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"); 573