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 */ 40struct 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 */ 51struct 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 */ 63struct 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 */ 72struct 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 79static 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 90static 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 98static 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 137static 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 167out: 168 q->stats.dropped++; 169 return qdisc_drop(skb, sch); 170} 171 172static 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 182static 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 244static 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 310static 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 423static 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 439static 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 460static 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 483nla_put_failure: 484 nla_nest_cancel(skb, opts); 485 return -1; 486 487} 488 489static 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 509static 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 521static 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 528static 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 535static 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 550static int __init pie_module_init(void) 551{ 552 return register_qdisc(&pie_qdisc_ops); 553} 554 555static void __exit pie_module_exit(void) 556{ 557 unregister_qdisc(&pie_qdisc_ops); 558} 559 560module_init(pie_module_init); 561module_exit(pie_module_exit); 562 563MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler"); 564MODULE_AUTHOR("Vijay Subramanian"); 565MODULE_AUTHOR("Mythili Prabhu"); 566MODULE_LICENSE("GPL"); 567