xref: /openbmc/linux/net/sched/sch_cbs.c (revision e046fa89)
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 <net/netevent.h>
61 #include <net/netlink.h>
62 #include <net/sch_generic.h>
63 #include <net/pkt_sched.h>
64 
65 static LIST_HEAD(cbs_list);
66 static DEFINE_SPINLOCK(cbs_list_lock);
67 
68 #define BYTES_PER_KBIT (1000LL / 8)
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 
cbs_child_enqueue(struct sk_buff * skb,struct Qdisc * sch,struct Qdisc * child,struct sk_buff ** to_free)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 
cbs_enqueue_offload(struct sk_buff * skb,struct Qdisc * sch,struct sk_buff ** to_free)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 
cbs_enqueue_soft(struct sk_buff * skb,struct Qdisc * sch,struct sk_buff ** to_free)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 
cbs_enqueue(struct sk_buff * skb,struct Qdisc * sch,struct sk_buff ** to_free)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 */
timediff_to_credits(s64 timediff,s64 slope)140 static s64 timediff_to_credits(s64 timediff, s64 slope)
141 {
142 	return div64_s64(timediff * slope, NSEC_PER_SEC);
143 }
144 
delay_from_credits(s64 credits,s64 slope)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 
credits_from_len(unsigned int len,s64 slope,s64 port_rate)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 
cbs_child_dequeue(struct Qdisc * sch,struct Qdisc * child)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 
cbs_dequeue_soft(struct Qdisc * sch)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 
cbs_dequeue_offload(struct Qdisc * sch)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 
cbs_dequeue(struct Qdisc * sch)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 
cbs_disable_offload(struct net_device * dev,struct cbs_sched_data * q)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 
cbs_enable_offload(struct net_device * dev,struct cbs_sched_data * q,const struct tc_cbs_qopt * opt,struct netlink_ext_ack * extack)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 
cbs_set_port_rate(struct net_device * dev,struct cbs_sched_data * q)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 
cbs_dev_notifier(struct notifier_block * nb,unsigned long event,void * ptr)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 
cbs_change(struct Qdisc * sch,struct nlattr * opt,struct netlink_ext_ack * extack)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 	q->hicredit = qopt->hicredit;
393 	q->locredit = qopt->locredit;
394 	q->idleslope = qopt->idleslope * BYTES_PER_KBIT;
395 	q->sendslope = qopt->sendslope * BYTES_PER_KBIT;
396 	q->offload = qopt->offload;
397 
398 	return 0;
399 }
400 
cbs_init(struct Qdisc * sch,struct nlattr * opt,struct netlink_ext_ack * extack)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 
cbs_destroy(struct Qdisc * sch)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 
cbs_dump(struct Qdisc * sch,struct sk_buff * skb)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 = q->hicredit;
463 	opt.locredit = q->locredit;
464 	opt.sendslope = div64_s64(q->sendslope, BYTES_PER_KBIT);
465 	opt.idleslope = div64_s64(q->idleslope, BYTES_PER_KBIT);
466 	opt.offload = 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 
cbs_dump_class(struct Qdisc * sch,unsigned long cl,struct sk_buff * skb,struct tcmsg * tcm)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 
cbs_graft(struct Qdisc * sch,unsigned long arg,struct Qdisc * new,struct Qdisc ** old,struct netlink_ext_ack * extack)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 
cbs_leaf(struct Qdisc * sch,unsigned long arg)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 
cbs_find(struct Qdisc * sch,u32 classid)515 static unsigned long cbs_find(struct Qdisc *sch, u32 classid)
516 {
517 	return 1;
518 }
519 
cbs_walk(struct Qdisc * sch,struct qdisc_walker * walker)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 
550 static struct notifier_block cbs_device_notifier = {
551 	.notifier_call = cbs_dev_notifier,
552 };
553 
cbs_module_init(void)554 static int __init cbs_module_init(void)
555 {
556 	int err;
557 
558 	err = register_netdevice_notifier(&cbs_device_notifier);
559 	if (err)
560 		return err;
561 
562 	err = register_qdisc(&cbs_qdisc_ops);
563 	if (err)
564 		unregister_netdevice_notifier(&cbs_device_notifier);
565 
566 	return err;
567 }
568 
cbs_module_exit(void)569 static void __exit cbs_module_exit(void)
570 {
571 	unregister_qdisc(&cbs_qdisc_ops);
572 	unregister_netdevice_notifier(&cbs_device_notifier);
573 }
574 module_init(cbs_module_init)
575 module_exit(cbs_module_exit)
576 MODULE_LICENSE("GPL");
577