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/ethtool.h>
54 #include <linux/module.h>
55 #include <linux/types.h>
56 #include <linux/kernel.h>
57 #include <linux/string.h>
58 #include <linux/errno.h>
59 #include <linux/skbuff.h>
60 #include <linux/units.h>
61
62 #include <net/netevent.h>
63 #include <net/netlink.h>
64 #include <net/sch_generic.h>
65 #include <net/pkt_sched.h>
66
67 static LIST_HEAD(cbs_list);
68 static DEFINE_SPINLOCK(cbs_list_lock);
69
70 struct cbs_sched_data {
71 bool offload;
72 int queue;
73 atomic64_t port_rate; /* in bytes/s */
74 s64 last; /* timestamp in ns */
75 s64 credits; /* in bytes */
76 s32 locredit; /* in bytes */
77 s32 hicredit; /* in bytes */
78 s64 sendslope; /* in bytes/s */
79 s64 idleslope; /* in bytes/s */
80 struct qdisc_watchdog watchdog;
81 int (*enqueue)(struct sk_buff *skb, struct Qdisc *sch,
82 struct sk_buff **to_free);
83 struct sk_buff *(*dequeue)(struct Qdisc *sch);
84 struct Qdisc *qdisc;
85 struct list_head cbs_list;
86 };
87
88 static int cbs_child_enqueue(struct sk_buff *skb, struct Qdisc *sch,
89 struct Qdisc *child,
90 struct sk_buff **to_free)
91 {
92 unsigned int len = qdisc_pkt_len(skb);
93 int err;
94
95 err = child->ops->enqueue(skb, child, to_free);
96 if (err != NET_XMIT_SUCCESS)
97 return err;
98
99 sch->qstats.backlog += len;
100 sch->q.qlen++;
101
102 return NET_XMIT_SUCCESS;
103 }
104
105 static int cbs_enqueue_offload(struct sk_buff *skb, struct Qdisc *sch,
106 struct sk_buff **to_free)
107 {
108 struct cbs_sched_data *q = qdisc_priv(sch);
109 struct Qdisc *qdisc = q->qdisc;
110
111 return cbs_child_enqueue(skb, sch, qdisc, to_free);
112 }
113
114 static int cbs_enqueue_soft(struct sk_buff *skb, struct Qdisc *sch,
115 struct sk_buff **to_free)
116 {
117 struct cbs_sched_data *q = qdisc_priv(sch);
118 struct Qdisc *qdisc = q->qdisc;
119
120 if (sch->q.qlen == 0 && q->credits > 0) {
121 /* We need to stop accumulating credits when there's
122 * no enqueued packets and q->credits is positive.
123 */
124 q->credits = 0;
125 q->last = ktime_get_ns();
126 }
127
128 return cbs_child_enqueue(skb, sch, qdisc, to_free);
129 }
130
131 static int cbs_enqueue(struct sk_buff *skb, struct Qdisc *sch,
132 struct sk_buff **to_free)
133 {
134 struct cbs_sched_data *q = qdisc_priv(sch);
135
136 return q->enqueue(skb, sch, to_free);
137 }
138
139 /* timediff is in ns, slope is in bytes/s */
140 static s64 timediff_to_credits(s64 timediff, s64 slope)
141 {
142 return div64_s64(timediff * slope, NSEC_PER_SEC);
143 }
144
145 static s64 delay_from_credits(s64 credits, s64 slope)
146 {
147 if (unlikely(slope == 0))
148 return S64_MAX;
149
150 return div64_s64(-credits * NSEC_PER_SEC, slope);
151 }
152
153 static s64 credits_from_len(unsigned int len, s64 slope, s64 port_rate)
154 {
155 if (unlikely(port_rate == 0))
156 return S64_MAX;
157
158 return div64_s64(len * slope, port_rate);
159 }
160
161 static struct sk_buff *cbs_child_dequeue(struct Qdisc *sch, struct Qdisc *child)
162 {
163 struct sk_buff *skb;
164
165 skb = child->ops->dequeue(child);
166 if (!skb)
167 return NULL;
168
169 qdisc_qstats_backlog_dec(sch, skb);
170 qdisc_bstats_update(sch, skb);
171 sch->q.qlen--;
172
173 return skb;
174 }
175
176 static struct sk_buff *cbs_dequeue_soft(struct Qdisc *sch)
177 {
178 struct cbs_sched_data *q = qdisc_priv(sch);
179 struct Qdisc *qdisc = q->qdisc;
180 s64 now = ktime_get_ns();
181 struct sk_buff *skb;
182 s64 credits;
183 int len;
184
185 /* The previous packet is still being sent */
186 if (now < q->last) {
187 qdisc_watchdog_schedule_ns(&q->watchdog, q->last);
188 return NULL;
189 }
190 if (q->credits < 0) {
191 credits = timediff_to_credits(now - q->last, q->idleslope);
192
193 credits = q->credits + credits;
194 q->credits = min_t(s64, credits, q->hicredit);
195
196 if (q->credits < 0) {
197 s64 delay;
198
199 delay = delay_from_credits(q->credits, q->idleslope);
200 qdisc_watchdog_schedule_ns(&q->watchdog, now + delay);
201
202 q->last = now;
203
204 return NULL;
205 }
206 }
207 skb = cbs_child_dequeue(sch, qdisc);
208 if (!skb)
209 return NULL;
210
211 len = qdisc_pkt_len(skb);
212
213 /* As sendslope is a negative number, this will decrease the
214 * amount of q->credits.
215 */
216 credits = credits_from_len(len, q->sendslope,
217 atomic64_read(&q->port_rate));
218 credits += q->credits;
219
220 q->credits = max_t(s64, credits, q->locredit);
221 /* Estimate of the transmission of the last byte of the packet in ns */
222 if (unlikely(atomic64_read(&q->port_rate) == 0))
223 q->last = now;
224 else
225 q->last = now + div64_s64(len * NSEC_PER_SEC,
226 atomic64_read(&q->port_rate));
227
228 return skb;
229 }
230
231 static struct sk_buff *cbs_dequeue_offload(struct Qdisc *sch)
232 {
233 struct cbs_sched_data *q = qdisc_priv(sch);
234 struct Qdisc *qdisc = q->qdisc;
235
236 return cbs_child_dequeue(sch, qdisc);
237 }
238
239 static struct sk_buff *cbs_dequeue(struct Qdisc *sch)
240 {
241 struct cbs_sched_data *q = qdisc_priv(sch);
242
243 return q->dequeue(sch);
244 }
245
246 static const struct nla_policy cbs_policy[TCA_CBS_MAX + 1] = {
247 [TCA_CBS_PARMS] = { .len = sizeof(struct tc_cbs_qopt) },
248 };
249
250 static void cbs_disable_offload(struct net_device *dev,
251 struct cbs_sched_data *q)
252 {
253 struct tc_cbs_qopt_offload cbs = { };
254 const struct net_device_ops *ops;
255 int err;
256
257 if (!q->offload)
258 return;
259
260 q->enqueue = cbs_enqueue_soft;
261 q->dequeue = cbs_dequeue_soft;
262
263 ops = dev->netdev_ops;
264 if (!ops->ndo_setup_tc)
265 return;
266
267 cbs.queue = q->queue;
268 cbs.enable = 0;
269
270 err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs);
271 if (err < 0)
272 pr_warn("Couldn't disable CBS offload for queue %d\n",
273 cbs.queue);
274 }
275
276 static int cbs_enable_offload(struct net_device *dev, struct cbs_sched_data *q,
277 const struct tc_cbs_qopt *opt,
278 struct netlink_ext_ack *extack)
279 {
280 const struct net_device_ops *ops = dev->netdev_ops;
281 struct tc_cbs_qopt_offload cbs = { };
282 int err;
283
284 if (!ops->ndo_setup_tc) {
285 NL_SET_ERR_MSG(extack, "Specified device does not support cbs offload");
286 return -EOPNOTSUPP;
287 }
288
289 cbs.queue = q->queue;
290
291 cbs.enable = 1;
292 cbs.hicredit = opt->hicredit;
293 cbs.locredit = opt->locredit;
294 cbs.idleslope = opt->idleslope;
295 cbs.sendslope = opt->sendslope;
296
297 err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs);
298 if (err < 0) {
299 NL_SET_ERR_MSG(extack, "Specified device failed to setup cbs hardware offload");
300 return err;
301 }
302
303 q->enqueue = cbs_enqueue_offload;
304 q->dequeue = cbs_dequeue_offload;
305
306 return 0;
307 }
308
309 static void cbs_set_port_rate(struct net_device *dev, struct cbs_sched_data *q)
310 {
311 struct ethtool_link_ksettings ecmd;
312 int speed = SPEED_10;
313 int port_rate;
314 int err;
315
316 err = __ethtool_get_link_ksettings(dev, &ecmd);
317 if (err < 0)
318 goto skip;
319
320 if (ecmd.base.speed && ecmd.base.speed != SPEED_UNKNOWN)
321 speed = ecmd.base.speed;
322
323 skip:
324 port_rate = speed * 1000 * BYTES_PER_KBIT;
325
326 atomic64_set(&q->port_rate, port_rate);
327 netdev_dbg(dev, "cbs: set %s's port_rate to: %lld, linkspeed: %d\n",
328 dev->name, (long long)atomic64_read(&q->port_rate),
329 ecmd.base.speed);
330 }
331
332 static int cbs_dev_notifier(struct notifier_block *nb, unsigned long event,
333 void *ptr)
334 {
335 struct net_device *dev = netdev_notifier_info_to_dev(ptr);
336 struct cbs_sched_data *q;
337 struct net_device *qdev;
338 bool found = false;
339
340 ASSERT_RTNL();
341
342 if (event != NETDEV_UP && event != NETDEV_CHANGE)
343 return NOTIFY_DONE;
344
345 spin_lock(&cbs_list_lock);
346 list_for_each_entry(q, &cbs_list, cbs_list) {
347 qdev = qdisc_dev(q->qdisc);
348 if (qdev == dev) {
349 found = true;
350 break;
351 }
352 }
353 spin_unlock(&cbs_list_lock);
354
355 if (found)
356 cbs_set_port_rate(dev, q);
357
358 return NOTIFY_DONE;
359 }
360
361 static int cbs_change(struct Qdisc *sch, struct nlattr *opt,
362 struct netlink_ext_ack *extack)
363 {
364 struct cbs_sched_data *q = qdisc_priv(sch);
365 struct net_device *dev = qdisc_dev(sch);
366 struct nlattr *tb[TCA_CBS_MAX + 1];
367 struct tc_cbs_qopt *qopt;
368 int err;
369
370 err = nla_parse_nested_deprecated(tb, TCA_CBS_MAX, opt, cbs_policy,
371 extack);
372 if (err < 0)
373 return err;
374
375 if (!tb[TCA_CBS_PARMS]) {
376 NL_SET_ERR_MSG(extack, "Missing CBS parameter which are mandatory");
377 return -EINVAL;
378 }
379
380 qopt = nla_data(tb[TCA_CBS_PARMS]);
381
382 if (!qopt->offload) {
383 cbs_set_port_rate(dev, q);
384 cbs_disable_offload(dev, q);
385 } else {
386 err = cbs_enable_offload(dev, q, qopt, extack);
387 if (err < 0)
388 return err;
389 }
390
391 /* Everything went OK, save the parameters used. */
392 WRITE_ONCE(q->hicredit, qopt->hicredit);
393 WRITE_ONCE(q->locredit, qopt->locredit);
394 WRITE_ONCE(q->idleslope, qopt->idleslope * BYTES_PER_KBIT);
395 WRITE_ONCE(q->sendslope, qopt->sendslope * BYTES_PER_KBIT);
396 WRITE_ONCE(q->offload, qopt->offload);
397
398 return 0;
399 }
400
401 static int cbs_init(struct Qdisc *sch, struct nlattr *opt,
402 struct netlink_ext_ack *extack)
403 {
404 struct cbs_sched_data *q = qdisc_priv(sch);
405 struct net_device *dev = qdisc_dev(sch);
406
407 if (!opt) {
408 NL_SET_ERR_MSG(extack, "Missing CBS qdisc options which are mandatory");
409 return -EINVAL;
410 }
411
412 q->qdisc = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
413 sch->handle, extack);
414 if (!q->qdisc)
415 return -ENOMEM;
416
417 spin_lock(&cbs_list_lock);
418 list_add(&q->cbs_list, &cbs_list);
419 spin_unlock(&cbs_list_lock);
420
421 qdisc_hash_add(q->qdisc, false);
422
423 q->queue = sch->dev_queue - netdev_get_tx_queue(dev, 0);
424
425 q->enqueue = cbs_enqueue_soft;
426 q->dequeue = cbs_dequeue_soft;
427
428 qdisc_watchdog_init(&q->watchdog, sch);
429
430 return cbs_change(sch, opt, extack);
431 }
432
433 static void cbs_destroy(struct Qdisc *sch)
434 {
435 struct cbs_sched_data *q = qdisc_priv(sch);
436 struct net_device *dev = qdisc_dev(sch);
437
438 /* Nothing to do if we couldn't create the underlying qdisc */
439 if (!q->qdisc)
440 return;
441
442 qdisc_watchdog_cancel(&q->watchdog);
443 cbs_disable_offload(dev, q);
444
445 spin_lock(&cbs_list_lock);
446 list_del(&q->cbs_list);
447 spin_unlock(&cbs_list_lock);
448
449 qdisc_put(q->qdisc);
450 }
451
452 static int cbs_dump(struct Qdisc *sch, struct sk_buff *skb)
453 {
454 struct cbs_sched_data *q = qdisc_priv(sch);
455 struct tc_cbs_qopt opt = { };
456 struct nlattr *nest;
457
458 nest = nla_nest_start_noflag(skb, TCA_OPTIONS);
459 if (!nest)
460 goto nla_put_failure;
461
462 opt.hicredit = READ_ONCE(q->hicredit);
463 opt.locredit = READ_ONCE(q->locredit);
464 opt.sendslope = div64_s64(READ_ONCE(q->sendslope), BYTES_PER_KBIT);
465 opt.idleslope = div64_s64(READ_ONCE(q->idleslope), BYTES_PER_KBIT);
466 opt.offload = READ_ONCE(q->offload);
467
468 if (nla_put(skb, TCA_CBS_PARMS, sizeof(opt), &opt))
469 goto nla_put_failure;
470
471 return nla_nest_end(skb, nest);
472
473 nla_put_failure:
474 nla_nest_cancel(skb, nest);
475 return -1;
476 }
477
478 static int cbs_dump_class(struct Qdisc *sch, unsigned long cl,
479 struct sk_buff *skb, struct tcmsg *tcm)
480 {
481 struct cbs_sched_data *q = qdisc_priv(sch);
482
483 if (cl != 1 || !q->qdisc) /* only one class */
484 return -ENOENT;
485
486 tcm->tcm_handle |= TC_H_MIN(1);
487 tcm->tcm_info = q->qdisc->handle;
488
489 return 0;
490 }
491
492 static int cbs_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new,
493 struct Qdisc **old, struct netlink_ext_ack *extack)
494 {
495 struct cbs_sched_data *q = qdisc_priv(sch);
496
497 if (!new) {
498 new = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
499 sch->handle, NULL);
500 if (!new)
501 new = &noop_qdisc;
502 }
503
504 *old = qdisc_replace(sch, new, &q->qdisc);
505 return 0;
506 }
507
508 static struct Qdisc *cbs_leaf(struct Qdisc *sch, unsigned long arg)
509 {
510 struct cbs_sched_data *q = qdisc_priv(sch);
511
512 return q->qdisc;
513 }
514
515 static unsigned long cbs_find(struct Qdisc *sch, u32 classid)
516 {
517 return 1;
518 }
519
520 static void cbs_walk(struct Qdisc *sch, struct qdisc_walker *walker)
521 {
522 if (!walker->stop) {
523 tc_qdisc_stats_dump(sch, 1, walker);
524 }
525 }
526
527 static const struct Qdisc_class_ops cbs_class_ops = {
528 .graft = cbs_graft,
529 .leaf = cbs_leaf,
530 .find = cbs_find,
531 .walk = cbs_walk,
532 .dump = cbs_dump_class,
533 };
534
535 static struct Qdisc_ops cbs_qdisc_ops __read_mostly = {
536 .id = "cbs",
537 .cl_ops = &cbs_class_ops,
538 .priv_size = sizeof(struct cbs_sched_data),
539 .enqueue = cbs_enqueue,
540 .dequeue = cbs_dequeue,
541 .peek = qdisc_peek_dequeued,
542 .init = cbs_init,
543 .reset = qdisc_reset_queue,
544 .destroy = cbs_destroy,
545 .change = cbs_change,
546 .dump = cbs_dump,
547 .owner = THIS_MODULE,
548 };
549 MODULE_ALIAS_NET_SCH("cbs");
550
551 static struct notifier_block cbs_device_notifier = {
552 .notifier_call = cbs_dev_notifier,
553 };
554
555 static int __init cbs_module_init(void)
556 {
557 int err;
558
559 err = register_netdevice_notifier(&cbs_device_notifier);
560 if (err)
561 return err;
562
563 err = register_qdisc(&cbs_qdisc_ops);
564 if (err)
565 unregister_netdevice_notifier(&cbs_device_notifier);
566
567 return err;
568 }
569
570 static void __exit cbs_module_exit(void)
571 {
572 unregister_qdisc(&cbs_qdisc_ops);
573 unregister_netdevice_notifier(&cbs_device_notifier);
574 }
575 module_init(cbs_module_init)
576 module_exit(cbs_module_exit)
577 MODULE_LICENSE("GPL");
578 MODULE_DESCRIPTION("Credit Based shaper");
579
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