1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * net/sched/sch_cbs.c Credit Based Shaper 4 * 5 * Authors: Vinicius Costa Gomes <vinicius.gomes@intel.com> 6 */ 7 8 /* Credit Based Shaper (CBS) 9 * ========================= 10 * 11 * This is a simple rate-limiting shaper aimed at TSN applications on 12 * systems with known traffic workloads. 13 * 14 * Its algorithm is defined by the IEEE 802.1Q-2014 Specification, 15 * Section 8.6.8.2, and explained in more detail in the Annex L of the 16 * same specification. 17 * 18 * There are four tunables to be considered: 19 * 20 * 'idleslope': Idleslope is the rate of credits that is 21 * accumulated (in kilobits per second) when there is at least 22 * one packet waiting for transmission. Packets are transmitted 23 * when the current value of credits is equal or greater than 24 * zero. When there is no packet to be transmitted the amount of 25 * credits is set to zero. This is the main tunable of the CBS 26 * algorithm. 27 * 28 * 'sendslope': 29 * Sendslope is the rate of credits that is depleted (it should be a 30 * negative number of kilobits per second) when a transmission is 31 * ocurring. It can be calculated as follows, (IEEE 802.1Q-2014 Section 32 * 8.6.8.2 item g): 33 * 34 * sendslope = idleslope - port_transmit_rate 35 * 36 * 'hicredit': Hicredit defines the maximum amount of credits (in 37 * bytes) that can be accumulated. Hicredit depends on the 38 * characteristics of interfering traffic, 39 * 'max_interference_size' is the maximum size of any burst of 40 * traffic that can delay the transmission of a frame that is 41 * available for transmission for this traffic class, (IEEE 42 * 802.1Q-2014 Annex L, Equation L-3): 43 * 44 * hicredit = max_interference_size * (idleslope / port_transmit_rate) 45 * 46 * 'locredit': Locredit is the minimum amount of credits that can 47 * be reached. It is a function of the traffic flowing through 48 * this qdisc (IEEE 802.1Q-2014 Annex L, Equation L-2): 49 * 50 * locredit = max_frame_size * (sendslope / port_transmit_rate) 51 */ 52 53 #include <linux/module.h> 54 #include <linux/types.h> 55 #include <linux/kernel.h> 56 #include <linux/string.h> 57 #include <linux/errno.h> 58 #include <linux/skbuff.h> 59 #include <net/netevent.h> 60 #include <net/netlink.h> 61 #include <net/sch_generic.h> 62 #include <net/pkt_sched.h> 63 64 static LIST_HEAD(cbs_list); 65 static DEFINE_SPINLOCK(cbs_list_lock); 66 67 #define BYTES_PER_KBIT (1000LL / 8) 68 69 struct cbs_sched_data { 70 bool offload; 71 int queue; 72 atomic64_t port_rate; /* in bytes/s */ 73 s64 last; /* timestamp in ns */ 74 s64 credits; /* in bytes */ 75 s32 locredit; /* in bytes */ 76 s32 hicredit; /* in bytes */ 77 s64 sendslope; /* in bytes/s */ 78 s64 idleslope; /* in bytes/s */ 79 struct qdisc_watchdog watchdog; 80 int (*enqueue)(struct sk_buff *skb, struct Qdisc *sch, 81 struct sk_buff **to_free); 82 struct sk_buff *(*dequeue)(struct Qdisc *sch); 83 struct Qdisc *qdisc; 84 struct list_head cbs_list; 85 }; 86 87 static int cbs_child_enqueue(struct sk_buff *skb, struct Qdisc *sch, 88 struct Qdisc *child, 89 struct sk_buff **to_free) 90 { 91 unsigned int len = qdisc_pkt_len(skb); 92 int err; 93 94 err = child->ops->enqueue(skb, child, to_free); 95 if (err != NET_XMIT_SUCCESS) 96 return err; 97 98 sch->qstats.backlog += len; 99 sch->q.qlen++; 100 101 return NET_XMIT_SUCCESS; 102 } 103 104 static int cbs_enqueue_offload(struct sk_buff *skb, struct Qdisc *sch, 105 struct sk_buff **to_free) 106 { 107 struct cbs_sched_data *q = qdisc_priv(sch); 108 struct Qdisc *qdisc = q->qdisc; 109 110 return cbs_child_enqueue(skb, sch, qdisc, to_free); 111 } 112 113 static int cbs_enqueue_soft(struct sk_buff *skb, struct Qdisc *sch, 114 struct sk_buff **to_free) 115 { 116 struct cbs_sched_data *q = qdisc_priv(sch); 117 struct Qdisc *qdisc = q->qdisc; 118 119 if (sch->q.qlen == 0 && q->credits > 0) { 120 /* We need to stop accumulating credits when there's 121 * no enqueued packets and q->credits is positive. 122 */ 123 q->credits = 0; 124 q->last = ktime_get_ns(); 125 } 126 127 return cbs_child_enqueue(skb, sch, qdisc, to_free); 128 } 129 130 static int cbs_enqueue(struct sk_buff *skb, struct Qdisc *sch, 131 struct sk_buff **to_free) 132 { 133 struct cbs_sched_data *q = qdisc_priv(sch); 134 135 return q->enqueue(skb, sch, to_free); 136 } 137 138 /* timediff is in ns, slope is in bytes/s */ 139 static s64 timediff_to_credits(s64 timediff, s64 slope) 140 { 141 return div64_s64(timediff * slope, NSEC_PER_SEC); 142 } 143 144 static s64 delay_from_credits(s64 credits, s64 slope) 145 { 146 if (unlikely(slope == 0)) 147 return S64_MAX; 148 149 return div64_s64(-credits * NSEC_PER_SEC, slope); 150 } 151 152 static s64 credits_from_len(unsigned int len, s64 slope, s64 port_rate) 153 { 154 if (unlikely(port_rate == 0)) 155 return S64_MAX; 156 157 return div64_s64(len * slope, port_rate); 158 } 159 160 static struct sk_buff *cbs_child_dequeue(struct Qdisc *sch, struct Qdisc *child) 161 { 162 struct sk_buff *skb; 163 164 skb = child->ops->dequeue(child); 165 if (!skb) 166 return NULL; 167 168 qdisc_qstats_backlog_dec(sch, skb); 169 qdisc_bstats_update(sch, skb); 170 sch->q.qlen--; 171 172 return skb; 173 } 174 175 static struct sk_buff *cbs_dequeue_soft(struct Qdisc *sch) 176 { 177 struct cbs_sched_data *q = qdisc_priv(sch); 178 struct Qdisc *qdisc = q->qdisc; 179 s64 now = ktime_get_ns(); 180 struct sk_buff *skb; 181 s64 credits; 182 int len; 183 184 if (atomic64_read(&q->port_rate) == -1) { 185 WARN_ONCE(1, "cbs: dequeue() called with unknown port rate."); 186 return NULL; 187 } 188 189 if (q->credits < 0) { 190 credits = timediff_to_credits(now - q->last, q->idleslope); 191 192 credits = q->credits + credits; 193 q->credits = min_t(s64, credits, q->hicredit); 194 195 if (q->credits < 0) { 196 s64 delay; 197 198 delay = delay_from_credits(q->credits, q->idleslope); 199 qdisc_watchdog_schedule_ns(&q->watchdog, now + delay); 200 201 q->last = now; 202 203 return NULL; 204 } 205 } 206 skb = cbs_child_dequeue(sch, qdisc); 207 if (!skb) 208 return NULL; 209 210 len = qdisc_pkt_len(skb); 211 212 /* As sendslope is a negative number, this will decrease the 213 * amount of q->credits. 214 */ 215 credits = credits_from_len(len, q->sendslope, 216 atomic64_read(&q->port_rate)); 217 credits += q->credits; 218 219 q->credits = max_t(s64, credits, q->locredit); 220 q->last = now; 221 222 return skb; 223 } 224 225 static struct sk_buff *cbs_dequeue_offload(struct Qdisc *sch) 226 { 227 struct cbs_sched_data *q = qdisc_priv(sch); 228 struct Qdisc *qdisc = q->qdisc; 229 230 return cbs_child_dequeue(sch, qdisc); 231 } 232 233 static struct sk_buff *cbs_dequeue(struct Qdisc *sch) 234 { 235 struct cbs_sched_data *q = qdisc_priv(sch); 236 237 return q->dequeue(sch); 238 } 239 240 static const struct nla_policy cbs_policy[TCA_CBS_MAX + 1] = { 241 [TCA_CBS_PARMS] = { .len = sizeof(struct tc_cbs_qopt) }, 242 }; 243 244 static void cbs_disable_offload(struct net_device *dev, 245 struct cbs_sched_data *q) 246 { 247 struct tc_cbs_qopt_offload cbs = { }; 248 const struct net_device_ops *ops; 249 int err; 250 251 if (!q->offload) 252 return; 253 254 q->enqueue = cbs_enqueue_soft; 255 q->dequeue = cbs_dequeue_soft; 256 257 ops = dev->netdev_ops; 258 if (!ops->ndo_setup_tc) 259 return; 260 261 cbs.queue = q->queue; 262 cbs.enable = 0; 263 264 err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs); 265 if (err < 0) 266 pr_warn("Couldn't disable CBS offload for queue %d\n", 267 cbs.queue); 268 } 269 270 static int cbs_enable_offload(struct net_device *dev, struct cbs_sched_data *q, 271 const struct tc_cbs_qopt *opt, 272 struct netlink_ext_ack *extack) 273 { 274 const struct net_device_ops *ops = dev->netdev_ops; 275 struct tc_cbs_qopt_offload cbs = { }; 276 int err; 277 278 if (!ops->ndo_setup_tc) { 279 NL_SET_ERR_MSG(extack, "Specified device does not support cbs offload"); 280 return -EOPNOTSUPP; 281 } 282 283 cbs.queue = q->queue; 284 285 cbs.enable = 1; 286 cbs.hicredit = opt->hicredit; 287 cbs.locredit = opt->locredit; 288 cbs.idleslope = opt->idleslope; 289 cbs.sendslope = opt->sendslope; 290 291 err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs); 292 if (err < 0) { 293 NL_SET_ERR_MSG(extack, "Specified device failed to setup cbs hardware offload"); 294 return err; 295 } 296 297 q->enqueue = cbs_enqueue_offload; 298 q->dequeue = cbs_dequeue_offload; 299 300 return 0; 301 } 302 303 static void cbs_set_port_rate(struct net_device *dev, struct cbs_sched_data *q) 304 { 305 struct ethtool_link_ksettings ecmd; 306 int port_rate = -1; 307 308 if (!__ethtool_get_link_ksettings(dev, &ecmd) && 309 ecmd.base.speed != SPEED_UNKNOWN) 310 port_rate = ecmd.base.speed * 1000 * BYTES_PER_KBIT; 311 312 atomic64_set(&q->port_rate, port_rate); 313 netdev_dbg(dev, "cbs: set %s's port_rate to: %lld, linkspeed: %d\n", 314 dev->name, (long long)atomic64_read(&q->port_rate), 315 ecmd.base.speed); 316 } 317 318 static int cbs_dev_notifier(struct notifier_block *nb, unsigned long event, 319 void *ptr) 320 { 321 struct net_device *dev = netdev_notifier_info_to_dev(ptr); 322 struct cbs_sched_data *q; 323 struct net_device *qdev; 324 bool found = false; 325 326 ASSERT_RTNL(); 327 328 if (event != NETDEV_UP && event != NETDEV_CHANGE) 329 return NOTIFY_DONE; 330 331 spin_lock(&cbs_list_lock); 332 list_for_each_entry(q, &cbs_list, cbs_list) { 333 qdev = qdisc_dev(q->qdisc); 334 if (qdev == dev) { 335 found = true; 336 break; 337 } 338 } 339 spin_unlock(&cbs_list_lock); 340 341 if (found) 342 cbs_set_port_rate(dev, q); 343 344 return NOTIFY_DONE; 345 } 346 347 static int cbs_change(struct Qdisc *sch, struct nlattr *opt, 348 struct netlink_ext_ack *extack) 349 { 350 struct cbs_sched_data *q = qdisc_priv(sch); 351 struct net_device *dev = qdisc_dev(sch); 352 struct nlattr *tb[TCA_CBS_MAX + 1]; 353 struct tc_cbs_qopt *qopt; 354 int err; 355 356 err = nla_parse_nested_deprecated(tb, TCA_CBS_MAX, opt, cbs_policy, 357 extack); 358 if (err < 0) 359 return err; 360 361 if (!tb[TCA_CBS_PARMS]) { 362 NL_SET_ERR_MSG(extack, "Missing CBS parameter which are mandatory"); 363 return -EINVAL; 364 } 365 366 qopt = nla_data(tb[TCA_CBS_PARMS]); 367 368 if (!qopt->offload) { 369 cbs_set_port_rate(dev, q); 370 cbs_disable_offload(dev, q); 371 } else { 372 err = cbs_enable_offload(dev, q, qopt, extack); 373 if (err < 0) 374 return err; 375 } 376 377 /* Everything went OK, save the parameters used. */ 378 q->hicredit = qopt->hicredit; 379 q->locredit = qopt->locredit; 380 q->idleslope = qopt->idleslope * BYTES_PER_KBIT; 381 q->sendslope = qopt->sendslope * BYTES_PER_KBIT; 382 q->offload = qopt->offload; 383 384 return 0; 385 } 386 387 static int cbs_init(struct Qdisc *sch, struct nlattr *opt, 388 struct netlink_ext_ack *extack) 389 { 390 struct cbs_sched_data *q = qdisc_priv(sch); 391 struct net_device *dev = qdisc_dev(sch); 392 int err; 393 394 if (!opt) { 395 NL_SET_ERR_MSG(extack, "Missing CBS qdisc options which are mandatory"); 396 return -EINVAL; 397 } 398 399 q->qdisc = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops, 400 sch->handle, extack); 401 if (!q->qdisc) 402 return -ENOMEM; 403 404 qdisc_hash_add(q->qdisc, false); 405 406 q->queue = sch->dev_queue - netdev_get_tx_queue(dev, 0); 407 408 q->enqueue = cbs_enqueue_soft; 409 q->dequeue = cbs_dequeue_soft; 410 411 qdisc_watchdog_init(&q->watchdog, sch); 412 413 err = cbs_change(sch, opt, extack); 414 if (err) 415 return err; 416 417 if (!q->offload) { 418 spin_lock(&cbs_list_lock); 419 list_add(&q->cbs_list, &cbs_list); 420 spin_unlock(&cbs_list_lock); 421 } 422 423 return 0; 424 } 425 426 static void cbs_destroy(struct Qdisc *sch) 427 { 428 struct cbs_sched_data *q = qdisc_priv(sch); 429 struct net_device *dev = qdisc_dev(sch); 430 431 spin_lock(&cbs_list_lock); 432 list_del(&q->cbs_list); 433 spin_unlock(&cbs_list_lock); 434 435 qdisc_watchdog_cancel(&q->watchdog); 436 cbs_disable_offload(dev, q); 437 438 if (q->qdisc) 439 qdisc_put(q->qdisc); 440 } 441 442 static int cbs_dump(struct Qdisc *sch, struct sk_buff *skb) 443 { 444 struct cbs_sched_data *q = qdisc_priv(sch); 445 struct tc_cbs_qopt opt = { }; 446 struct nlattr *nest; 447 448 nest = nla_nest_start_noflag(skb, TCA_OPTIONS); 449 if (!nest) 450 goto nla_put_failure; 451 452 opt.hicredit = q->hicredit; 453 opt.locredit = q->locredit; 454 opt.sendslope = div64_s64(q->sendslope, BYTES_PER_KBIT); 455 opt.idleslope = div64_s64(q->idleslope, BYTES_PER_KBIT); 456 opt.offload = q->offload; 457 458 if (nla_put(skb, TCA_CBS_PARMS, sizeof(opt), &opt)) 459 goto nla_put_failure; 460 461 return nla_nest_end(skb, nest); 462 463 nla_put_failure: 464 nla_nest_cancel(skb, nest); 465 return -1; 466 } 467 468 static int cbs_dump_class(struct Qdisc *sch, unsigned long cl, 469 struct sk_buff *skb, struct tcmsg *tcm) 470 { 471 struct cbs_sched_data *q = qdisc_priv(sch); 472 473 if (cl != 1 || !q->qdisc) /* only one class */ 474 return -ENOENT; 475 476 tcm->tcm_handle |= TC_H_MIN(1); 477 tcm->tcm_info = q->qdisc->handle; 478 479 return 0; 480 } 481 482 static int cbs_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new, 483 struct Qdisc **old, struct netlink_ext_ack *extack) 484 { 485 struct cbs_sched_data *q = qdisc_priv(sch); 486 487 if (!new) { 488 new = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops, 489 sch->handle, NULL); 490 if (!new) 491 new = &noop_qdisc; 492 } 493 494 *old = qdisc_replace(sch, new, &q->qdisc); 495 return 0; 496 } 497 498 static struct Qdisc *cbs_leaf(struct Qdisc *sch, unsigned long arg) 499 { 500 struct cbs_sched_data *q = qdisc_priv(sch); 501 502 return q->qdisc; 503 } 504 505 static unsigned long cbs_find(struct Qdisc *sch, u32 classid) 506 { 507 return 1; 508 } 509 510 static void cbs_walk(struct Qdisc *sch, struct qdisc_walker *walker) 511 { 512 if (!walker->stop) { 513 if (walker->count >= walker->skip) { 514 if (walker->fn(sch, 1, walker) < 0) { 515 walker->stop = 1; 516 return; 517 } 518 } 519 walker->count++; 520 } 521 } 522 523 static const struct Qdisc_class_ops cbs_class_ops = { 524 .graft = cbs_graft, 525 .leaf = cbs_leaf, 526 .find = cbs_find, 527 .walk = cbs_walk, 528 .dump = cbs_dump_class, 529 }; 530 531 static struct Qdisc_ops cbs_qdisc_ops __read_mostly = { 532 .id = "cbs", 533 .cl_ops = &cbs_class_ops, 534 .priv_size = sizeof(struct cbs_sched_data), 535 .enqueue = cbs_enqueue, 536 .dequeue = cbs_dequeue, 537 .peek = qdisc_peek_dequeued, 538 .init = cbs_init, 539 .reset = qdisc_reset_queue, 540 .destroy = cbs_destroy, 541 .change = cbs_change, 542 .dump = cbs_dump, 543 .owner = THIS_MODULE, 544 }; 545 546 static struct notifier_block cbs_device_notifier = { 547 .notifier_call = cbs_dev_notifier, 548 }; 549 550 static int __init cbs_module_init(void) 551 { 552 int err; 553 554 err = register_netdevice_notifier(&cbs_device_notifier); 555 if (err) 556 return err; 557 558 err = register_qdisc(&cbs_qdisc_ops); 559 if (err) 560 unregister_netdevice_notifier(&cbs_device_notifier); 561 562 return err; 563 } 564 565 static void __exit cbs_module_exit(void) 566 { 567 unregister_qdisc(&cbs_qdisc_ops); 568 unregister_netdevice_notifier(&cbs_device_notifier); 569 } 570 module_init(cbs_module_init) 571 module_exit(cbs_module_exit) 572 MODULE_LICENSE("GPL"); 573