104
 105         /* If there is still burst allowance left skip random early drop */
 106         if (q->vars.burst_time > 0)
 107                 return false;
 108
 109         /* If current delay is less than half of target, and
 110          * if drop prob is low already, disable early_drop
 111          */
 112         if ((q->vars.qdelay < q->params.target / 2)
 113             && (q->vars.prob < MAX_PROB / 5))
 114                 return false;
 115
 116         /* If we have fewer than 2 mtu-sized packets, disable drop_early,
 117          * similar to min_th in RED
 118          */
 119         if (sch->qstats.backlog < 2 * mtu)
 120                 return false;
 121
 122         /* If bytemode is turned on, use packet size to compute new
 123          * probablity. Smaller packets will have lower drop prob in this case
 124          */
 125         if (q->params.bytemode && packet_size <= mtu)
 126                 local_prob = (local_prob / mtu) * packet_size;
 127         else
 128                 local_prob = q->vars.prob;
 129
 130         rnd = prandom_u32();
 131         if (rnd < local_prob)
 132                 return true;
 133
 134         return false;
 135 }
 136
 137 static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 138 {
 139         struct pie_sched_data *q = qdisc_priv(sch);
 140         bool enqueue = false;
 141
 142         if (unlikely(qdisc_qlen(sch) >= sch->limit)) {
 143                 q->stats.overlimit++;
 144                 goto out;
 145         }
 146
 147         if (!drop_early(sch, skb->len)) {
 148                 enqueue = true;
 149         } else if (q->params.ecn && (q->vars.prob <= MAX_PROB / 10) &&
 150                    INET_ECN_set_ce(skb)) {
 151                 /* If packet is ecn capable, mark it if drop probability
 152                  * is lower than 10%, else drop it.
 153                  */
 154                 q->stats.ecn_mark++;
 155                 enqueue = true;
 156         }
 157
 158         /* we can enqueue the packet */
 159         if (enqueue) {
 160                 q->stats.packets_in++;
 161                 if (qdisc_qlen(sch) > q->stats.maxq)
 162                         q->stats.maxq = qdisc_qlen(sch);
 163
 164                 return qdisc_enqueue_tail(skb, sch);
 165         }
 166
 167 out:
 168         q->stats.dropped++;
 169         return qdisc_drop(skb, sch);
 170 }
 171
 172 static const struct nla_policy pie_policy[TCA_PIE_MAX + 1] = {
 173         [TCA_PIE_TARGET] = {.type = NLA_U32},
 174         [TCA_PIE_LIMIT] = {.type = NLA_U32},
 175         [TCA_PIE_TUPDATE] = {.type = NLA_U32},
 176         [TCA_PIE_ALPHA] = {.type = NLA_U32},
 177         [TCA_PIE_BETA] = {.type = NLA_U32},
 178         [TCA_PIE_ECN] = {.type = NLA_U32},
 179         [TCA_PIE_BYTEMODE] = {.type = NLA_U32},
 180 };
 181
 182 static int pie_change(struct Qdisc *sch, struct nlattr *opt)
 183 {
 184         struct pie_sched_data *q = qdisc_priv(sch);
 185         struct nlattr *tb[TCA_PIE_MAX + 1];
 186         unsigned int qlen;
 187         int err;
 188
 189         if (!opt)
 190                 return -EINVAL;
 191
 192         err = nla_parse_nested(tb, TCA_PIE_MAX, opt, pie_policy);
 193         if (err < 0)
 194                 return err;
 195
 196         sch_tree_lock(sch);
 197
 198         /* convert from microseconds to pschedtime */
 199         if (tb[TCA_PIE_TARGET]) {
 200                 /* target is in us */
 201                 u32 target = nla_get_u32(tb[TCA_PIE_TARGET]);
 202
 203                 /* convert to pschedtime */
 204                 q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC);
 205         }
 206
 207         /* tupdate is in jiffies */
 208         if (tb[TCA_PIE_TUPDATE])
 209                 q->params.tupdate = usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE]));
 210
 211         if (tb[TCA_PIE_LIMIT]) {
 212                 u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]);
 213
 214                 q->params.limit = limit;
 215                 sch->limit = limit;
 216         }
 217
 218         if (tb[TCA_PIE_ALPHA])
 219                 q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]);
 220
 221         if (tb[TCA_PIE_BETA])
 222                 q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]);
 223
 224         if (tb[TCA_PIE_ECN])
 225                 q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]);
 226
 227         if (tb[TCA_PIE_BYTEMODE])
 228                 q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]);
 229
 230         /* Drop excess packets if new limit is lower */
 231         qlen = sch->q.qlen;
 232         while (sch->q.qlen > sch->limit) {
 233                 struct sk_buff *skb = __skb_dequeue(&sch->q);
 234
 235                 qdisc_qstats_backlog_dec(sch, skb);
 236                 qdisc_drop(skb, sch);
 237         }
 238         qdisc_tree_decrease_qlen(sch, qlen - sch->q.qlen);
 239
 240         sch_tree_unlock(sch);
 241         return 0;
 242 }
 243
 244 static void pie_process_dequeue(struct Qdisc *sch, struct sk_buff *skb)
 245 {
 246
 247         struct pie_sched_data *q = qdisc_priv(sch);
 248         int qlen = sch->qstats.backlog; /* current queue size in bytes */
 249
 250         /* If current queue is about 10 packets or more and dq_count is unset
 251          * we have enough packets to calculate the drain rate. Save
 252          * current time as dq_tstamp and start measurement cycle.
 253          */
 254         if (qlen >= QUEUE_THRESHOLD && q->vars.dq_count == DQCOUNT_INVALID) {
 255                 q->vars.dq_tstamp = psched_get_time();
 256                 q->vars.dq_count = 0;
 257         }
 258
 259         /* Calculate the average drain rate from this value.  If queue length
 260          * has receded to a small value viz., <= QUEUE_THRESHOLD bytes,reset
 261          * the dq_count to -1 as we don't have enough packets to calculate the
 262          * drain rate anymore The following if block is entered only when we
 263          * have a substantial queue built up (QUEUE_THRESHOLD bytes or more)
 264          * and we calculate the drain rate for the threshold here.  dq_count is
 265          * in bytes, time difference in psched_time, hence rate is in
 266          * bytes/psched_time.
 267          */
 268         if (q->vars.dq_count != DQCOUNT_INVALID) {
 269                 q->vars.dq_count += skb->len;
 270
 271                 if (q->vars.dq_count >= QUEUE_THRESHOLD) {
 272                         psched_time_t now = psched_get_time();
 273                         u32 dtime = now - q->vars.dq_tstamp;
 274                         u32 count = q->vars.dq_count << PIE_SCALE;
 275
 276                         if (dtime == 0)
 277                                 return;
 278
 279                         count = count / dtime;
 280
 281                         if (q->vars.avg_dq_rate == 0)
 282                                 q->vars.avg_dq_rate = count;
 283                         else
 284                                 q->vars.avg_dq_rate =
 285                                     (q->vars.avg_dq_rate -
 286                                      (q->vars.avg_dq_rate >> 3)) + (count >> 3);
 287
 288                         /* If the queue has receded below the threshold, we hold
 289                          * on to the last drain rate calculated, else we reset
 290                          * dq_count to 0 to re-enter the if block when the next
 291                          * packet is dequeued
 292                          */
 293                         if (qlen < QUEUE_THRESHOLD)
 294                                 q->vars.dq_count = DQCOUNT_INVALID;
 295                         else {
 296                                 q->vars.dq_count = 0;
 297                                 q->vars.dq_tstamp = psched_get_time();
 298                         }
 299
 300                         if (q->vars.burst_time > 0) {
 301                                 if (q->vars.burst_time > dtime)
 302                                         q->vars.burst_time -= dtime;
 303                                 else
 304                                         q->vars.burst_time = 0;
 305                         }
 306                 }
 307         }
 308 }
 309
 310 static void calculate_probability(struct Qdisc *sch)
 311 {
 312         struct pie_sched_data *q = qdisc_priv(sch);
 313         u32 qlen = sch->qstats.backlog; /* queue size in bytes */
 314         psched_time_t qdelay = 0;       /* in pschedtime */
 315         psched_time_t qdelay_old = q->vars.qdelay;      /* in pschedtime */
 316         s32 delta = 0;          /* determines the change in probability */
 317         u32 oldprob;
 318         u32 alpha, beta;
 319         bool update_prob = true;
 320
 321         q->vars.qdelay_old = q->vars.qdelay;
 322
 323         if (q->vars.avg_dq_rate > 0)
 324                 qdelay = (qlen << PIE_SCALE) / q->vars.avg_dq_rate;
 325         else
 326                 qdelay = 0;
 327
 328         /* If qdelay is zero and qlen is not, it means qlen is very small, less
 329          * than dequeue_rate, so we do not update probabilty in this round
 330          */
 331         if (qdelay == 0 && qlen != 0)
 332                 update_prob = false;
 333
 334         /* In the algorithm, alpha and beta are between 0 and 2 with typical
 335          * value for alpha as 0.125. In this implementation, we use values 0-32
 336          * passed from user space to represent this. Also, alpha and beta have
 337          * unit of HZ and need to be scaled before they can used to update
 338          * probability. alpha/beta are updated locally below by 1) scaling them
 339          * appropriately 2) scaling down by 16 to come to 0-2 range.
 340          * Please see paper for details.
 341          *
 342          * We scale alpha and beta differently depending on whether we are in
 343          * light, medium or high dropping mode.
 344          */
 345         if (q->vars.prob < MAX_PROB / 100) {
 346                 alpha =
 347                     (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
 348                 beta =
 349                     (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
 350         } else if (q->vars.prob < MAX_PROB / 10) {
 351                 alpha =
 352                     (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
 353                 beta =
 354                     (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
 355         } else {
 356                 alpha =
 357                     (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
 358                 beta =
 359                     (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
 360         }
 361
 362         /* alpha and beta should be between 0 and 32, in multiples of 1/16 */
 363         delta += alpha * ((qdelay - q->params.target));
 364         delta += beta * ((qdelay - qdelay_old));
 365
 366         oldprob = q->vars.prob;
 367
 368         /* to ensure we increase probability in steps of no more than 2% */
 369         if (delta > (s32) (MAX_PROB / (100 / 2)) &&
 370             q->vars.prob >= MAX_PROB / 10)
 371                 delta = (MAX_PROB / 100) * 2;
 372
 373         /* Non-linear drop:
 374          * Tune drop probability to increase quickly for high delays(>= 250ms)
 375          * 250ms is derived through experiments and provides error protection
 376          */
 377
 378         if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC)))
 379                 delta += MAX_PROB / (100 / 2);
 380
 381         q->vars.prob += delta;
 382
 383         if (delta > 0) {
 384                 /* prevent overflow */
 385                 if (q->vars.prob < oldprob) {
 386                         q->vars.prob = MAX_PROB;
 387                         /* Prevent normalization error. If probability is at
 388                          * maximum value already, we normalize it here, and
 389                          * skip the check to do a non-linear drop in the next
 390                          * section.
 391                          */
 392                         update_prob = false;
 393                 }
 394         } else {
 395                 /* prevent underflow */
 396                 if (q->vars.prob > oldprob)
 397                         q->vars.prob = 0;
 398         }
 399
 400         /* Non-linear drop in probability: Reduce drop probability quickly if
 401          * delay is 0 for 2 consecutive Tupdate periods.
 402          */
 403
 404         if ((qdelay == 0) && (qdelay_old == 0) && update_prob)
 405                 q->vars.prob = (q->vars.prob * 98) / 100;
 406
 407         q->vars.qdelay = qdelay;
 408         q->vars.qlen_old = qlen;
 409
 410         /* We restart the measurement cycle if the following conditions are met
 411          * 1. If the delay has been low for 2 consecutive Tupdate periods
 412          * 2. Calculated drop probability is zero
 413          * 3. We have atleast one estimate for the avg_dq_rate ie.,
 414          *    is a non-zero value
 415          */
 416         if ((q->vars.qdelay < q->params.target / 2) &&
 417             (q->vars.qdelay_old < q->params.target / 2) &&
 418             (q->vars.prob == 0) &&
 419             (q->vars.avg_dq_rate > 0))
 420                 pie_vars_init(&q->vars);
 421 }
 422
 423 static void pie_timer(unsigned long arg)
 424 {
 425         struct Qdisc *sch = (struct Qdisc *)arg;
 426         struct pie_sched_data *q = qdisc_priv(sch);
 427         spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch));
 428
 429         spin_lock(root_lock);
 430         calculate_probability(sch);
 431
 432         /* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */
 433         if (q->params.tupdate)
 434                 mod_timer(&q->adapt_timer, jiffies + q->params.tupdate);
 435         spin_unlock(root_lock);
 436
 437 }
 438
 439 static int pie_init(struct Qdisc *sch, struct nlattr *opt)
 440 {
 441         struct pie_sched_data *q = qdisc_priv(sch);
 442
 443         pie_params_init(&q->params);
 444         pie_vars_init(&q->vars);
 445         sch->limit = q->params.limit;
 446
 447         setup_timer(&q->adapt_timer, pie_timer, (unsigned long)sch);
 448
 449         if (opt) {
 450                 int err = pie_change(sch, opt);
 451
 452                 if (err)
 453                         return err;
 454         }
 455
 456         mod_timer(&q->adapt_timer, jiffies + HZ / 2);
 457         return 0;
 458 }
 459
 460 static int pie_dump(struct Qdisc *sch, struct sk_buff *skb)
 461 {
 462         struct pie_sched_data *q = qdisc_priv(sch);
 463         struct nlattr *opts;
 464
 465         opts = nla_nest_start(skb, TCA_OPTIONS);
 466         if (opts == NULL)
 467                 goto nla_put_failure;
 468
 469         /* convert target from pschedtime to us */
 470         if (nla_put_u32(skb, TCA_PIE_TARGET,
 471                         ((u32) PSCHED_TICKS2NS(q->params.target)) /
 472                         NSEC_PER_USEC) ||
 473             nla_put_u32(skb, TCA_PIE_LIMIT, sch->limit) ||
 474             nla_put_u32(skb, TCA_PIE_TUPDATE, jiffies_to_usecs(q->params.tupdate)) ||
 475             nla_put_u32(skb, TCA_PIE_ALPHA, q->params.alpha) ||
 476             nla_put_u32(skb, TCA_PIE_BETA, q->params.beta) ||
 477             nla_put_u32(skb, TCA_PIE_ECN, q->params.ecn) ||
 478             nla_put_u32(skb, TCA_PIE_BYTEMODE, q->params.bytemode))
 479                 goto nla_put_failure;
 480
 481         return nla_nest_end(skb, opts);
 482
 483 nla_put_failure:
 484         nla_nest_cancel(skb, opts);
 485         return -1;
 486
 487 }
 488
 489 static int pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 490 {
 491         struct pie_sched_data *q = qdisc_priv(sch);
 492         struct tc_pie_xstats st = {
 493                 .prob           = q->vars.prob,
 494                 .delay          = ((u32) PSCHED_TICKS2NS(q->vars.qdelay)) /
 495                                    NSEC_PER_USEC,
 496                 /* unscale and return dq_rate in bytes per sec */
 497                 .avg_dq_rate    = q->vars.avg_dq_rate *
 498                                   (PSCHED_TICKS_PER_SEC) >> PIE_SCALE,
 499                 .packets_in     = q->stats.packets_in,
 500                 .overlimit      = q->stats.overlimit,
 501                 .maxq           = q->stats.maxq,
 502                 .dropped        = q->stats.dropped,
 503                 .ecn_mark       = q->stats.ecn_mark,
 504         };
 505
 506         return gnet_stats_copy_app(d, &st, sizeof(st));
 507 }
 508
 509 static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch)
 510 {
 511         struct sk_buff *skb;
 512         skb = __qdisc_dequeue_head(sch, &sch->q);
 513
 514         if (!skb)
 515                 return NULL;
 516
 517         pie_process_dequeue(sch, skb);
 518         return skb;
 519 }
 520
 521 static void pie_reset(struct Qdisc *sch)
 522 {
 523         struct pie_sched_data *q = qdisc_priv(sch);
 524         qdisc_reset_queue(sch);
 525         pie_vars_init(&q->vars);
 526 }
 527
 528 static void pie_destroy(struct Qdisc *sch)
 529 {
 530         struct pie_sched_data *q = qdisc_priv(sch);
 531         q->params.tupdate = 0;
 532         del_timer_sync(&q->adapt_timer);
 533 }
 534
 535 static struct Qdisc_ops pie_qdisc_ops __read_mostly = {
 536         .id = "pie",
 537         .priv_size      = sizeof(struct pie_sched_data),
 538         .enqueue        = pie_qdisc_enqueue,
 539         .dequeue        = pie_qdisc_dequeue,
 540         .peek           = qdisc_peek_dequeued,
 541         .init           = pie_init,
 542         .destroy        = pie_destroy,
 543         .reset          = pie_reset,
 544         .change         = pie_change,
 545         .dump           = pie_dump,
 546         .dump_stats     = pie_dump_stats,
 547         .owner          = THIS_MODULE,
 548 };
 549
 550 static int __init pie_module_init(void)
 551 {
 552         return register_qdisc(&pie_qdisc_ops);
 553 }
 554
 555 static void __exit pie_module_exit(void)
 556 {
 557         unregister_qdisc(&pie_qdisc_ops);
 558 }
 559
 560 module_init(pie_module_init);
 561 module_exit(pie_module_exit);
 562
 563 MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler");
 564 MODULE_AUTHOR("Vijay Subramanian");
 565 MODULE_AUTHOR("Mythili Prabhu");
 566 MODULE_LICENSE("GPL");