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         struct Qdisc *sch;
  78 };
  79
  80 static void pie_params_init(struct pie_params *params)
  81 {
  82         params->alpha = 2;
  83         params->beta = 20;
  84         params->tupdate = usecs_to_jiffies(30 * USEC_PER_MSEC); /* 30 ms */
  85         params->limit = 1000;   /* default of 1000 packets */
  86         params->target = PSCHED_NS2TICKS(20 * NSEC_PER_MSEC);   /* 20 ms */
  87         params->ecn = false;
  88         params->bytemode = false;
  89 }
  90
  91 static void pie_vars_init(struct pie_vars *vars)
  92 {
  93         vars->dq_count = DQCOUNT_INVALID;
  94         vars->avg_dq_rate = 0;
  95         /* default of 100 ms in pschedtime */
  96         vars->burst_time = PSCHED_NS2TICKS(100 * NSEC_PER_MSEC);
  97 }
  98
  99 static bool drop_early(struct Qdisc *sch, u32 packet_size)
 100 {
 101         struct pie_sched_data *q = qdisc_priv(sch);
 102         u32 rnd;
 103         u32 local_prob = q->vars.prob;
 104         u32 mtu = psched_mtu(qdisc_dev(sch));
 105
 106         /* If there is still burst allowance left skip random early drop */
 107         if (q->vars.burst_time > 0)
 108                 return false;
 109
 110         /* If current delay is less than half of target, and
 111          * if drop prob is low already, disable early_drop
 112          */
 113         if ((q->vars.qdelay < q->params.target / 2)
 114             && (q->vars.prob < MAX_PROB / 5))
 115                 return false;
 116
 117         /* If we have fewer than 2 mtu-sized packets, disable drop_early,
 118          * similar to min_th in RED
 119          */
 120         if (sch->qstats.backlog < 2 * mtu)
 121                 return false;
 122
 123         /* If bytemode is turned on, use packet size to compute new
 124          * probablity. Smaller packets will have lower drop prob in this case
 125          */
 126         if (q->params.bytemode && packet_size <= mtu)
 127                 local_prob = (local_prob / mtu) * packet_size;
 128         else
 129                 local_prob = q->vars.prob;
 130
 131         rnd = prandom_u32();
 132         if (rnd < local_prob)
 133                 return true;
 134
 135         return false;
 136 }
 137
 138 static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 139                              struct sk_buff **to_free)
 140 {
 141         struct pie_sched_data *q = qdisc_priv(sch);
 142         bool enqueue = false;
 143
 144         if (unlikely(qdisc_qlen(sch) >= sch->limit)) {
 145                 q->stats.overlimit++;
 146                 goto out;
 147         }
 148
 149         if (!drop_early(sch, skb->len)) {
 150                 enqueue = true;
 151         } else if (q->params.ecn && (q->vars.prob <= MAX_PROB / 10) &&
 152                    INET_ECN_set_ce(skb)) {
 153                 /* If packet is ecn capable, mark it if drop probability
 154                  * is lower than 10%, else drop it.
 155                  */
 156                 q->stats.ecn_mark++;
 157                 enqueue = true;
 158         }
 159
 160         /* we can enqueue the packet */
 161         if (enqueue) {
 162                 q->stats.packets_in++;
 163                 if (qdisc_qlen(sch) > q->stats.maxq)
 164                         q->stats.maxq = qdisc_qlen(sch);
 165
 166                 return qdisc_enqueue_tail(skb, sch);
 167         }
 168
 169 out:
 170         q->stats.dropped++;
 171         return qdisc_drop(skb, sch, to_free);
 172 }
 173
 174 static const struct nla_policy pie_policy[TCA_PIE_MAX + 1] = {
 175         [TCA_PIE_TARGET] = {.type = NLA_U32},
 176         [TCA_PIE_LIMIT] = {.type = NLA_U32},
 177         [TCA_PIE_TUPDATE] = {.type = NLA_U32},
 178         [TCA_PIE_ALPHA] = {.type = NLA_U32},
 179         [TCA_PIE_BETA] = {.type = NLA_U32},
 180         [TCA_PIE_ECN] = {.type = NLA_U32},
 181         [TCA_PIE_BYTEMODE] = {.type = NLA_U32},
 182 };
 183
 184 static int pie_change(struct Qdisc *sch, struct nlattr *opt,
 185                       struct netlink_ext_ack *extack)
 186 {
 187         struct pie_sched_data *q = qdisc_priv(sch);
 188         struct nlattr *tb[TCA_PIE_MAX + 1];
 189         unsigned int qlen, dropped = 0;
 190         int err;
 191
 192         if (!opt)
 193                 return -EINVAL;
 194
 195         err = nla_parse_nested(tb, TCA_PIE_MAX, opt, pie_policy, NULL);
 196         if (err < 0)
 197                 return err;
 198
 199         sch_tree_lock(sch);
 200
 201         /* convert from microseconds to pschedtime */
 202         if (tb[TCA_PIE_TARGET]) {
 203                 /* target is in us */
 204                 u32 target = nla_get_u32(tb[TCA_PIE_TARGET]);
 205
 206                 /* convert to pschedtime */
 207                 q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC);
 208         }
 209
 210         /* tupdate is in jiffies */
 211         if (tb[TCA_PIE_TUPDATE])
 212                 q->params.tupdate = usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE]));
 213
 214         if (tb[TCA_PIE_LIMIT]) {
 215                 u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]);
 216
 217                 q->params.limit = limit;
 218                 sch->limit = limit;
 219         }
 220
 221         if (tb[TCA_PIE_ALPHA])
 222                 q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]);
 223
 224         if (tb[TCA_PIE_BETA])
 225                 q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]);
 226
 227         if (tb[TCA_PIE_ECN])
 228                 q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]);
 229
 230         if (tb[TCA_PIE_BYTEMODE])
 231                 q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]);
 232
 233         /* Drop excess packets if new limit is lower */
 234         qlen = sch->q.qlen;
 235         while (sch->q.qlen > sch->limit) {
 236                 struct sk_buff *skb = __qdisc_dequeue_head(&sch->q);
 237
 238                 dropped += qdisc_pkt_len(skb);
 239                 qdisc_qstats_backlog_dec(sch, skb);
 240                 rtnl_qdisc_drop(skb, sch);
 241         }
 242         qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped);
 243
 244         sch_tree_unlock(sch);
 245         return 0;
 246 }
 247
 248 static void pie_process_dequeue(struct Qdisc *sch, struct sk_buff *skb)
 249 {
 250
 251         struct pie_sched_data *q = qdisc_priv(sch);
 252         int qlen = sch->qstats.backlog; /* current queue size in bytes */
 253
 254         /* If current queue is about 10 packets or more and dq_count is unset
 255          * we have enough packets to calculate the drain rate. Save
 256          * current time as dq_tstamp and start measurement cycle.
 257          */
 258         if (qlen >= QUEUE_THRESHOLD && q->vars.dq_count == DQCOUNT_INVALID) {
 259                 q->vars.dq_tstamp = psched_get_time();
 260                 q->vars.dq_count = 0;
 261         }
 262
 263         /* Calculate the average drain rate from this value.  If queue length
 264          * has receded to a small value viz., <= QUEUE_THRESHOLD bytes,reset
 265          * the dq_count to -1 as we don't have enough packets to calculate the
 266          * drain rate anymore The following if block is entered only when we
 267          * have a substantial queue built up (QUEUE_THRESHOLD bytes or more)
 268          * and we calculate the drain rate for the threshold here.  dq_count is
 269          * in bytes, time difference in psched_time, hence rate is in
 270          * bytes/psched_time.
 271          */
 272         if (q->vars.dq_count != DQCOUNT_INVALID) {
 273                 q->vars.dq_count += skb->len;
 274
 275                 if (q->vars.dq_count >= QUEUE_THRESHOLD) {
 276                         psched_time_t now = psched_get_time();
 277                         u32 dtime = now - q->vars.dq_tstamp;
 278                         u32 count = q->vars.dq_count << PIE_SCALE;
 279
 280                         if (dtime == 0)
 281                                 return;
 282
 283                         count = count / dtime;
 284
 285                         if (q->vars.avg_dq_rate == 0)
 286                                 q->vars.avg_dq_rate = count;
 287                         else
 288                                 q->vars.avg_dq_rate =
 289                                     (q->vars.avg_dq_rate -
 290                                      (q->vars.avg_dq_rate >> 3)) + (count >> 3);
 291
 292                         /* If the queue has receded below the threshold, we hold
 293                          * on to the last drain rate calculated, else we reset
 294                          * dq_count to 0 to re-enter the if block when the next
 295                          * packet is dequeued
 296                          */
 297                         if (qlen < QUEUE_THRESHOLD)
 298                                 q->vars.dq_count = DQCOUNT_INVALID;
 299                         else {
 300                                 q->vars.dq_count = 0;
 301                                 q->vars.dq_tstamp = psched_get_time();
 302                         }
 303
 304                         if (q->vars.burst_time > 0) {
 305                                 if (q->vars.burst_time > dtime)
 306                                         q->vars.burst_time -= dtime;
 307                                 else
 308                                         q->vars.burst_time = 0;
 309                         }
 310                 }
 311         }
 312 }
 313
 314 static void calculate_probability(struct Qdisc *sch)
 315 {
 316         struct pie_sched_data *q = qdisc_priv(sch);
 317         u32 qlen = sch->qstats.backlog; /* queue size in bytes */
 318         psched_time_t qdelay = 0;       /* in pschedtime */
 319         psched_time_t qdelay_old = q->vars.qdelay;      /* in pschedtime */
 320         s32 delta = 0;          /* determines the change in probability */
 321         u32 oldprob;
 322         u32 alpha, beta;
 323         bool update_prob = true;
 324
 325         q->vars.qdelay_old = q->vars.qdelay;
 326
 327         if (q->vars.avg_dq_rate > 0)
 328                 qdelay = (qlen << PIE_SCALE) / q->vars.avg_dq_rate;
 329         else
 330                 qdelay = 0;
 331
 332         /* If qdelay is zero and qlen is not, it means qlen is very small, less
 333          * than dequeue_rate, so we do not update probabilty in this round
 334          */
 335         if (qdelay == 0 && qlen != 0)
 336                 update_prob = false;
 337
 338         /* In the algorithm, alpha and beta are between 0 and 2 with typical
 339          * value for alpha as 0.125. In this implementation, we use values 0-32
 340          * passed from user space to represent this. Also, alpha and beta have
 341          * unit of HZ and need to be scaled before they can used to update
 342          * probability. alpha/beta are updated locally below by 1) scaling them
 343          * appropriately 2) scaling down by 16 to come to 0-2 range.
 344          * Please see paper for details.
 345          *
 346          * We scale alpha and beta differently depending on whether we are in
 347          * light, medium or high dropping mode.
 348          */
 349         if (q->vars.prob < MAX_PROB / 100) {
 350                 alpha =
 351                     (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
 352                 beta =
 353                     (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
 354         } else if (q->vars.prob < MAX_PROB / 10) {
 355                 alpha =
 356                     (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
 357                 beta =
 358                     (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
 359         } else {
 360                 alpha =
 361                     (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
 362                 beta =
 363                     (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
 364         }
 365
 366         /* alpha and beta should be between 0 and 32, in multiples of 1/16 */
 367         delta += alpha * ((qdelay - q->params.target));
 368         delta += beta * ((qdelay - qdelay_old));
 369
 370         oldprob = q->vars.prob;
 371
 372         /* to ensure we increase probability in steps of no more than 2% */
 373         if (delta > (s32) (MAX_PROB / (100 / 2)) &&
 374             q->vars.prob >= MAX_PROB / 10)
 375                 delta = (MAX_PROB / 100) * 2;
 376
 377         /* Non-linear drop:
 378          * Tune drop probability to increase quickly for high delays(>= 250ms)
 379          * 250ms is derived through experiments and provides error protection
 380          */
 381
 382         if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC)))
 383                 delta += MAX_PROB / (100 / 2);
 384
 385         q->vars.prob += delta;
 386
 387         if (delta > 0) {
 388                 /* prevent overflow */
 389                 if (q->vars.prob < oldprob) {
 390                         q->vars.prob = MAX_PROB;
 391                         /* Prevent normalization error. If probability is at
 392                          * maximum value already, we normalize it here, and
 393                          * skip the check to do a non-linear drop in the next
 394                          * section.
 395                          */
 396                         update_prob = false;
 397                 }
 398         } else {
 399                 /* prevent underflow */
 400                 if (q->vars.prob > oldprob)
 401                         q->vars.prob = 0;
 402         }
 403
 404         /* Non-linear drop in probability: Reduce drop probability quickly if
 405          * delay is 0 for 2 consecutive Tupdate periods.
 406          */
 407
 408         if ((qdelay == 0) && (qdelay_old == 0) && update_prob)
 409                 q->vars.prob = (q->vars.prob * 98) / 100;
 410
 411         q->vars.qdelay = qdelay;
 412         q->vars.qlen_old = qlen;
 413
 414         /* We restart the measurement cycle if the following conditions are met
 415          * 1. If the delay has been low for 2 consecutive Tupdate periods
 416          * 2. Calculated drop probability is zero
 417          * 3. We have atleast one estimate for the avg_dq_rate ie.,
 418          *    is a non-zero value
 419          */
 420         if ((q->vars.qdelay < q->params.target / 2) &&
 421             (q->vars.qdelay_old < q->params.target / 2) &&
 422             (q->vars.prob == 0) &&
 423             (q->vars.avg_dq_rate > 0))
 424                 pie_vars_init(&q->vars);
 425 }
 426
 427 static void pie_timer(struct timer_list *t)
 428 {
 429         struct pie_sched_data *q = from_timer(q, t, adapt_timer);
 430         struct Qdisc *sch = q->sch;
 431         spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch));
 432
 433         spin_lock(root_lock);
 434         calculate_probability(sch);
 435
 436         /* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */
 437         if (q->params.tupdate)
 438                 mod_timer(&q->adapt_timer, jiffies + q->params.tupdate);
 439         spin_unlock(root_lock);
 440
 441 }
 442
 443 static int pie_init(struct Qdisc *sch, struct nlattr *opt,
 444                     struct netlink_ext_ack *extack)
 445 {
 446         struct pie_sched_data *q = qdisc_priv(sch);
 447
 448         pie_params_init(&q->params);
 449         pie_vars_init(&q->vars);
 450         sch->limit = q->params.limit;
 451
 452         q->sch = sch;
 453         timer_setup(&q->adapt_timer, pie_timer, 0);
 454
 455         if (opt) {
 456                 int err = pie_change(sch, opt, extack);
 457
 458                 if (err)
 459                         return err;
 460         }
 461
 462         mod_timer(&q->adapt_timer, jiffies + HZ / 2);
 463         return 0;
 464 }
 465
 466 static int pie_dump(struct Qdisc *sch, struct sk_buff *skb)
 467 {
 468         struct pie_sched_data *q = qdisc_priv(sch);
 469         struct nlattr *opts;
 470
 471         opts = nla_nest_start(skb, TCA_OPTIONS);
 472         if (opts == NULL)
 473                 goto nla_put_failure;
 474
 475         /* convert target from pschedtime to us */
 476         if (nla_put_u32(skb, TCA_PIE_TARGET,
 477                         ((u32) PSCHED_TICKS2NS(q->params.target)) /
 478                         NSEC_PER_USEC) ||
 479             nla_put_u32(skb, TCA_PIE_LIMIT, sch->limit) ||
 480             nla_put_u32(skb, TCA_PIE_TUPDATE, jiffies_to_usecs(q->params.tupdate)) ||
 481             nla_put_u32(skb, TCA_PIE_ALPHA, q->params.alpha) ||
 482             nla_put_u32(skb, TCA_PIE_BETA, q->params.beta) ||
 483             nla_put_u32(skb, TCA_PIE_ECN, q->params.ecn) ||
 484             nla_put_u32(skb, TCA_PIE_BYTEMODE, q->params.bytemode))
 485                 goto nla_put_failure;
 486
 487         return nla_nest_end(skb, opts);
 488
 489 nla_put_failure:
 490         nla_nest_cancel(skb, opts);
 491         return -1;
 492
 493 }
 494
 495 static int pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 496 {
 497         struct pie_sched_data *q = qdisc_priv(sch);
 498         struct tc_pie_xstats st = {
 499                 .prob           = q->vars.prob,
 500                 .delay          = ((u32) PSCHED_TICKS2NS(q->vars.qdelay)) /
 501                                    NSEC_PER_USEC,
 502                 /* unscale and return dq_rate in bytes per sec */
 503                 .avg_dq_rate    = q->vars.avg_dq_rate *
 504                                   (PSCHED_TICKS_PER_SEC) >> PIE_SCALE,
 505                 .packets_in     = q->stats.packets_in,
 506                 .overlimit      = q->stats.overlimit,
 507                 .maxq           = q->stats.maxq,
 508                 .dropped        = q->stats.dropped,
 509                 .ecn_mark       = q->stats.ecn_mark,
 510         };
 511
 512         return gnet_stats_copy_app(d, &st, sizeof(st));
 513 }
 514
 515 static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch)
 516 {
 517         struct sk_buff *skb;
 518         skb = qdisc_dequeue_head(sch);
 519
 520         if (!skb)
 521                 return NULL;
 522
 523         pie_process_dequeue(sch, skb);
 524         return skb;
 525 }
 526
 527 static void pie_reset(struct Qdisc *sch)
 528 {
 529         struct pie_sched_data *q = qdisc_priv(sch);
 530         qdisc_reset_queue(sch);
 531         pie_vars_init(&q->vars);
 532 }
 533
 534 static void pie_destroy(struct Qdisc *sch)
 535 {
 536         struct pie_sched_data *q = qdisc_priv(sch);
 537         q->params.tupdate = 0;
 538         del_timer_sync(&q->adapt_timer);
 539 }
 540
 541 static struct Qdisc_ops pie_qdisc_ops __read_mostly = {
 542         .id = "pie",
 543         .priv_size      = sizeof(struct pie_sched_data),
 544         .enqueue        = pie_qdisc_enqueue,
 545         .dequeue        = pie_qdisc_dequeue,
 546         .peek           = qdisc_peek_dequeued,
 547         .init           = pie_init,
 548         .destroy        = pie_destroy,
 549         .reset          = pie_reset,
 550         .change         = pie_change,
 551         .dump           = pie_dump,
 552         .dump_stats     = pie_dump_stats,
 553         .owner          = THIS_MODULE,
 554 };
 555
 556 static int __init pie_module_init(void)
 557 {
 558         return register_qdisc(&pie_qdisc_ops);
 559 }
 560
 561 static void __exit pie_module_exit(void)
 562 {
 563         unregister_qdisc(&pie_qdisc_ops);
 564 }
 565
 566 module_init(pie_module_init);
 567 module_exit(pie_module_exit);
 568
 569 MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler");
 570 MODULE_AUTHOR("Vijay Subramanian");
 571 MODULE_AUTHOR("Mythili Prabhu");
 572 MODULE_LICENSE("GPL");