root/net/sched/sch_cbs.c

DEFINITIONS

1. cbs_child_enqueue
2. cbs_enqueue_offload
3. cbs_enqueue_soft
4. cbs_enqueue
5. timediff_to_credits
6. delay_from_credits
7. credits_from_len
8. cbs_child_dequeue
9. cbs_dequeue_soft
10. cbs_dequeue_offload
11. cbs_dequeue
12. cbs_disable_offload
13. cbs_enable_offload
14. cbs_set_port_rate
15. cbs_dev_notifier
16. cbs_change
17. cbs_init
18. cbs_destroy
19. cbs_dump
20. cbs_dump_class
21. cbs_graft
22. cbs_leaf
23. cbs_find
24. cbs_walk
25. cbs_module_init
26. cbs_module_exit

   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         /* The previous packet is still being sent */
 185         if (now < q->last) {
 186                 qdisc_watchdog_schedule_ns(&q->watchdog, q->last);
 187                 return NULL;
 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         /* Estimate of the transmission of the last byte of the packet in ns */
 221         if (unlikely(atomic64_read(&q->port_rate) == 0))
 222                 q->last = now;
 223         else
 224                 q->last = now + div64_s64(len * NSEC_PER_SEC,
 225                                           atomic64_read(&q->port_rate));
 226 
 227         return skb;
 228 }
 229 
 230 static struct sk_buff *cbs_dequeue_offload(struct Qdisc *sch)
 231 {
 232         struct cbs_sched_data *q = qdisc_priv(sch);
 233         struct Qdisc *qdisc = q->qdisc;
 234 
 235         return cbs_child_dequeue(sch, qdisc);
 236 }
 237 
 238 static struct sk_buff *cbs_dequeue(struct Qdisc *sch)
 239 {
 240         struct cbs_sched_data *q = qdisc_priv(sch);
 241 
 242         return q->dequeue(sch);
 243 }
 244 
 245 static const struct nla_policy cbs_policy[TCA_CBS_MAX + 1] = {
 246         [TCA_CBS_PARMS] = { .len = sizeof(struct tc_cbs_qopt) },
 247 };
 248 
 249 static void cbs_disable_offload(struct net_device *dev,
 250                                 struct cbs_sched_data *q)
 251 {
 252         struct tc_cbs_qopt_offload cbs = { };
 253         const struct net_device_ops *ops;
 254         int err;
 255 
 256         if (!q->offload)
 257                 return;
 258 
 259         q->enqueue = cbs_enqueue_soft;
 260         q->dequeue = cbs_dequeue_soft;
 261 
 262         ops = dev->netdev_ops;
 263         if (!ops->ndo_setup_tc)
 264                 return;
 265 
 266         cbs.queue = q->queue;
 267         cbs.enable = 0;
 268 
 269         err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs);
 270         if (err < 0)
 271                 pr_warn("Couldn't disable CBS offload for queue %d\n",
 272                         cbs.queue);
 273 }
 274 
 275 static int cbs_enable_offload(struct net_device *dev, struct cbs_sched_data *q,
 276                               const struct tc_cbs_qopt *opt,
 277                               struct netlink_ext_ack *extack)
 278 {
 279         const struct net_device_ops *ops = dev->netdev_ops;
 280         struct tc_cbs_qopt_offload cbs = { };
 281         int err;
 282 
 283         if (!ops->ndo_setup_tc) {
 284                 NL_SET_ERR_MSG(extack, "Specified device does not support cbs offload");
 285                 return -EOPNOTSUPP;
 286         }
 287 
 288         cbs.queue = q->queue;
 289 
 290         cbs.enable = 1;
 291         cbs.hicredit = opt->hicredit;
 292         cbs.locredit = opt->locredit;
 293         cbs.idleslope = opt->idleslope;
 294         cbs.sendslope = opt->sendslope;
 295 
 296         err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs);
 297         if (err < 0) {
 298                 NL_SET_ERR_MSG(extack, "Specified device failed to setup cbs hardware offload");
 299                 return err;
 300         }
 301 
 302         q->enqueue = cbs_enqueue_offload;
 303         q->dequeue = cbs_dequeue_offload;
 304 
 305         return 0;
 306 }
 307 
 308 static void cbs_set_port_rate(struct net_device *dev, struct cbs_sched_data *q)
 309 {
 310         struct ethtool_link_ksettings ecmd;
 311         int speed = SPEED_10;
 312         int port_rate;
 313         int err;
 314 
 315         err = __ethtool_get_link_ksettings(dev, &ecmd);
 316         if (err < 0)
 317                 goto skip;
 318 
 319         if (ecmd.base.speed && ecmd.base.speed != SPEED_UNKNOWN)
 320                 speed = ecmd.base.speed;
 321 
 322 skip:
 323         port_rate = speed * 1000 * BYTES_PER_KBIT;
 324 
 325         atomic64_set(&q->port_rate, port_rate);
 326         netdev_dbg(dev, "cbs: set %s's port_rate to: %lld, linkspeed: %d\n",
 327                    dev->name, (long long)atomic64_read(&q->port_rate),
 328                    ecmd.base.speed);
 329 }
 330 
 331 static int cbs_dev_notifier(struct notifier_block *nb, unsigned long event,
 332                             void *ptr)
 333 {
 334         struct net_device *dev = netdev_notifier_info_to_dev(ptr);
 335         struct cbs_sched_data *q;
 336         struct net_device *qdev;
 337         bool found = false;
 338 
 339         ASSERT_RTNL();
 340 
 341         if (event != NETDEV_UP && event != NETDEV_CHANGE)
 342                 return NOTIFY_DONE;
 343 
 344         spin_lock(&cbs_list_lock);
 345         list_for_each_entry(q, &cbs_list, cbs_list) {
 346                 qdev = qdisc_dev(q->qdisc);
 347                 if (qdev == dev) {
 348                         found = true;
 349                         break;
 350                 }
 351         }
 352         spin_unlock(&cbs_list_lock);
 353 
 354         if (found)
 355                 cbs_set_port_rate(dev, q);
 356 
 357         return NOTIFY_DONE;
 358 }
 359 
 360 static int cbs_change(struct Qdisc *sch, struct nlattr *opt,
 361                       struct netlink_ext_ack *extack)
 362 {
 363         struct cbs_sched_data *q = qdisc_priv(sch);
 364         struct net_device *dev = qdisc_dev(sch);
 365         struct nlattr *tb[TCA_CBS_MAX + 1];
 366         struct tc_cbs_qopt *qopt;
 367         int err;
 368 
 369         err = nla_parse_nested_deprecated(tb, TCA_CBS_MAX, opt, cbs_policy,
 370                                           extack);
 371         if (err < 0)
 372                 return err;
 373 
 374         if (!tb[TCA_CBS_PARMS]) {
 375                 NL_SET_ERR_MSG(extack, "Missing CBS parameter which are mandatory");
 376                 return -EINVAL;
 377         }
 378 
 379         qopt = nla_data(tb[TCA_CBS_PARMS]);
 380 
 381         if (!qopt->offload) {
 382                 cbs_set_port_rate(dev, q);
 383                 cbs_disable_offload(dev, q);
 384         } else {
 385                 err = cbs_enable_offload(dev, q, qopt, extack);
 386                 if (err < 0)
 387                         return err;
 388         }
 389 
 390         /* Everything went OK, save the parameters used. */
 391         q->hicredit = qopt->hicredit;
 392         q->locredit = qopt->locredit;
 393         q->idleslope = qopt->idleslope * BYTES_PER_KBIT;
 394         q->sendslope = qopt->sendslope * BYTES_PER_KBIT;
 395         q->offload = qopt->offload;
 396 
 397         return 0;
 398 }
 399 
 400 static int cbs_init(struct Qdisc *sch, struct nlattr *opt,
 401                     struct netlink_ext_ack *extack)
 402 {
 403         struct cbs_sched_data *q = qdisc_priv(sch);
 404         struct net_device *dev = qdisc_dev(sch);
 405 
 406         if (!opt) {
 407                 NL_SET_ERR_MSG(extack, "Missing CBS qdisc options  which are mandatory");
 408                 return -EINVAL;
 409         }
 410 
 411         q->qdisc = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
 412                                      sch->handle, extack);
 413         if (!q->qdisc)
 414                 return -ENOMEM;
 415 
 416         spin_lock(&cbs_list_lock);
 417         list_add(&q->cbs_list, &cbs_list);
 418         spin_unlock(&cbs_list_lock);
 419 
 420         qdisc_hash_add(q->qdisc, false);
 421 
 422         q->queue = sch->dev_queue - netdev_get_tx_queue(dev, 0);
 423 
 424         q->enqueue = cbs_enqueue_soft;
 425         q->dequeue = cbs_dequeue_soft;
 426 
 427         qdisc_watchdog_init(&q->watchdog, sch);
 428 
 429         return cbs_change(sch, opt, extack);
 430 }
 431 
 432 static void cbs_destroy(struct Qdisc *sch)
 433 {
 434         struct cbs_sched_data *q = qdisc_priv(sch);
 435         struct net_device *dev = qdisc_dev(sch);
 436 
 437         /* Nothing to do if we couldn't create the underlying qdisc */
 438         if (!q->qdisc)
 439                 return;
 440 
 441         qdisc_watchdog_cancel(&q->watchdog);
 442         cbs_disable_offload(dev, q);
 443 
 444         spin_lock(&cbs_list_lock);
 445         list_del(&q->cbs_list);
 446         spin_unlock(&cbs_list_lock);
 447 
 448         qdisc_put(q->qdisc);
 449 }
 450 
 451 static int cbs_dump(struct Qdisc *sch, struct sk_buff *skb)
 452 {
 453         struct cbs_sched_data *q = qdisc_priv(sch);
 454         struct tc_cbs_qopt opt = { };
 455         struct nlattr *nest;
 456 
 457         nest = nla_nest_start_noflag(skb, TCA_OPTIONS);
 458         if (!nest)
 459                 goto nla_put_failure;
 460 
 461         opt.hicredit = q->hicredit;
 462         opt.locredit = q->locredit;
 463         opt.sendslope = div64_s64(q->sendslope, BYTES_PER_KBIT);
 464         opt.idleslope = div64_s64(q->idleslope, BYTES_PER_KBIT);
 465         opt.offload = q->offload;
 466 
 467         if (nla_put(skb, TCA_CBS_PARMS, sizeof(opt), &opt))
 468                 goto nla_put_failure;
 469 
 470         return nla_nest_end(skb, nest);
 471 
 472 nla_put_failure:
 473         nla_nest_cancel(skb, nest);
 474         return -1;
 475 }
 476 
 477 static int cbs_dump_class(struct Qdisc *sch, unsigned long cl,
 478                           struct sk_buff *skb, struct tcmsg *tcm)
 479 {
 480         struct cbs_sched_data *q = qdisc_priv(sch);
 481 
 482         if (cl != 1 || !q->qdisc)       /* only one class */
 483                 return -ENOENT;
 484 
 485         tcm->tcm_handle |= TC_H_MIN(1);
 486         tcm->tcm_info = q->qdisc->handle;
 487 
 488         return 0;
 489 }
 490 
 491 static int cbs_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new,
 492                      struct Qdisc **old, struct netlink_ext_ack *extack)
 493 {
 494         struct cbs_sched_data *q = qdisc_priv(sch);
 495 
 496         if (!new) {
 497                 new = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
 498                                         sch->handle, NULL);
 499                 if (!new)
 500                         new = &noop_qdisc;
 501         }
 502 
 503         *old = qdisc_replace(sch, new, &q->qdisc);
 504         return 0;
 505 }
 506 
 507 static struct Qdisc *cbs_leaf(struct Qdisc *sch, unsigned long arg)
 508 {
 509         struct cbs_sched_data *q = qdisc_priv(sch);
 510 
 511         return q->qdisc;
 512 }
 513 
 514 static unsigned long cbs_find(struct Qdisc *sch, u32 classid)
 515 {
 516         return 1;
 517 }
 518 
 519 static void cbs_walk(struct Qdisc *sch, struct qdisc_walker *walker)
 520 {
 521         if (!walker->stop) {
 522                 if (walker->count >= walker->skip) {
 523                         if (walker->fn(sch, 1, walker) < 0) {
 524                                 walker->stop = 1;
 525                                 return;
 526                         }
 527                 }
 528                 walker->count++;
 529         }
 530 }
 531 
 532 static const struct Qdisc_class_ops cbs_class_ops = {
 533         .graft          =       cbs_graft,
 534         .leaf           =       cbs_leaf,
 535         .find           =       cbs_find,
 536         .walk           =       cbs_walk,
 537         .dump           =       cbs_dump_class,
 538 };
 539 
 540 static struct Qdisc_ops cbs_qdisc_ops __read_mostly = {
 541         .id             =       "cbs",
 542         .cl_ops         =       &cbs_class_ops,
 543         .priv_size      =       sizeof(struct cbs_sched_data),
 544         .enqueue        =       cbs_enqueue,
 545         .dequeue        =       cbs_dequeue,
 546         .peek           =       qdisc_peek_dequeued,
 547         .init           =       cbs_init,
 548         .reset          =       qdisc_reset_queue,
 549         .destroy        =       cbs_destroy,
 550         .change         =       cbs_change,
 551         .dump           =       cbs_dump,
 552         .owner          =       THIS_MODULE,
 553 };
 554 
 555 static struct notifier_block cbs_device_notifier = {
 556         .notifier_call = cbs_dev_notifier,
 557 };
 558 
 559 static int __init cbs_module_init(void)
 560 {
 561         int err;
 562 
 563         err = register_netdevice_notifier(&cbs_device_notifier);
 564         if (err)
 565                 return err;
 566 
 567         err = register_qdisc(&cbs_qdisc_ops);
 568         if (err)
 569                 unregister_netdevice_notifier(&cbs_device_notifier);
 570 
 571         return err;
 572 }
 573 
 574 static void __exit cbs_module_exit(void)
 575 {
 576         unregister_qdisc(&cbs_qdisc_ops);
 577         unregister_netdevice_notifier(&cbs_device_notifier);
 578 }
 579 module_init(cbs_module_init)
 580 module_exit(cbs_module_exit)
 581 MODULE_LICENSE("GPL");