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 WRITE_ONCE(q->params.target, 160 PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC)); 161 } 162 163 /* tupdate is in jiffies */ 164 if (tb[TCA_PIE_TUPDATE]) 165 WRITE_ONCE(q->params.tupdate, 166 usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE]))); 167 168 if (tb[TCA_PIE_LIMIT]) { 169 u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]); 170 171 WRITE_ONCE(q->params.limit, limit); 172 WRITE_ONCE(sch->limit, limit); 173 } 174 175 if (tb[TCA_PIE_ALPHA]) 176 WRITE_ONCE(q->params.alpha, nla_get_u32(tb[TCA_PIE_ALPHA])); 177 178 if (tb[TCA_PIE_BETA]) 179 WRITE_ONCE(q->params.beta, nla_get_u32(tb[TCA_PIE_BETA])); 180 181 if (tb[TCA_PIE_ECN]) 182 WRITE_ONCE(q->params.ecn, nla_get_u32(tb[TCA_PIE_ECN])); 183 184 if (tb[TCA_PIE_BYTEMODE]) 185 WRITE_ONCE(q->params.bytemode, 186 nla_get_u32(tb[TCA_PIE_BYTEMODE])); 187 188 if (tb[TCA_PIE_DQ_RATE_ESTIMATOR]) 189 WRITE_ONCE(q->params.dq_rate_estimator, 190 nla_get_u32(tb[TCA_PIE_DQ_RATE_ESTIMATOR])); 191 192 /* Drop excess packets if new limit is lower */ 193 qlen = sch->q.qlen; 194 while (sch->q.qlen > sch->limit) { 195 struct sk_buff *skb = __qdisc_dequeue_head(&sch->q); 196 197 dropped += qdisc_pkt_len(skb); 198 qdisc_qstats_backlog_dec(sch, skb); 199 rtnl_qdisc_drop(skb, sch); 200 } 201 qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped); 202 203 sch_tree_unlock(sch); 204 return 0; 205 } 206 207 void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params, 208 struct pie_vars *vars, u32 backlog) 209 { 210 psched_time_t now = psched_get_time(); 211 u32 dtime = 0; 212 213 /* If dq_rate_estimator is disabled, calculate qdelay using the 214 * packet timestamp. 215 */ 216 if (!params->dq_rate_estimator) { 217 vars->qdelay = now - pie_get_enqueue_time(skb); 218 219 if (vars->dq_tstamp != DTIME_INVALID) 220 dtime = now - vars->dq_tstamp; 221 222 vars->dq_tstamp = now; 223 224 if (backlog == 0) 225 vars->qdelay = 0; 226 227 if (dtime == 0) 228 return; 229 230 goto burst_allowance_reduction; 231 } 232 233 /* If current queue is about 10 packets or more and dq_count is unset 234 * we have enough packets to calculate the drain rate. Save 235 * current time as dq_tstamp and start measurement cycle. 236 */ 237 if (backlog >= QUEUE_THRESHOLD && vars->dq_count == DQCOUNT_INVALID) { 238 vars->dq_tstamp = psched_get_time(); 239 vars->dq_count = 0; 240 } 241 242 /* Calculate the average drain rate from this value. If queue length 243 * has receded to a small value viz., <= QUEUE_THRESHOLD bytes, reset 244 * the dq_count to -1 as we don't have enough packets to calculate the 245 * drain rate anymore. The following if block is entered only when we 246 * have a substantial queue built up (QUEUE_THRESHOLD bytes or more) 247 * and we calculate the drain rate for the threshold here. dq_count is 248 * in bytes, time difference in psched_time, hence rate is in 249 * bytes/psched_time. 250 */ 251 if (vars->dq_count != DQCOUNT_INVALID) { 252 vars->dq_count += skb->len; 253 254 if (vars->dq_count >= QUEUE_THRESHOLD) { 255 u32 count = vars->dq_count << PIE_SCALE; 256 257 dtime = now - vars->dq_tstamp; 258 259 if (dtime == 0) 260 return; 261 262 count = count / dtime; 263 264 if (vars->avg_dq_rate == 0) 265 vars->avg_dq_rate = count; 266 else 267 vars->avg_dq_rate = 268 (vars->avg_dq_rate - 269 (vars->avg_dq_rate >> 3)) + (count >> 3); 270 271 /* If the queue has receded below the threshold, we hold 272 * on to the last drain rate calculated, else we reset 273 * dq_count to 0 to re-enter the if block when the next 274 * packet is dequeued 275 */ 276 if (backlog < QUEUE_THRESHOLD) { 277 vars->dq_count = DQCOUNT_INVALID; 278 } else { 279 vars->dq_count = 0; 280 vars->dq_tstamp = psched_get_time(); 281 } 282 283 goto burst_allowance_reduction; 284 } 285 } 286 287 return; 288 289 burst_allowance_reduction: 290 if (vars->burst_time > 0) { 291 if (vars->burst_time > dtime) 292 vars->burst_time -= dtime; 293 else 294 vars->burst_time = 0; 295 } 296 } 297 EXPORT_SYMBOL_GPL(pie_process_dequeue); 298 299 void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars, 300 u32 backlog) 301 { 302 psched_time_t qdelay = 0; /* in pschedtime */ 303 psched_time_t qdelay_old = 0; /* in pschedtime */ 304 s64 delta = 0; /* determines the change in probability */ 305 u64 oldprob; 306 u64 alpha, beta; 307 u32 power; 308 bool update_prob = true; 309 310 if (params->dq_rate_estimator) { 311 qdelay_old = vars->qdelay; 312 vars->qdelay_old = vars->qdelay; 313 314 if (vars->avg_dq_rate > 0) 315 qdelay = (backlog << PIE_SCALE) / vars->avg_dq_rate; 316 else 317 qdelay = 0; 318 } else { 319 qdelay = vars->qdelay; 320 qdelay_old = vars->qdelay_old; 321 } 322 323 /* If qdelay is zero and backlog is not, it means backlog is very small, 324 * so we do not update probability in this round. 325 */ 326 if (qdelay == 0 && backlog != 0) 327 update_prob = false; 328 329 /* In the algorithm, alpha and beta are between 0 and 2 with typical 330 * value for alpha as 0.125. In this implementation, we use values 0-32 331 * passed from user space to represent this. Also, alpha and beta have 332 * unit of HZ and need to be scaled before they can used to update 333 * probability. alpha/beta are updated locally below by scaling down 334 * by 16 to come to 0-2 range. 335 */ 336 alpha = ((u64)params->alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4; 337 beta = ((u64)params->beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4; 338 339 /* We scale alpha and beta differently depending on how heavy the 340 * congestion is. Please see RFC 8033 for details. 341 */ 342 if (vars->prob < MAX_PROB / 10) { 343 alpha >>= 1; 344 beta >>= 1; 345 346 power = 100; 347 while (vars->prob < div_u64(MAX_PROB, power) && 348 power <= 1000000) { 349 alpha >>= 2; 350 beta >>= 2; 351 power *= 10; 352 } 353 } 354 355 /* alpha and beta should be between 0 and 32, in multiples of 1/16 */ 356 delta += alpha * (qdelay - params->target); 357 delta += beta * (qdelay - qdelay_old); 358 359 oldprob = vars->prob; 360 361 /* to ensure we increase probability in steps of no more than 2% */ 362 if (delta > (s64)(MAX_PROB / (100 / 2)) && 363 vars->prob >= MAX_PROB / 10) 364 delta = (MAX_PROB / 100) * 2; 365 366 /* Non-linear drop: 367 * Tune drop probability to increase quickly for high delays(>= 250ms) 368 * 250ms is derived through experiments and provides error protection 369 */ 370 371 if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC))) 372 delta += MAX_PROB / (100 / 2); 373 374 vars->prob += delta; 375 376 if (delta > 0) { 377 /* prevent overflow */ 378 if (vars->prob < oldprob) { 379 vars->prob = MAX_PROB; 380 /* Prevent normalization error. If probability is at 381 * maximum value already, we normalize it here, and 382 * skip the check to do a non-linear drop in the next 383 * section. 384 */ 385 update_prob = false; 386 } 387 } else { 388 /* prevent underflow */ 389 if (vars->prob > oldprob) 390 vars->prob = 0; 391 } 392 393 /* Non-linear drop in probability: Reduce drop probability quickly if 394 * delay is 0 for 2 consecutive Tupdate periods. 395 */ 396 397 if (qdelay == 0 && qdelay_old == 0 && update_prob) 398 /* Reduce drop probability to 98.4% */ 399 vars->prob -= vars->prob / 64; 400 401 vars->qdelay = qdelay; 402 vars->backlog_old = backlog; 403 404 /* We restart the measurement cycle if the following conditions are met 405 * 1. If the delay has been low for 2 consecutive Tupdate periods 406 * 2. Calculated drop probability is zero 407 * 3. If average dq_rate_estimator is enabled, we have at least one 408 * estimate for the avg_dq_rate ie., is a non-zero value 409 */ 410 if ((vars->qdelay < params->target / 2) && 411 (vars->qdelay_old < params->target / 2) && 412 vars->prob == 0 && 413 (!params->dq_rate_estimator || vars->avg_dq_rate > 0)) { 414 pie_vars_init(vars); 415 } 416 417 if (!params->dq_rate_estimator) 418 vars->qdelay_old = qdelay; 419 } 420 EXPORT_SYMBOL_GPL(pie_calculate_probability); 421 422 static void pie_timer(struct timer_list *t) 423 { 424 struct pie_sched_data *q = from_timer(q, t, adapt_timer); 425 struct Qdisc *sch = q->sch; 426 spinlock_t *root_lock; 427 428 rcu_read_lock(); 429 root_lock = qdisc_lock(qdisc_root_sleeping(sch)); 430 spin_lock(root_lock); 431 pie_calculate_probability(&q->params, &q->vars, sch->qstats.backlog); 432 433 /* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */ 434 if (q->params.tupdate) 435 mod_timer(&q->adapt_timer, jiffies + q->params.tupdate); 436 spin_unlock(root_lock); 437 rcu_read_unlock(); 438 } 439 440 static int pie_init(struct Qdisc *sch, struct nlattr *opt, 441 struct netlink_ext_ack *extack) 442 { 443 struct pie_sched_data *q = qdisc_priv(sch); 444 445 pie_params_init(&q->params); 446 pie_vars_init(&q->vars); 447 sch->limit = q->params.limit; 448 449 q->sch = sch; 450 timer_setup(&q->adapt_timer, pie_timer, 0); 451 452 if (opt) { 453 int err = pie_change(sch, opt, extack); 454 455 if (err) 456 return err; 457 } 458 459 mod_timer(&q->adapt_timer, jiffies + HZ / 2); 460 return 0; 461 } 462 463 static int pie_dump(struct Qdisc *sch, struct sk_buff *skb) 464 { 465 struct pie_sched_data *q = qdisc_priv(sch); 466 struct nlattr *opts; 467 468 opts = nla_nest_start_noflag(skb, TCA_OPTIONS); 469 if (!opts) 470 goto nla_put_failure; 471 472 /* convert target from pschedtime to us */ 473 if (nla_put_u32(skb, TCA_PIE_TARGET, 474 ((u32)PSCHED_TICKS2NS(READ_ONCE(q->params.target))) / 475 NSEC_PER_USEC) || 476 nla_put_u32(skb, TCA_PIE_LIMIT, READ_ONCE(sch->limit)) || 477 nla_put_u32(skb, TCA_PIE_TUPDATE, 478 jiffies_to_usecs(READ_ONCE(q->params.tupdate))) || 479 nla_put_u32(skb, TCA_PIE_ALPHA, READ_ONCE(q->params.alpha)) || 480 nla_put_u32(skb, TCA_PIE_BETA, READ_ONCE(q->params.beta)) || 481 nla_put_u32(skb, TCA_PIE_ECN, q->params.ecn) || 482 nla_put_u32(skb, TCA_PIE_BYTEMODE, 483 READ_ONCE(q->params.bytemode)) || 484 nla_put_u32(skb, TCA_PIE_DQ_RATE_ESTIMATOR, 485 READ_ONCE(q->params.dq_rate_estimator))) 486 goto nla_put_failure; 487 488 return nla_nest_end(skb, opts); 489 490 nla_put_failure: 491 nla_nest_cancel(skb, opts); 492 return -1; 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 << BITS_PER_BYTE, 500 .delay = ((u32)PSCHED_TICKS2NS(q->vars.qdelay)) / 501 NSEC_PER_USEC, 502 .packets_in = q->stats.packets_in, 503 .overlimit = q->stats.overlimit, 504 .maxq = q->stats.maxq, 505 .dropped = q->stats.dropped, 506 .ecn_mark = q->stats.ecn_mark, 507 }; 508 509 /* avg_dq_rate is only valid if dq_rate_estimator is enabled */ 510 st.dq_rate_estimating = q->params.dq_rate_estimator; 511 512 /* unscale and return dq_rate in bytes per sec */ 513 if (q->params.dq_rate_estimator) 514 st.avg_dq_rate = q->vars.avg_dq_rate * 515 (PSCHED_TICKS_PER_SEC) >> PIE_SCALE; 516 517 return gnet_stats_copy_app(d, &st, sizeof(st)); 518 } 519 520 static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch) 521 { 522 struct pie_sched_data *q = qdisc_priv(sch); 523 struct sk_buff *skb = qdisc_dequeue_head(sch); 524 525 if (!skb) 526 return NULL; 527 528 pie_process_dequeue(skb, &q->params, &q->vars, sch->qstats.backlog); 529 return skb; 530 } 531 532 static void pie_reset(struct Qdisc *sch) 533 { 534 struct pie_sched_data *q = qdisc_priv(sch); 535 536 qdisc_reset_queue(sch); 537 pie_vars_init(&q->vars); 538 } 539 540 static void pie_destroy(struct Qdisc *sch) 541 { 542 struct pie_sched_data *q = qdisc_priv(sch); 543 544 q->params.tupdate = 0; 545 del_timer_sync(&q->adapt_timer); 546 } 547 548 static struct Qdisc_ops pie_qdisc_ops __read_mostly = { 549 .id = "pie", 550 .priv_size = sizeof(struct pie_sched_data), 551 .enqueue = pie_qdisc_enqueue, 552 .dequeue = pie_qdisc_dequeue, 553 .peek = qdisc_peek_dequeued, 554 .init = pie_init, 555 .destroy = pie_destroy, 556 .reset = pie_reset, 557 .change = pie_change, 558 .dump = pie_dump, 559 .dump_stats = pie_dump_stats, 560 .owner = THIS_MODULE, 561 }; 562 MODULE_ALIAS_NET_SCH("pie"); 563 564 static int __init pie_module_init(void) 565 { 566 return register_qdisc(&pie_qdisc_ops); 567 } 568 569 static void __exit pie_module_exit(void) 570 { 571 unregister_qdisc(&pie_qdisc_ops); 572 } 573 574 module_init(pie_module_init); 575 module_exit(pie_module_exit); 576 577 MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler"); 578 MODULE_AUTHOR("Vijay Subramanian"); 579 MODULE_AUTHOR("Mythili Prabhu"); 580 MODULE_LICENSE("GPL"); 581