1 // SPDX-License-Identifier: GPL-2.0-only 2 /* Copyright (C) 2013 Cisco Systems, Inc, 2013. 3 * 4 * Author: Vijay Subramanian <vijaynsu@cisco.com> 5 * Author: Mythili Prabhu <mysuryan@cisco.com> 6 * 7 * ECN support is added by Naeem Khademi <naeemk@ifi.uio.no> 8 * University of Oslo, Norway. 9 * 10 * References: 11 * RFC 8033: https://tools.ietf.org/html/rfc8033 12 */ 13 14 #include <linux/module.h> 15 #include <linux/slab.h> 16 #include <linux/types.h> 17 #include <linux/kernel.h> 18 #include <linux/errno.h> 19 #include <linux/skbuff.h> 20 #include <net/pkt_sched.h> 21 #include <net/inet_ecn.h> 22 #include <net/pie.h> 23 24 /* private data for the Qdisc */ 25 struct pie_sched_data { 26 struct pie_vars vars; 27 struct pie_params params; 28 struct pie_stats stats; 29 struct timer_list adapt_timer; 30 struct Qdisc *sch; 31 }; 32 33 bool pie_drop_early(struct Qdisc *sch, struct pie_params *params, 34 struct pie_vars *vars, u32 backlog, u32 packet_size) 35 { 36 u64 rnd; 37 u64 local_prob = vars->prob; 38 u32 mtu = psched_mtu(qdisc_dev(sch)); 39 40 /* If there is still burst allowance left skip random early drop */ 41 if (vars->burst_time > 0) 42 return false; 43 44 /* If current delay is less than half of target, and 45 * if drop prob is low already, disable early_drop 46 */ 47 if ((vars->qdelay < params->target / 2) && 48 (vars->prob < MAX_PROB / 5)) 49 return false; 50 51 /* If we have fewer than 2 mtu-sized packets, disable pie_drop_early, 52 * similar to min_th in RED 53 */ 54 if (backlog < 2 * mtu) 55 return false; 56 57 /* If bytemode is turned on, use packet size to compute new 58 * probablity. Smaller packets will have lower drop prob in this case 59 */ 60 if (params->bytemode && packet_size <= mtu) 61 local_prob = (u64)packet_size * div_u64(local_prob, mtu); 62 else 63 local_prob = vars->prob; 64 65 if (local_prob == 0) 66 vars->accu_prob = 0; 67 else 68 vars->accu_prob += local_prob; 69 70 if (vars->accu_prob < (MAX_PROB / 100) * 85) 71 return false; 72 if (vars->accu_prob >= (MAX_PROB / 2) * 17) 73 return true; 74 75 prandom_bytes(&rnd, 8); 76 if ((rnd >> BITS_PER_BYTE) < local_prob) { 77 vars->accu_prob = 0; 78 return true; 79 } 80 81 return false; 82 } 83 EXPORT_SYMBOL_GPL(pie_drop_early); 84 85 static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch, 86 struct sk_buff **to_free) 87 { 88 struct pie_sched_data *q = qdisc_priv(sch); 89 bool enqueue = false; 90 91 if (unlikely(qdisc_qlen(sch) >= sch->limit)) { 92 q->stats.overlimit++; 93 goto out; 94 } 95 96 if (!pie_drop_early(sch, &q->params, &q->vars, sch->qstats.backlog, 97 skb->len)) { 98 enqueue = true; 99 } else if (q->params.ecn && (q->vars.prob <= MAX_PROB / 10) && 100 INET_ECN_set_ce(skb)) { 101 /* If packet is ecn capable, mark it if drop probability 102 * is lower than 10%, else drop it. 103 */ 104 q->stats.ecn_mark++; 105 enqueue = true; 106 } 107 108 /* we can enqueue the packet */ 109 if (enqueue) { 110 /* Set enqueue time only when dq_rate_estimator is disabled. */ 111 if (!q->params.dq_rate_estimator) 112 pie_set_enqueue_time(skb); 113 114 q->stats.packets_in++; 115 if (qdisc_qlen(sch) > q->stats.maxq) 116 q->stats.maxq = qdisc_qlen(sch); 117 118 return qdisc_enqueue_tail(skb, sch); 119 } 120 121 out: 122 q->stats.dropped++; 123 q->vars.accu_prob = 0; 124 return qdisc_drop(skb, sch, to_free); 125 } 126 127 static const struct nla_policy pie_policy[TCA_PIE_MAX + 1] = { 128 [TCA_PIE_TARGET] = {.type = NLA_U32}, 129 [TCA_PIE_LIMIT] = {.type = NLA_U32}, 130 [TCA_PIE_TUPDATE] = {.type = NLA_U32}, 131 [TCA_PIE_ALPHA] = {.type = NLA_U32}, 132 [TCA_PIE_BETA] = {.type = NLA_U32}, 133 [TCA_PIE_ECN] = {.type = NLA_U32}, 134 [TCA_PIE_BYTEMODE] = {.type = NLA_U32}, 135 [TCA_PIE_DQ_RATE_ESTIMATOR] = {.type = NLA_U32}, 136 }; 137 138 static int pie_change(struct Qdisc *sch, struct nlattr *opt, 139 struct netlink_ext_ack *extack) 140 { 141 struct pie_sched_data *q = qdisc_priv(sch); 142 struct nlattr *tb[TCA_PIE_MAX + 1]; 143 unsigned int qlen, dropped = 0; 144 int err; 145 146 if (!opt) 147 return -EINVAL; 148 149 err = nla_parse_nested_deprecated(tb, TCA_PIE_MAX, opt, pie_policy, 150 NULL); 151 if (err < 0) 152 return err; 153 154 sch_tree_lock(sch); 155 156 /* convert from microseconds to pschedtime */ 157 if (tb[TCA_PIE_TARGET]) { 158 /* target is in us */ 159 u32 target = nla_get_u32(tb[TCA_PIE_TARGET]); 160 161 /* convert to pschedtime */ 162 q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC); 163 } 164 165 /* tupdate is in jiffies */ 166 if (tb[TCA_PIE_TUPDATE]) 167 q->params.tupdate = 168 usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE])); 169 170 if (tb[TCA_PIE_LIMIT]) { 171 u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]); 172 173 q->params.limit = limit; 174 sch->limit = limit; 175 } 176 177 if (tb[TCA_PIE_ALPHA]) 178 q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]); 179 180 if (tb[TCA_PIE_BETA]) 181 q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]); 182 183 if (tb[TCA_PIE_ECN]) 184 q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]); 185 186 if (tb[TCA_PIE_BYTEMODE]) 187 q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]); 188 189 if (tb[TCA_PIE_DQ_RATE_ESTIMATOR]) 190 q->params.dq_rate_estimator = 191 nla_get_u32(tb[TCA_PIE_DQ_RATE_ESTIMATOR]); 192 193 /* Drop excess packets if new limit is lower */ 194 qlen = sch->q.qlen; 195 while (sch->q.qlen > sch->limit) { 196 struct sk_buff *skb = __qdisc_dequeue_head(&sch->q); 197 198 dropped += qdisc_pkt_len(skb); 199 qdisc_qstats_backlog_dec(sch, skb); 200 rtnl_qdisc_drop(skb, sch); 201 } 202 qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped); 203 204 sch_tree_unlock(sch); 205 return 0; 206 } 207 208 void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params, 209 struct pie_vars *vars, u32 backlog) 210 { 211 psched_time_t now = psched_get_time(); 212 u32 dtime = 0; 213 214 /* If dq_rate_estimator is disabled, calculate qdelay using the 215 * packet timestamp. 216 */ 217 if (!params->dq_rate_estimator) { 218 vars->qdelay = now - pie_get_enqueue_time(skb); 219 220 if (vars->dq_tstamp != DTIME_INVALID) 221 dtime = now - vars->dq_tstamp; 222 223 vars->dq_tstamp = now; 224 225 if (backlog == 0) 226 vars->qdelay = 0; 227 228 if (dtime == 0) 229 return; 230 231 goto burst_allowance_reduction; 232 } 233 234 /* If current queue is about 10 packets or more and dq_count is unset 235 * we have enough packets to calculate the drain rate. Save 236 * current time as dq_tstamp and start measurement cycle. 237 */ 238 if (backlog >= QUEUE_THRESHOLD && vars->dq_count == DQCOUNT_INVALID) { 239 vars->dq_tstamp = psched_get_time(); 240 vars->dq_count = 0; 241 } 242 243 /* Calculate the average drain rate from this value. If queue length 244 * has receded to a small value viz., <= QUEUE_THRESHOLD bytes, reset 245 * the dq_count to -1 as we don't have enough packets to calculate the 246 * drain rate anymore. The following if block is entered only when we 247 * have a substantial queue built up (QUEUE_THRESHOLD bytes or more) 248 * and we calculate the drain rate for the threshold here. dq_count is 249 * in bytes, time difference in psched_time, hence rate is in 250 * bytes/psched_time. 251 */ 252 if (vars->dq_count != DQCOUNT_INVALID) { 253 vars->dq_count += skb->len; 254 255 if (vars->dq_count >= QUEUE_THRESHOLD) { 256 u32 count = vars->dq_count << PIE_SCALE; 257 258 dtime = now - vars->dq_tstamp; 259 260 if (dtime == 0) 261 return; 262 263 count = count / dtime; 264 265 if (vars->avg_dq_rate == 0) 266 vars->avg_dq_rate = count; 267 else 268 vars->avg_dq_rate = 269 (vars->avg_dq_rate - 270 (vars->avg_dq_rate >> 3)) + (count >> 3); 271 272 /* If the queue has receded below the threshold, we hold 273 * on to the last drain rate calculated, else we reset 274 * dq_count to 0 to re-enter the if block when the next 275 * packet is dequeued 276 */ 277 if (backlog < QUEUE_THRESHOLD) { 278 vars->dq_count = DQCOUNT_INVALID; 279 } else { 280 vars->dq_count = 0; 281 vars->dq_tstamp = psched_get_time(); 282 } 283 284 goto burst_allowance_reduction; 285 } 286 } 287 288 return; 289 290 burst_allowance_reduction: 291 if (vars->burst_time > 0) { 292 if (vars->burst_time > dtime) 293 vars->burst_time -= dtime; 294 else 295 vars->burst_time = 0; 296 } 297 } 298 EXPORT_SYMBOL_GPL(pie_process_dequeue); 299 300 void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars, 301 u32 backlog) 302 { 303 psched_time_t qdelay = 0; /* in pschedtime */ 304 psched_time_t qdelay_old = 0; /* in pschedtime */ 305 s64 delta = 0; /* determines the change in probability */ 306 u64 oldprob; 307 u64 alpha, beta; 308 u32 power; 309 bool update_prob = true; 310 311 if (params->dq_rate_estimator) { 312 qdelay_old = vars->qdelay; 313 vars->qdelay_old = vars->qdelay; 314 315 if (vars->avg_dq_rate > 0) 316 qdelay = (backlog << PIE_SCALE) / vars->avg_dq_rate; 317 else 318 qdelay = 0; 319 } else { 320 qdelay = vars->qdelay; 321 qdelay_old = vars->qdelay_old; 322 } 323 324 /* If qdelay is zero and backlog is not, it means backlog is very small, 325 * so we do not update probabilty in this round. 326 */ 327 if (qdelay == 0 && backlog != 0) 328 update_prob = false; 329 330 /* In the algorithm, alpha and beta are between 0 and 2 with typical 331 * value for alpha as 0.125. In this implementation, we use values 0-32 332 * passed from user space to represent this. Also, alpha and beta have 333 * unit of HZ and need to be scaled before they can used to update 334 * probability. alpha/beta are updated locally below by scaling down 335 * by 16 to come to 0-2 range. 336 */ 337 alpha = ((u64)params->alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4; 338 beta = ((u64)params->beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4; 339 340 /* We scale alpha and beta differently depending on how heavy the 341 * congestion is. Please see RFC 8033 for details. 342 */ 343 if (vars->prob < MAX_PROB / 10) { 344 alpha >>= 1; 345 beta >>= 1; 346 347 power = 100; 348 while (vars->prob < div_u64(MAX_PROB, power) && 349 power <= 1000000) { 350 alpha >>= 2; 351 beta >>= 2; 352 power *= 10; 353 } 354 } 355 356 /* alpha and beta should be between 0 and 32, in multiples of 1/16 */ 357 delta += alpha * (qdelay - params->target); 358 delta += beta * (qdelay - qdelay_old); 359 360 oldprob = vars->prob; 361 362 /* to ensure we increase probability in steps of no more than 2% */ 363 if (delta > (s64)(MAX_PROB / (100 / 2)) && 364 vars->prob >= MAX_PROB / 10) 365 delta = (MAX_PROB / 100) * 2; 366 367 /* Non-linear drop: 368 * Tune drop probability to increase quickly for high delays(>= 250ms) 369 * 250ms is derived through experiments and provides error protection 370 */ 371 372 if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC))) 373 delta += MAX_PROB / (100 / 2); 374 375 vars->prob += delta; 376 377 if (delta > 0) { 378 /* prevent overflow */ 379 if (vars->prob < oldprob) { 380 vars->prob = MAX_PROB; 381 /* Prevent normalization error. If probability is at 382 * maximum value already, we normalize it here, and 383 * skip the check to do a non-linear drop in the next 384 * section. 385 */ 386 update_prob = false; 387 } 388 } else { 389 /* prevent underflow */ 390 if (vars->prob > oldprob) 391 vars->prob = 0; 392 } 393 394 /* Non-linear drop in probability: Reduce drop probability quickly if 395 * delay is 0 for 2 consecutive Tupdate periods. 396 */ 397 398 if (qdelay == 0 && qdelay_old == 0 && update_prob) 399 /* Reduce drop probability to 98.4% */ 400 vars->prob -= vars->prob / 64; 401 402 vars->qdelay = qdelay; 403 vars->backlog_old = backlog; 404 405 /* We restart the measurement cycle if the following conditions are met 406 * 1. If the delay has been low for 2 consecutive Tupdate periods 407 * 2. Calculated drop probability is zero 408 * 3. If average dq_rate_estimator is enabled, we have atleast one 409 * estimate for the avg_dq_rate ie., is a non-zero value 410 */ 411 if ((vars->qdelay < params->target / 2) && 412 (vars->qdelay_old < params->target / 2) && 413 vars->prob == 0 && 414 (!params->dq_rate_estimator || vars->avg_dq_rate > 0)) { 415 pie_vars_init(vars); 416 } 417 418 if (!params->dq_rate_estimator) 419 vars->qdelay_old = qdelay; 420 } 421 EXPORT_SYMBOL_GPL(pie_calculate_probability); 422 423 static void pie_timer(struct timer_list *t) 424 { 425 struct pie_sched_data *q = from_timer(q, t, adapt_timer); 426 struct Qdisc *sch = q->sch; 427 spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch)); 428 429 spin_lock(root_lock); 430 pie_calculate_probability(&q->params, &q->vars, sch->qstats.backlog); 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 static int pie_init(struct Qdisc *sch, struct nlattr *opt, 439 struct netlink_ext_ack *extack) 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 q->sch = sch; 448 timer_setup(&q->adapt_timer, pie_timer, 0); 449 450 if (opt) { 451 int err = pie_change(sch, opt, extack); 452 453 if (err) 454 return err; 455 } 456 457 mod_timer(&q->adapt_timer, jiffies + HZ / 2); 458 return 0; 459 } 460 461 static int pie_dump(struct Qdisc *sch, struct sk_buff *skb) 462 { 463 struct pie_sched_data *q = qdisc_priv(sch); 464 struct nlattr *opts; 465 466 opts = nla_nest_start_noflag(skb, TCA_OPTIONS); 467 if (!opts) 468 goto nla_put_failure; 469 470 /* convert target from pschedtime to us */ 471 if (nla_put_u32(skb, TCA_PIE_TARGET, 472 ((u32)PSCHED_TICKS2NS(q->params.target)) / 473 NSEC_PER_USEC) || 474 nla_put_u32(skb, TCA_PIE_LIMIT, sch->limit) || 475 nla_put_u32(skb, TCA_PIE_TUPDATE, 476 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 nla_put_u32(skb, TCA_PIE_DQ_RATE_ESTIMATOR, 482 q->params.dq_rate_estimator)) 483 goto nla_put_failure; 484 485 return nla_nest_end(skb, opts); 486 487 nla_put_failure: 488 nla_nest_cancel(skb, opts); 489 return -1; 490 } 491 492 static int pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d) 493 { 494 struct pie_sched_data *q = qdisc_priv(sch); 495 struct tc_pie_xstats st = { 496 .prob = q->vars.prob << BITS_PER_BYTE, 497 .delay = ((u32)PSCHED_TICKS2NS(q->vars.qdelay)) / 498 NSEC_PER_USEC, 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 /* avg_dq_rate is only valid if dq_rate_estimator is enabled */ 507 st.dq_rate_estimating = q->params.dq_rate_estimator; 508 509 /* unscale and return dq_rate in bytes per sec */ 510 if (q->params.dq_rate_estimator) 511 st.avg_dq_rate = q->vars.avg_dq_rate * 512 (PSCHED_TICKS_PER_SEC) >> PIE_SCALE; 513 514 return gnet_stats_copy_app(d, &st, sizeof(st)); 515 } 516 517 static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch) 518 { 519 struct pie_sched_data *q = qdisc_priv(sch); 520 struct sk_buff *skb = qdisc_dequeue_head(sch); 521 522 if (!skb) 523 return NULL; 524 525 pie_process_dequeue(skb, &q->params, &q->vars, sch->qstats.backlog); 526 return skb; 527 } 528 529 static void pie_reset(struct Qdisc *sch) 530 { 531 struct pie_sched_data *q = qdisc_priv(sch); 532 533 qdisc_reset_queue(sch); 534 pie_vars_init(&q->vars); 535 } 536 537 static void pie_destroy(struct Qdisc *sch) 538 { 539 struct pie_sched_data *q = qdisc_priv(sch); 540 541 q->params.tupdate = 0; 542 del_timer_sync(&q->adapt_timer); 543 } 544 545 static struct Qdisc_ops pie_qdisc_ops __read_mostly = { 546 .id = "pie", 547 .priv_size = sizeof(struct pie_sched_data), 548 .enqueue = pie_qdisc_enqueue, 549 .dequeue = pie_qdisc_dequeue, 550 .peek = qdisc_peek_dequeued, 551 .init = pie_init, 552 .destroy = pie_destroy, 553 .reset = pie_reset, 554 .change = pie_change, 555 .dump = pie_dump, 556 .dump_stats = pie_dump_stats, 557 .owner = THIS_MODULE, 558 }; 559 560 static int __init pie_module_init(void) 561 { 562 return register_qdisc(&pie_qdisc_ops); 563 } 564 565 static void __exit pie_module_exit(void) 566 { 567 unregister_qdisc(&pie_qdisc_ops); 568 } 569 570 module_init(pie_module_init); 571 module_exit(pie_module_exit); 572 573 MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler"); 574 MODULE_AUTHOR("Vijay Subramanian"); 575 MODULE_AUTHOR("Mythili Prabhu"); 576 MODULE_LICENSE("GPL"); 577