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 23 #define QUEUE_THRESHOLD 16384 24 #define DQCOUNT_INVALID -1 25 #define MAX_PROB 0xffffffffffffffff 26 #define PIE_SCALE 8 27 28 /* parameters used */ 29 struct pie_params { 30 psched_time_t target; /* user specified target delay in pschedtime */ 31 u32 tupdate; /* timer frequency (in jiffies) */ 32 u32 limit; /* number of packets that can be enqueued */ 33 u32 alpha; /* alpha and beta are between 0 and 32 */ 34 u32 beta; /* and are used for shift relative to 1 */ 35 bool ecn; /* true if ecn is enabled */ 36 bool bytemode; /* to scale drop early prob based on pkt size */ 37 }; 38 39 /* variables used */ 40 struct pie_vars { 41 u64 prob; /* probability but scaled by u64 limit. */ 42 psched_time_t burst_time; 43 psched_time_t qdelay; 44 psched_time_t qdelay_old; 45 u64 dq_count; /* measured in bytes */ 46 psched_time_t dq_tstamp; /* drain rate */ 47 u64 accu_prob; /* accumulated drop probability */ 48 u32 avg_dq_rate; /* bytes per pschedtime tick,scaled */ 49 u32 qlen_old; /* in bytes */ 50 u8 accu_prob_overflows; /* overflows of accu_prob */ 51 }; 52 53 /* statistics gathering */ 54 struct pie_stats { 55 u32 packets_in; /* total number of packets enqueued */ 56 u32 dropped; /* packets dropped due to pie_action */ 57 u32 overlimit; /* dropped due to lack of space in queue */ 58 u32 maxq; /* maximum queue size */ 59 u32 ecn_mark; /* packets marked with ECN */ 60 }; 61 62 /* private data for the Qdisc */ 63 struct pie_sched_data { 64 struct pie_params params; 65 struct pie_vars vars; 66 struct pie_stats stats; 67 struct timer_list adapt_timer; 68 struct Qdisc *sch; 69 }; 70 71 static void pie_params_init(struct pie_params *params) 72 { 73 params->alpha = 2; 74 params->beta = 20; 75 params->tupdate = usecs_to_jiffies(15 * USEC_PER_MSEC); /* 15 ms */ 76 params->limit = 1000; /* default of 1000 packets */ 77 params->target = PSCHED_NS2TICKS(15 * NSEC_PER_MSEC); /* 15 ms */ 78 params->ecn = false; 79 params->bytemode = false; 80 } 81 82 static void pie_vars_init(struct pie_vars *vars) 83 { 84 vars->dq_count = DQCOUNT_INVALID; 85 vars->accu_prob = 0; 86 vars->avg_dq_rate = 0; 87 /* default of 150 ms in pschedtime */ 88 vars->burst_time = PSCHED_NS2TICKS(150 * NSEC_PER_MSEC); 89 vars->accu_prob_overflows = 0; 90 } 91 92 static bool drop_early(struct Qdisc *sch, u32 packet_size) 93 { 94 struct pie_sched_data *q = qdisc_priv(sch); 95 u64 rnd; 96 u64 local_prob = q->vars.prob; 97 u32 mtu = psched_mtu(qdisc_dev(sch)); 98 99 /* If there is still burst allowance left skip random early drop */ 100 if (q->vars.burst_time > 0) 101 return false; 102 103 /* If current delay is less than half of target, and 104 * if drop prob is low already, disable early_drop 105 */ 106 if ((q->vars.qdelay < q->params.target / 2) && 107 (q->vars.prob < MAX_PROB / 5)) 108 return false; 109 110 /* If we have fewer than 2 mtu-sized packets, disable drop_early, 111 * similar to min_th in RED 112 */ 113 if (sch->qstats.backlog < 2 * mtu) 114 return false; 115 116 /* If bytemode is turned on, use packet size to compute new 117 * probablity. Smaller packets will have lower drop prob in this case 118 */ 119 if (q->params.bytemode && packet_size <= mtu) 120 local_prob = (u64)packet_size * div_u64(local_prob, mtu); 121 else 122 local_prob = q->vars.prob; 123 124 if (local_prob == 0) { 125 q->vars.accu_prob = 0; 126 q->vars.accu_prob_overflows = 0; 127 } 128 129 if (local_prob > MAX_PROB - q->vars.accu_prob) 130 q->vars.accu_prob_overflows++; 131 132 q->vars.accu_prob += local_prob; 133 134 if (q->vars.accu_prob_overflows == 0 && 135 q->vars.accu_prob < (MAX_PROB / 100) * 85) 136 return false; 137 if (q->vars.accu_prob_overflows == 8 && 138 q->vars.accu_prob >= MAX_PROB / 2) 139 return true; 140 141 prandom_bytes(&rnd, 8); 142 if (rnd < local_prob) { 143 q->vars.accu_prob = 0; 144 q->vars.accu_prob_overflows = 0; 145 return true; 146 } 147 148 return false; 149 } 150 151 static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch, 152 struct sk_buff **to_free) 153 { 154 struct pie_sched_data *q = qdisc_priv(sch); 155 bool enqueue = false; 156 157 if (unlikely(qdisc_qlen(sch) >= sch->limit)) { 158 q->stats.overlimit++; 159 goto out; 160 } 161 162 if (!drop_early(sch, skb->len)) { 163 enqueue = true; 164 } else if (q->params.ecn && (q->vars.prob <= MAX_PROB / 10) && 165 INET_ECN_set_ce(skb)) { 166 /* If packet is ecn capable, mark it if drop probability 167 * is lower than 10%, else drop it. 168 */ 169 q->stats.ecn_mark++; 170 enqueue = true; 171 } 172 173 /* we can enqueue the packet */ 174 if (enqueue) { 175 q->stats.packets_in++; 176 if (qdisc_qlen(sch) > q->stats.maxq) 177 q->stats.maxq = qdisc_qlen(sch); 178 179 return qdisc_enqueue_tail(skb, sch); 180 } 181 182 out: 183 q->stats.dropped++; 184 q->vars.accu_prob = 0; 185 q->vars.accu_prob_overflows = 0; 186 return qdisc_drop(skb, sch, to_free); 187 } 188 189 static const struct nla_policy pie_policy[TCA_PIE_MAX + 1] = { 190 [TCA_PIE_TARGET] = {.type = NLA_U32}, 191 [TCA_PIE_LIMIT] = {.type = NLA_U32}, 192 [TCA_PIE_TUPDATE] = {.type = NLA_U32}, 193 [TCA_PIE_ALPHA] = {.type = NLA_U32}, 194 [TCA_PIE_BETA] = {.type = NLA_U32}, 195 [TCA_PIE_ECN] = {.type = NLA_U32}, 196 [TCA_PIE_BYTEMODE] = {.type = NLA_U32}, 197 }; 198 199 static int pie_change(struct Qdisc *sch, struct nlattr *opt, 200 struct netlink_ext_ack *extack) 201 { 202 struct pie_sched_data *q = qdisc_priv(sch); 203 struct nlattr *tb[TCA_PIE_MAX + 1]; 204 unsigned int qlen, dropped = 0; 205 int err; 206 207 if (!opt) 208 return -EINVAL; 209 210 err = nla_parse_nested_deprecated(tb, TCA_PIE_MAX, opt, pie_policy, 211 NULL); 212 if (err < 0) 213 return err; 214 215 sch_tree_lock(sch); 216 217 /* convert from microseconds to pschedtime */ 218 if (tb[TCA_PIE_TARGET]) { 219 /* target is in us */ 220 u32 target = nla_get_u32(tb[TCA_PIE_TARGET]); 221 222 /* convert to pschedtime */ 223 q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC); 224 } 225 226 /* tupdate is in jiffies */ 227 if (tb[TCA_PIE_TUPDATE]) 228 q->params.tupdate = 229 usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE])); 230 231 if (tb[TCA_PIE_LIMIT]) { 232 u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]); 233 234 q->params.limit = limit; 235 sch->limit = limit; 236 } 237 238 if (tb[TCA_PIE_ALPHA]) 239 q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]); 240 241 if (tb[TCA_PIE_BETA]) 242 q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]); 243 244 if (tb[TCA_PIE_ECN]) 245 q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]); 246 247 if (tb[TCA_PIE_BYTEMODE]) 248 q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]); 249 250 /* Drop excess packets if new limit is lower */ 251 qlen = sch->q.qlen; 252 while (sch->q.qlen > sch->limit) { 253 struct sk_buff *skb = __qdisc_dequeue_head(&sch->q); 254 255 dropped += qdisc_pkt_len(skb); 256 qdisc_qstats_backlog_dec(sch, skb); 257 rtnl_qdisc_drop(skb, sch); 258 } 259 qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped); 260 261 sch_tree_unlock(sch); 262 return 0; 263 } 264 265 static void pie_process_dequeue(struct Qdisc *sch, struct sk_buff *skb) 266 { 267 struct pie_sched_data *q = qdisc_priv(sch); 268 int qlen = sch->qstats.backlog; /* current queue size in bytes */ 269 270 /* If current queue is about 10 packets or more and dq_count is unset 271 * we have enough packets to calculate the drain rate. Save 272 * current time as dq_tstamp and start measurement cycle. 273 */ 274 if (qlen >= QUEUE_THRESHOLD && q->vars.dq_count == DQCOUNT_INVALID) { 275 q->vars.dq_tstamp = psched_get_time(); 276 q->vars.dq_count = 0; 277 } 278 279 /* Calculate the average drain rate from this value. If queue length 280 * has receded to a small value viz., <= QUEUE_THRESHOLD bytes,reset 281 * the dq_count to -1 as we don't have enough packets to calculate the 282 * drain rate anymore The following if block is entered only when we 283 * have a substantial queue built up (QUEUE_THRESHOLD bytes or more) 284 * and we calculate the drain rate for the threshold here. dq_count is 285 * in bytes, time difference in psched_time, hence rate is in 286 * bytes/psched_time. 287 */ 288 if (q->vars.dq_count != DQCOUNT_INVALID) { 289 q->vars.dq_count += skb->len; 290 291 if (q->vars.dq_count >= QUEUE_THRESHOLD) { 292 psched_time_t now = psched_get_time(); 293 u32 dtime = now - q->vars.dq_tstamp; 294 u32 count = q->vars.dq_count << PIE_SCALE; 295 296 if (dtime == 0) 297 return; 298 299 count = count / dtime; 300 301 if (q->vars.avg_dq_rate == 0) 302 q->vars.avg_dq_rate = count; 303 else 304 q->vars.avg_dq_rate = 305 (q->vars.avg_dq_rate - 306 (q->vars.avg_dq_rate >> 3)) + (count >> 3); 307 308 /* If the queue has receded below the threshold, we hold 309 * on to the last drain rate calculated, else we reset 310 * dq_count to 0 to re-enter the if block when the next 311 * packet is dequeued 312 */ 313 if (qlen < QUEUE_THRESHOLD) { 314 q->vars.dq_count = DQCOUNT_INVALID; 315 } else { 316 q->vars.dq_count = 0; 317 q->vars.dq_tstamp = psched_get_time(); 318 } 319 320 if (q->vars.burst_time > 0) { 321 if (q->vars.burst_time > dtime) 322 q->vars.burst_time -= dtime; 323 else 324 q->vars.burst_time = 0; 325 } 326 } 327 } 328 } 329 330 static void calculate_probability(struct Qdisc *sch) 331 { 332 struct pie_sched_data *q = qdisc_priv(sch); 333 u32 qlen = sch->qstats.backlog; /* queue size in bytes */ 334 psched_time_t qdelay = 0; /* in pschedtime */ 335 psched_time_t qdelay_old = q->vars.qdelay; /* in pschedtime */ 336 s64 delta = 0; /* determines the change in probability */ 337 u64 oldprob; 338 u64 alpha, beta; 339 u32 power; 340 bool update_prob = true; 341 342 q->vars.qdelay_old = q->vars.qdelay; 343 344 if (q->vars.avg_dq_rate > 0) 345 qdelay = (qlen << PIE_SCALE) / q->vars.avg_dq_rate; 346 else 347 qdelay = 0; 348 349 /* If qdelay is zero and qlen is not, it means qlen is very small, less 350 * than dequeue_rate, so we do not update probabilty in this round 351 */ 352 if (qdelay == 0 && qlen != 0) 353 update_prob = false; 354 355 /* In the algorithm, alpha and beta are between 0 and 2 with typical 356 * value for alpha as 0.125. In this implementation, we use values 0-32 357 * passed from user space to represent this. Also, alpha and beta have 358 * unit of HZ and need to be scaled before they can used to update 359 * probability. alpha/beta are updated locally below by scaling down 360 * by 16 to come to 0-2 range. 361 */ 362 alpha = ((u64)q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4; 363 beta = ((u64)q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4; 364 365 /* We scale alpha and beta differently depending on how heavy the 366 * congestion is. Please see RFC 8033 for details. 367 */ 368 if (q->vars.prob < MAX_PROB / 10) { 369 alpha >>= 1; 370 beta >>= 1; 371 372 power = 100; 373 while (q->vars.prob < div_u64(MAX_PROB, power) && 374 power <= 1000000) { 375 alpha >>= 2; 376 beta >>= 2; 377 power *= 10; 378 } 379 } 380 381 /* alpha and beta should be between 0 and 32, in multiples of 1/16 */ 382 delta += alpha * (u64)(qdelay - q->params.target); 383 delta += beta * (u64)(qdelay - qdelay_old); 384 385 oldprob = q->vars.prob; 386 387 /* to ensure we increase probability in steps of no more than 2% */ 388 if (delta > (s64)(MAX_PROB / (100 / 2)) && 389 q->vars.prob >= MAX_PROB / 10) 390 delta = (MAX_PROB / 100) * 2; 391 392 /* Non-linear drop: 393 * Tune drop probability to increase quickly for high delays(>= 250ms) 394 * 250ms is derived through experiments and provides error protection 395 */ 396 397 if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC))) 398 delta += MAX_PROB / (100 / 2); 399 400 q->vars.prob += delta; 401 402 if (delta > 0) { 403 /* prevent overflow */ 404 if (q->vars.prob < oldprob) { 405 q->vars.prob = MAX_PROB; 406 /* Prevent normalization error. If probability is at 407 * maximum value already, we normalize it here, and 408 * skip the check to do a non-linear drop in the next 409 * section. 410 */ 411 update_prob = false; 412 } 413 } else { 414 /* prevent underflow */ 415 if (q->vars.prob > oldprob) 416 q->vars.prob = 0; 417 } 418 419 /* Non-linear drop in probability: Reduce drop probability quickly if 420 * delay is 0 for 2 consecutive Tupdate periods. 421 */ 422 423 if (qdelay == 0 && qdelay_old == 0 && update_prob) 424 /* Reduce drop probability to 98.4% */ 425 q->vars.prob -= q->vars.prob / 64u; 426 427 q->vars.qdelay = qdelay; 428 q->vars.qlen_old = qlen; 429 430 /* We restart the measurement cycle if the following conditions are met 431 * 1. If the delay has been low for 2 consecutive Tupdate periods 432 * 2. Calculated drop probability is zero 433 * 3. We have atleast one estimate for the avg_dq_rate ie., 434 * is a non-zero value 435 */ 436 if ((q->vars.qdelay < q->params.target / 2) && 437 (q->vars.qdelay_old < q->params.target / 2) && 438 q->vars.prob == 0 && 439 q->vars.avg_dq_rate > 0) 440 pie_vars_init(&q->vars); 441 } 442 443 static void pie_timer(struct timer_list *t) 444 { 445 struct pie_sched_data *q = from_timer(q, t, adapt_timer); 446 struct Qdisc *sch = q->sch; 447 spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch)); 448 449 spin_lock(root_lock); 450 calculate_probability(sch); 451 452 /* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */ 453 if (q->params.tupdate) 454 mod_timer(&q->adapt_timer, jiffies + q->params.tupdate); 455 spin_unlock(root_lock); 456 } 457 458 static int pie_init(struct Qdisc *sch, struct nlattr *opt, 459 struct netlink_ext_ack *extack) 460 { 461 struct pie_sched_data *q = qdisc_priv(sch); 462 463 pie_params_init(&q->params); 464 pie_vars_init(&q->vars); 465 sch->limit = q->params.limit; 466 467 q->sch = sch; 468 timer_setup(&q->adapt_timer, pie_timer, 0); 469 470 if (opt) { 471 int err = pie_change(sch, opt, extack); 472 473 if (err) 474 return err; 475 } 476 477 mod_timer(&q->adapt_timer, jiffies + HZ / 2); 478 return 0; 479 } 480 481 static int pie_dump(struct Qdisc *sch, struct sk_buff *skb) 482 { 483 struct pie_sched_data *q = qdisc_priv(sch); 484 struct nlattr *opts; 485 486 opts = nla_nest_start_noflag(skb, TCA_OPTIONS); 487 if (!opts) 488 goto nla_put_failure; 489 490 /* convert target from pschedtime to us */ 491 if (nla_put_u32(skb, TCA_PIE_TARGET, 492 ((u32)PSCHED_TICKS2NS(q->params.target)) / 493 NSEC_PER_USEC) || 494 nla_put_u32(skb, TCA_PIE_LIMIT, sch->limit) || 495 nla_put_u32(skb, TCA_PIE_TUPDATE, 496 jiffies_to_usecs(q->params.tupdate)) || 497 nla_put_u32(skb, TCA_PIE_ALPHA, q->params.alpha) || 498 nla_put_u32(skb, TCA_PIE_BETA, q->params.beta) || 499 nla_put_u32(skb, TCA_PIE_ECN, q->params.ecn) || 500 nla_put_u32(skb, TCA_PIE_BYTEMODE, q->params.bytemode)) 501 goto nla_put_failure; 502 503 return nla_nest_end(skb, opts); 504 505 nla_put_failure: 506 nla_nest_cancel(skb, opts); 507 return -1; 508 } 509 510 static int pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d) 511 { 512 struct pie_sched_data *q = qdisc_priv(sch); 513 struct tc_pie_xstats st = { 514 .prob = q->vars.prob, 515 .delay = ((u32)PSCHED_TICKS2NS(q->vars.qdelay)) / 516 NSEC_PER_USEC, 517 /* unscale and return dq_rate in bytes per sec */ 518 .avg_dq_rate = q->vars.avg_dq_rate * 519 (PSCHED_TICKS_PER_SEC) >> PIE_SCALE, 520 .packets_in = q->stats.packets_in, 521 .overlimit = q->stats.overlimit, 522 .maxq = q->stats.maxq, 523 .dropped = q->stats.dropped, 524 .ecn_mark = q->stats.ecn_mark, 525 }; 526 527 return gnet_stats_copy_app(d, &st, sizeof(st)); 528 } 529 530 static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch) 531 { 532 struct sk_buff *skb = qdisc_dequeue_head(sch); 533 534 if (!skb) 535 return NULL; 536 537 pie_process_dequeue(sch, skb); 538 return skb; 539 } 540 541 static void pie_reset(struct Qdisc *sch) 542 { 543 struct pie_sched_data *q = qdisc_priv(sch); 544 545 qdisc_reset_queue(sch); 546 pie_vars_init(&q->vars); 547 } 548 549 static void pie_destroy(struct Qdisc *sch) 550 { 551 struct pie_sched_data *q = qdisc_priv(sch); 552 553 q->params.tupdate = 0; 554 del_timer_sync(&q->adapt_timer); 555 } 556 557 static struct Qdisc_ops pie_qdisc_ops __read_mostly = { 558 .id = "pie", 559 .priv_size = sizeof(struct pie_sched_data), 560 .enqueue = pie_qdisc_enqueue, 561 .dequeue = pie_qdisc_dequeue, 562 .peek = qdisc_peek_dequeued, 563 .init = pie_init, 564 .destroy = pie_destroy, 565 .reset = pie_reset, 566 .change = pie_change, 567 .dump = pie_dump, 568 .dump_stats = pie_dump_stats, 569 .owner = THIS_MODULE, 570 }; 571 572 static int __init pie_module_init(void) 573 { 574 return register_qdisc(&pie_qdisc_ops); 575 } 576 577 static void __exit pie_module_exit(void) 578 { 579 unregister_qdisc(&pie_qdisc_ops); 580 } 581 582 module_init(pie_module_init); 583 module_exit(pie_module_exit); 584 585 MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler"); 586 MODULE_AUTHOR("Vijay Subramanian"); 587 MODULE_AUTHOR("Mythili Prabhu"); 588 MODULE_LICENSE("GPL"); 589