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 get_random_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 err = nla_parse_nested_deprecated(tb, TCA_PIE_MAX, opt, pie_policy, 147 NULL); 148 if (err < 0) 149 return err; 150 151 sch_tree_lock(sch); 152 153 /* convert from microseconds to pschedtime */ 154 if (tb[TCA_PIE_TARGET]) { 155 /* target is in us */ 156 u32 target = nla_get_u32(tb[TCA_PIE_TARGET]); 157 158 /* convert to pschedtime */ 159 q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC); 160 } 161 162 /* tupdate is in jiffies */ 163 if (tb[TCA_PIE_TUPDATE]) 164 q->params.tupdate = 165 usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE])); 166 167 if (tb[TCA_PIE_LIMIT]) { 168 u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]); 169 170 q->params.limit = limit; 171 sch->limit = limit; 172 } 173 174 if (tb[TCA_PIE_ALPHA]) 175 q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]); 176 177 if (tb[TCA_PIE_BETA]) 178 q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]); 179 180 if (tb[TCA_PIE_ECN]) 181 q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]); 182 183 if (tb[TCA_PIE_BYTEMODE]) 184 q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]); 185 186 if (tb[TCA_PIE_DQ_RATE_ESTIMATOR]) 187 q->params.dq_rate_estimator = 188 nla_get_u32(tb[TCA_PIE_DQ_RATE_ESTIMATOR]); 189 190 /* Drop excess packets if new limit is lower */ 191 qlen = sch->q.qlen; 192 while (sch->q.qlen > sch->limit) { 193 struct sk_buff *skb = __qdisc_dequeue_head(&sch->q); 194 195 dropped += qdisc_pkt_len(skb); 196 qdisc_qstats_backlog_dec(sch, skb); 197 rtnl_qdisc_drop(skb, sch); 198 } 199 qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped); 200 201 sch_tree_unlock(sch); 202 return 0; 203 } 204 205 void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params, 206 struct pie_vars *vars, u32 backlog) 207 { 208 psched_time_t now = psched_get_time(); 209 u32 dtime = 0; 210 211 /* If dq_rate_estimator is disabled, calculate qdelay using the 212 * packet timestamp. 213 */ 214 if (!params->dq_rate_estimator) { 215 vars->qdelay = now - pie_get_enqueue_time(skb); 216 217 if (vars->dq_tstamp != DTIME_INVALID) 218 dtime = now - vars->dq_tstamp; 219 220 vars->dq_tstamp = now; 221 222 if (backlog == 0) 223 vars->qdelay = 0; 224 225 if (dtime == 0) 226 return; 227 228 goto burst_allowance_reduction; 229 } 230 231 /* If current queue is about 10 packets or more and dq_count is unset 232 * we have enough packets to calculate the drain rate. Save 233 * current time as dq_tstamp and start measurement cycle. 234 */ 235 if (backlog >= QUEUE_THRESHOLD && vars->dq_count == DQCOUNT_INVALID) { 236 vars->dq_tstamp = psched_get_time(); 237 vars->dq_count = 0; 238 } 239 240 /* Calculate the average drain rate from this value. If queue length 241 * has receded to a small value viz., <= QUEUE_THRESHOLD bytes, reset 242 * the dq_count to -1 as we don't have enough packets to calculate the 243 * drain rate anymore. The following if block is entered only when we 244 * have a substantial queue built up (QUEUE_THRESHOLD bytes or more) 245 * and we calculate the drain rate for the threshold here. dq_count is 246 * in bytes, time difference in psched_time, hence rate is in 247 * bytes/psched_time. 248 */ 249 if (vars->dq_count != DQCOUNT_INVALID) { 250 vars->dq_count += skb->len; 251 252 if (vars->dq_count >= QUEUE_THRESHOLD) { 253 u32 count = vars->dq_count << PIE_SCALE; 254 255 dtime = now - vars->dq_tstamp; 256 257 if (dtime == 0) 258 return; 259 260 count = count / dtime; 261 262 if (vars->avg_dq_rate == 0) 263 vars->avg_dq_rate = count; 264 else 265 vars->avg_dq_rate = 266 (vars->avg_dq_rate - 267 (vars->avg_dq_rate >> 3)) + (count >> 3); 268 269 /* If the queue has receded below the threshold, we hold 270 * on to the last drain rate calculated, else we reset 271 * dq_count to 0 to re-enter the if block when the next 272 * packet is dequeued 273 */ 274 if (backlog < QUEUE_THRESHOLD) { 275 vars->dq_count = DQCOUNT_INVALID; 276 } else { 277 vars->dq_count = 0; 278 vars->dq_tstamp = psched_get_time(); 279 } 280 281 goto burst_allowance_reduction; 282 } 283 } 284 285 return; 286 287 burst_allowance_reduction: 288 if (vars->burst_time > 0) { 289 if (vars->burst_time > dtime) 290 vars->burst_time -= dtime; 291 else 292 vars->burst_time = 0; 293 } 294 } 295 EXPORT_SYMBOL_GPL(pie_process_dequeue); 296 297 void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars, 298 u32 backlog) 299 { 300 psched_time_t qdelay = 0; /* in pschedtime */ 301 psched_time_t qdelay_old = 0; /* in pschedtime */ 302 s64 delta = 0; /* determines the change in probability */ 303 u64 oldprob; 304 u64 alpha, beta; 305 u32 power; 306 bool update_prob = true; 307 308 if (params->dq_rate_estimator) { 309 qdelay_old = vars->qdelay; 310 vars->qdelay_old = vars->qdelay; 311 312 if (vars->avg_dq_rate > 0) 313 qdelay = (backlog << PIE_SCALE) / vars->avg_dq_rate; 314 else 315 qdelay = 0; 316 } else { 317 qdelay = vars->qdelay; 318 qdelay_old = vars->qdelay_old; 319 } 320 321 /* If qdelay is zero and backlog is not, it means backlog is very small, 322 * so we do not update probabilty in this round. 323 */ 324 if (qdelay == 0 && backlog != 0) 325 update_prob = false; 326 327 /* In the algorithm, alpha and beta are between 0 and 2 with typical 328 * value for alpha as 0.125. In this implementation, we use values 0-32 329 * passed from user space to represent this. Also, alpha and beta have 330 * unit of HZ and need to be scaled before they can used to update 331 * probability. alpha/beta are updated locally below by scaling down 332 * by 16 to come to 0-2 range. 333 */ 334 alpha = ((u64)params->alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4; 335 beta = ((u64)params->beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4; 336 337 /* We scale alpha and beta differently depending on how heavy the 338 * congestion is. Please see RFC 8033 for details. 339 */ 340 if (vars->prob < MAX_PROB / 10) { 341 alpha >>= 1; 342 beta >>= 1; 343 344 power = 100; 345 while (vars->prob < div_u64(MAX_PROB, power) && 346 power <= 1000000) { 347 alpha >>= 2; 348 beta >>= 2; 349 power *= 10; 350 } 351 } 352 353 /* alpha and beta should be between 0 and 32, in multiples of 1/16 */ 354 delta += alpha * (qdelay - params->target); 355 delta += beta * (qdelay - qdelay_old); 356 357 oldprob = vars->prob; 358 359 /* to ensure we increase probability in steps of no more than 2% */ 360 if (delta > (s64)(MAX_PROB / (100 / 2)) && 361 vars->prob >= MAX_PROB / 10) 362 delta = (MAX_PROB / 100) * 2; 363 364 /* Non-linear drop: 365 * Tune drop probability to increase quickly for high delays(>= 250ms) 366 * 250ms is derived through experiments and provides error protection 367 */ 368 369 if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC))) 370 delta += MAX_PROB / (100 / 2); 371 372 vars->prob += delta; 373 374 if (delta > 0) { 375 /* prevent overflow */ 376 if (vars->prob < oldprob) { 377 vars->prob = MAX_PROB; 378 /* Prevent normalization error. If probability is at 379 * maximum value already, we normalize it here, and 380 * skip the check to do a non-linear drop in the next 381 * section. 382 */ 383 update_prob = false; 384 } 385 } else { 386 /* prevent underflow */ 387 if (vars->prob > oldprob) 388 vars->prob = 0; 389 } 390 391 /* Non-linear drop in probability: Reduce drop probability quickly if 392 * delay is 0 for 2 consecutive Tupdate periods. 393 */ 394 395 if (qdelay == 0 && qdelay_old == 0 && update_prob) 396 /* Reduce drop probability to 98.4% */ 397 vars->prob -= vars->prob / 64; 398 399 vars->qdelay = qdelay; 400 vars->backlog_old = backlog; 401 402 /* We restart the measurement cycle if the following conditions are met 403 * 1. If the delay has been low for 2 consecutive Tupdate periods 404 * 2. Calculated drop probability is zero 405 * 3. If average dq_rate_estimator is enabled, we have at least one 406 * estimate for the avg_dq_rate ie., is a non-zero value 407 */ 408 if ((vars->qdelay < params->target / 2) && 409 (vars->qdelay_old < params->target / 2) && 410 vars->prob == 0 && 411 (!params->dq_rate_estimator || vars->avg_dq_rate > 0)) { 412 pie_vars_init(vars); 413 } 414 415 if (!params->dq_rate_estimator) 416 vars->qdelay_old = qdelay; 417 } 418 EXPORT_SYMBOL_GPL(pie_calculate_probability); 419 420 static void pie_timer(struct timer_list *t) 421 { 422 struct pie_sched_data *q = from_timer(q, t, adapt_timer); 423 struct Qdisc *sch = q->sch; 424 spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch)); 425 426 spin_lock(root_lock); 427 pie_calculate_probability(&q->params, &q->vars, sch->qstats.backlog); 428 429 /* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */ 430 if (q->params.tupdate) 431 mod_timer(&q->adapt_timer, jiffies + q->params.tupdate); 432 spin_unlock(root_lock); 433 } 434 435 static int pie_init(struct Qdisc *sch, struct nlattr *opt, 436 struct netlink_ext_ack *extack) 437 { 438 struct pie_sched_data *q = qdisc_priv(sch); 439 440 pie_params_init(&q->params); 441 pie_vars_init(&q->vars); 442 sch->limit = q->params.limit; 443 444 q->sch = sch; 445 timer_setup(&q->adapt_timer, pie_timer, 0); 446 447 if (opt) { 448 int err = pie_change(sch, opt, extack); 449 450 if (err) 451 return err; 452 } 453 454 mod_timer(&q->adapt_timer, jiffies + HZ / 2); 455 return 0; 456 } 457 458 static int pie_dump(struct Qdisc *sch, struct sk_buff *skb) 459 { 460 struct pie_sched_data *q = qdisc_priv(sch); 461 struct nlattr *opts; 462 463 opts = nla_nest_start_noflag(skb, TCA_OPTIONS); 464 if (!opts) 465 goto nla_put_failure; 466 467 /* convert target from pschedtime to us */ 468 if (nla_put_u32(skb, TCA_PIE_TARGET, 469 ((u32)PSCHED_TICKS2NS(q->params.target)) / 470 NSEC_PER_USEC) || 471 nla_put_u32(skb, TCA_PIE_LIMIT, sch->limit) || 472 nla_put_u32(skb, TCA_PIE_TUPDATE, 473 jiffies_to_usecs(q->params.tupdate)) || 474 nla_put_u32(skb, TCA_PIE_ALPHA, q->params.alpha) || 475 nla_put_u32(skb, TCA_PIE_BETA, q->params.beta) || 476 nla_put_u32(skb, TCA_PIE_ECN, q->params.ecn) || 477 nla_put_u32(skb, TCA_PIE_BYTEMODE, q->params.bytemode) || 478 nla_put_u32(skb, TCA_PIE_DQ_RATE_ESTIMATOR, 479 q->params.dq_rate_estimator)) 480 goto nla_put_failure; 481 482 return nla_nest_end(skb, opts); 483 484 nla_put_failure: 485 nla_nest_cancel(skb, opts); 486 return -1; 487 } 488 489 static 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 << BITS_PER_BYTE, 494 .delay = ((u32)PSCHED_TICKS2NS(q->vars.qdelay)) / 495 NSEC_PER_USEC, 496 .packets_in = q->stats.packets_in, 497 .overlimit = q->stats.overlimit, 498 .maxq = q->stats.maxq, 499 .dropped = q->stats.dropped, 500 .ecn_mark = q->stats.ecn_mark, 501 }; 502 503 /* avg_dq_rate is only valid if dq_rate_estimator is enabled */ 504 st.dq_rate_estimating = q->params.dq_rate_estimator; 505 506 /* unscale and return dq_rate in bytes per sec */ 507 if (q->params.dq_rate_estimator) 508 st.avg_dq_rate = q->vars.avg_dq_rate * 509 (PSCHED_TICKS_PER_SEC) >> PIE_SCALE; 510 511 return gnet_stats_copy_app(d, &st, sizeof(st)); 512 } 513 514 static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch) 515 { 516 struct pie_sched_data *q = qdisc_priv(sch); 517 struct sk_buff *skb = qdisc_dequeue_head(sch); 518 519 if (!skb) 520 return NULL; 521 522 pie_process_dequeue(skb, &q->params, &q->vars, sch->qstats.backlog); 523 return skb; 524 } 525 526 static void pie_reset(struct Qdisc *sch) 527 { 528 struct pie_sched_data *q = qdisc_priv(sch); 529 530 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); 537 538 q->params.tupdate = 0; 539 del_timer_sync(&q->adapt_timer); 540 } 541 542 static struct Qdisc_ops pie_qdisc_ops __read_mostly = { 543 .id = "pie", 544 .priv_size = sizeof(struct pie_sched_data), 545 .enqueue = pie_qdisc_enqueue, 546 .dequeue = pie_qdisc_dequeue, 547 .peek = qdisc_peek_dequeued, 548 .init = pie_init, 549 .destroy = pie_destroy, 550 .reset = pie_reset, 551 .change = pie_change, 552 .dump = pie_dump, 553 .dump_stats = pie_dump_stats, 554 .owner = THIS_MODULE, 555 }; 556 557 static int __init pie_module_init(void) 558 { 559 return register_qdisc(&pie_qdisc_ops); 560 } 561 562 static void __exit pie_module_exit(void) 563 { 564 unregister_qdisc(&pie_qdisc_ops); 565 } 566 567 module_init(pie_module_init); 568 module_exit(pie_module_exit); 569 570 MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler"); 571 MODULE_AUTHOR("Vijay Subramanian"); 572 MODULE_AUTHOR("Mythili Prabhu"); 573 MODULE_LICENSE("GPL"); 574