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                              struct sk_buff **to_free)
 139 {
 140         struct pie_sched_data *q = qdisc_priv(sch);
 141         bool enqueue = false;
 142
 143         if (unlikely(qdisc_qlen(sch) >= sch->limit)) {
 144                 q->stats.overlimit++;
 145                 goto out;
 146         }
 147
 148         if (!drop_early(sch, skb->len)) {
 149                 enqueue = true;
 150         } else if (q->params.ecn && (q->vars.prob <= MAX_PROB / 10) &&
 151                    INET_ECN_set_ce(skb)) {
 152                 /* If packet is ecn capable, mark it if drop probability
 153                  * is lower than 10%, else drop it.
 154                  */
 155                 q->stats.ecn_mark++;
 156                 enqueue = true;
 157         }
 158
 159         /* we can enqueue the packet */
 160         if (enqueue) {
 161                 q->stats.packets_in++;
 162                 if (qdisc_qlen(sch) > q->stats.maxq)
 163                         q->stats.maxq = qdisc_qlen(sch);
 164
 165                 return qdisc_enqueue_tail(skb, sch);
 166         }
 167
 168 out:
 169         q->stats.dropped++;
 170         return qdisc_drop(skb, sch, to_free);
 171 }
 172
 173 static const struct nla_policy pie_policy[TCA_PIE_MAX + 1] = {
 174         [TCA_PIE_TARGET] = {.type = NLA_U32},
 175         [TCA_PIE_LIMIT] = {.type = NLA_U32},
 176         [TCA_PIE_TUPDATE] = {.type = NLA_U32},
 177         [TCA_PIE_ALPHA] = {.type = NLA_U32},
 178         [TCA_PIE_BETA] = {.type = NLA_U32},
 179         [TCA_PIE_ECN] = {.type = NLA_U32},
 180         [TCA_PIE_BYTEMODE] = {.type = NLA_U32},
 181 };
 182
 183 static int pie_change(struct Qdisc *sch, struct nlattr *opt)
 184 {
 185         struct pie_sched_data *q = qdisc_priv(sch);
 186         struct nlattr *tb[TCA_PIE_MAX + 1];
 187         unsigned int qlen, dropped = 0;
 188         int err;
 189
 190         if (!opt)
 191                 return -EINVAL;
 192
 193         err = nla_parse_nested(tb, TCA_PIE_MAX, opt, pie_policy);
 194         if (err < 0)
 195                 return err;
 196
 197         sch_tree_lock(sch);
 198
 199         /* convert from microseconds to pschedtime */
 200         if (tb[TCA_PIE_TARGET]) {
 201                 /* target is in us */
 202                 u32 target = nla_get_u32(tb[TCA_PIE_TARGET]);
 203
 204                 /* convert to pschedtime */
 205                 q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC);
 206         }
 207
 208         /* tupdate is in jiffies */
 209         if (tb[TCA_PIE_TUPDATE])
 210                 q->params.tupdate = usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE]));
 211
 212         if (tb[TCA_PIE_LIMIT]) {
 213                 u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]);
 214
 215                 q->params.limit = limit;
 216                 sch->limit = limit;
 217         }
 218
 219         if (tb[TCA_PIE_ALPHA])
 220                 q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]);
 221
 222         if (tb[TCA_PIE_BETA])
 223                 q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]);
 224
 225         if (tb[TCA_PIE_ECN])
 226                 q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]);
 227
 228         if (tb[TCA_PIE_BYTEMODE])
 229                 q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]);
 230
 231         /* Drop excess packets if new limit is lower */
 232         qlen = sch->q.qlen;
 233         while (sch->q.qlen > sch->limit) {
 234                 struct sk_buff *skb = __qdisc_dequeue_head(&sch->q);
 235
 236                 dropped += qdisc_pkt_len(skb);
 237                 qdisc_qstats_backlog_dec(sch, skb);
 238                 rtnl_qdisc_drop(skb, sch);
 239         }
 240         qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped);
 241
 242         sch_tree_unlock(sch);
 243         return 0;
 244 }
 245
 246 static void pie_process_dequeue(struct Qdisc *sch, struct sk_buff *skb)
 247 {
 248
 249         struct pie_sched_data *q = qdisc_priv(sch);
 250         int qlen = sch->qstats.backlog; /* current queue size in bytes */
 251
 252         /* If current queue is about 10 packets or more and dq_count is unset
 253          * we have enough packets to calculate the drain rate. Save
 254          * current time as dq_tstamp and start measurement cycle.
 255          */
 256         if (qlen >= QUEUE_THRESHOLD && q->vars.dq_count == DQCOUNT_INVALID) {
 257                 q->vars.dq_tstamp = psched_get_time();
 258                 q->vars.dq_count = 0;
 259         }
 260
 261         /* Calculate the average drain rate from this value.  If queue length
 262          * has receded to a small value viz., <= QUEUE_THRESHOLD bytes,reset
 263          * the dq_count to -1 as we don't have enough packets to calculate the
 264          * drain rate anymore The following if block is entered only when we
 265          * have a substantial queue built up (QUEUE_THRESHOLD bytes or more)
 266          * and we calculate the drain rate for the threshold here.  dq_count is
 267          * in bytes, time difference in psched_time, hence rate is in
 268          * bytes/psched_time.
 269          */
 270         if (q->vars.dq_count != DQCOUNT_INVALID) {
 271                 q->vars.dq_count += skb->len;
 272
 273                 if (q->vars.dq_count >= QUEUE_THRESHOLD) {
 274                         psched_time_t now = psched_get_time();
 275                         u32 dtime = now - q->vars.dq_tstamp;
 276                         u32 count = q->vars.dq_count << PIE_SCALE;
 277
 278                         if (dtime == 0)
 279                                 return;
 280
 281                         count = count / dtime;
 282
 283                         if (q->vars.avg_dq_rate == 0)
 284                                 q->vars.avg_dq_rate = count;
 285                         else
 286                                 q->vars.avg_dq_rate =
 287                                     (q->vars.avg_dq_rate -
 288                                      (q->vars.avg_dq_rate >> 3)) + (count >> 3);
 289
 290                         /* If the queue has receded below the threshold, we hold
 291                          * on to the last drain rate calculated, else we reset
 292                          * dq_count to 0 to re-enter the if block when the next
 293                          * packet is dequeued
 294                          */
 295                         if (qlen < QUEUE_THRESHOLD)
 296                                 q->vars.dq_count = DQCOUNT_INVALID;
 297                         else {
 298                                 q->vars.dq_count = 0;
 299                                 q->vars.dq_tstamp = psched_get_time();
 300                         }
 301
 302                         if (q->vars.burst_time > 0) {
 303                                 if (q->vars.burst_time > dtime)
 304                                         q->vars.burst_time -= dtime;
 305                                 else
 306                                         q->vars.burst_time = 0;
 307                         }
 308                 }
 309         }
 310 }
 311
 312 static void calculate_probability(struct Qdisc *sch)
 313 {
 314         struct pie_sched_data *q = qdisc_priv(sch);
 315         u32 qlen = sch->qstats.backlog; /* queue size in bytes */
 316         psched_time_t qdelay = 0;       /* in pschedtime */
 317         psched_time_t qdelay_old = q->vars.qdelay;      /* in pschedtime */
 318         s32 delta = 0;          /* determines the change in probability */
 319         u32 oldprob;
 320         u32 alpha, beta;
 321         bool update_prob = true;
 322
 323         q->vars.qdelay_old = q->vars.qdelay;
 324
 325         if (q->vars.avg_dq_rate > 0)
 326                 qdelay = (qlen << PIE_SCALE) / q->vars.avg_dq_rate;
 327         else
 328                 qdelay = 0;
 329
 330         /* If qdelay is zero and qlen is not, it means qlen is very small, less
 331          * than dequeue_rate, so we do not update probabilty in this round
 332          */
 333         if (qdelay == 0 && qlen != 0)
 334                 update_prob = false;
 335
 336         /* In the algorithm, alpha and beta are between 0 and 2 with typical
 337          * value for alpha as 0.125. In this implementation, we use values 0-32
 338          * passed from user space to represent this. Also, alpha and beta have
 339          * unit of HZ and need to be scaled before they can used to update
 340          * probability. alpha/beta are updated locally below by 1) scaling them
 341          * appropriately 2) scaling down by 16 to come to 0-2 range.
 342          * Please see paper for details.
 343          *
 344          * We scale alpha and beta differently depending on whether we are in
 345          * light, medium or high dropping mode.
 346          */
 347         if (q->vars.prob < MAX_PROB / 100) {
 348                 alpha =
 349                     (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
 350                 beta =
 351                     (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
 352         } else if (q->vars.prob < MAX_PROB / 10) {
 353                 alpha =
 354                     (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
 355                 beta =
 356                     (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
 357         } else {
 358                 alpha =
 359                     (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
 360                 beta =
 361                     (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
 362         }
 363
 364         /* alpha and beta should be between 0 and 32, in multiples of 1/16 */
 365         delta += alpha * ((qdelay - q->params.target));
 366         delta += beta * ((qdelay - qdelay_old));
 367
 368         oldprob = q->vars.prob;
 369
 370         /* to ensure we increase probability in steps of no more than 2% */
 371         if (delta > (s32) (MAX_PROB / (100 / 2)) &&
 372             q->vars.prob >= MAX_PROB / 10)
 373                 delta = (MAX_PROB / 100) * 2;
 374
 375         /* Non-linear drop:
 376          * Tune drop probability to increase quickly for high delays(>= 250ms)
 377          * 250ms is derived through experiments and provides error protection
 378          */
 379
 380         if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC)))
 381                 delta += MAX_PROB / (100 / 2);
 382
 383         q->vars.prob += delta;
 384
 385         if (delta > 0) {
 386                 /* prevent overflow */
 387                 if (q->vars.prob < oldprob) {
 388                         q->vars.prob = MAX_PROB;
 389                         /* Prevent normalization error. If probability is at
 390                          * maximum value already, we normalize it here, and
 391                          * skip the check to do a non-linear drop in the next
 392                          * section.
 393                          */
 394                         update_prob = false;
 395                 }
 396         } else {
 397                 /* prevent underflow */
 398                 if (q->vars.prob > oldprob)
 399                         q->vars.prob = 0;
 400         }
 401
 402         /* Non-linear drop in probability: Reduce drop probability quickly if
 403          * delay is 0 for 2 consecutive Tupdate periods.
 404          */
 405
 406         if ((qdelay == 0) && (qdelay_old == 0) && update_prob)
 407                 q->vars.prob = (q->vars.prob * 98) / 100;
 408
 409         q->vars.qdelay = qdelay;
 410         q->vars.qlen_old = qlen;
 411
 412         /* We restart the measurement cycle if the following conditions are met
 413          * 1. If the delay has been low for 2 consecutive Tupdate periods
 414          * 2. Calculated drop probability is zero
 415          * 3. We have atleast one estimate for the avg_dq_rate ie.,
 416          *    is a non-zero value
 417          */
 418         if ((q->vars.qdelay < q->params.target / 2) &&
 419             (q->vars.qdelay_old < q->params.target / 2) &&
 420             (q->vars.prob == 0) &&
 421             (q->vars.avg_dq_rate > 0))
 422                 pie_vars_init(&q->vars);
 423 }
 424
 425 static void pie_timer(unsigned long arg)
 426 {
 427         struct Qdisc *sch = (struct Qdisc *)arg;
 428         struct pie_sched_data *q = qdisc_priv(sch);
 429         spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch));
 430
 431         spin_lock(root_lock);
 432         calculate_probability(sch);
 433
 434         /* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */
 435         if (q->params.tupdate)
 436                 mod_timer(&q->adapt_timer, jiffies + q->params.tupdate);
 437         spin_unlock(root_lock);
 438
 439 }
 440
 441 static int pie_init(struct Qdisc *sch, struct nlattr *opt)
 442 {
 443         struct pie_sched_data *q = qdisc_priv(sch);
 444
 445         pie_params_init(&q->params);
 446         pie_vars_init(&q->vars);
 447         sch->limit = q->params.limit;
 448
 449         setup_timer(&q->adapt_timer, pie_timer, (unsigned long)sch);
 450
 451         if (opt) {
 452                 int err = pie_change(sch, opt);
 453
 454                 if (err)
 455                         return err;
 456         }
 457
 458         mod_timer(&q->adapt_timer, jiffies + HZ / 2);
 459         return 0;
 460 }
 461
 462 static int pie_dump(struct Qdisc *sch, struct sk_buff *skb)
 463 {
 464         struct pie_sched_data *q = qdisc_priv(sch);
 465         struct nlattr *opts;
 466
 467         opts = nla_nest_start(skb, TCA_OPTIONS);
 468         if (opts == NULL)
 469                 goto nla_put_failure;
 470
 471         /* convert target from pschedtime to us */
 472         if (nla_put_u32(skb, TCA_PIE_TARGET,
 473                         ((u32) PSCHED_TICKS2NS(q->params.target)) /
 474                         NSEC_PER_USEC) ||
 475             nla_put_u32(skb, TCA_PIE_LIMIT, sch->limit) ||
 476             nla_put_u32(skb, TCA_PIE_TUPDATE, jiffies_to_usecs(q->params.tupdate)) ||
 477             nla_put_u32(skb, TCA_PIE_ALPHA, q->params.alpha) ||
 478             nla_put_u32(skb, TCA_PIE_BETA, q->params.beta) ||
 479             nla_put_u32(skb, TCA_PIE_ECN, q->params.ecn) ||
 480             nla_put_u32(skb, TCA_PIE_BYTEMODE, q->params.bytemode))
 481                 goto nla_put_failure;
 482
 483         return nla_nest_end(skb, opts);
 484
 485 nla_put_failure:
 486         nla_nest_cancel(skb, opts);
 487         return -1;
 488
 489 }
 490
 491 static int pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 492 {
 493         struct pie_sched_data *q = qdisc_priv(sch);
 494         struct tc_pie_xstats st = {
 495                 .prob           = q->vars.prob,
 496                 .delay          = ((u32) PSCHED_TICKS2NS(q->vars.qdelay)) /
 497                                    NSEC_PER_USEC,
 498                 /* unscale and return dq_rate in bytes per sec */
 499                 .avg_dq_rate    = q->vars.avg_dq_rate *
 500                                   (PSCHED_TICKS_PER_SEC) >> PIE_SCALE,
 501                 .packets_in     = q->stats.packets_in,
 502                 .overlimit      = q->stats.overlimit,
 503                 .maxq           = q->stats.maxq,
 504                 .dropped        = q->stats.dropped,
 505                 .ecn_mark       = q->stats.ecn_mark,
 506         };
 507
 508         return gnet_stats_copy_app(d, &st, sizeof(st));
 509 }
 510
 511 static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch)
 512 {
 513         struct sk_buff *skb;
 514         skb = qdisc_dequeue_head(sch);
 515
 516         if (!skb)
 517                 return NULL;
 518
 519         pie_process_dequeue(sch, skb);
 520         return skb;
 521 }
 522
 523 static void pie_reset(struct Qdisc *sch)
 524 {
 525         struct pie_sched_data *q = qdisc_priv(sch);
 526         qdisc_reset_queue(sch);
 527         pie_vars_init(&q->vars);
 528 }
 529
 530 static void pie_destroy(struct Qdisc *sch)
 531 {
 532         struct pie_sched_data *q = qdisc_priv(sch);
 533         q->params.tupdate = 0;
 534         del_timer_sync(&q->adapt_timer);
 535 }
 536
 537 static struct Qdisc_ops pie_qdisc_ops __read_mostly = {
 538         .id = "pie",
 539         .priv_size      = sizeof(struct pie_sched_data),
 540         .enqueue        = pie_qdisc_enqueue,
 541         .dequeue        = pie_qdisc_dequeue,
 542         .peek           = qdisc_peek_dequeued,
 543         .init           = pie_init,
 544         .destroy        = pie_destroy,
 545         .reset          = pie_reset,
 546         .change         = pie_change,
 547         .dump           = pie_dump,
 548         .dump_stats     = pie_dump_stats,
 549         .owner          = THIS_MODULE,
 550 };
 551
 552 static int __init pie_module_init(void)
 553 {
 554         return register_qdisc(&pie_qdisc_ops);
 555 }
 556
 557 static void __exit pie_module_exit(void)
 558 {
 559         unregister_qdisc(&pie_qdisc_ops);
 560 }
 561
 562 module_init(pie_module_init);
 563 module_exit(pie_module_exit);
 564
 565 MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler");
 566 MODULE_AUTHOR("Vijay Subramanian");
 567 MODULE_AUTHOR("Mythili Prabhu");
 568 MODULE_LICENSE("GPL");