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
67static LIST_HEAD(cbs_list);
68static DEFINE_SPINLOCK(cbs_list_lock);
69
70struct 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
88static 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
105static 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
114static 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
131static 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 */
140static s64 timediff_to_credits(s64 timediff, s64 slope)
141{
142	return div64_s64(timediff * slope, NSEC_PER_SEC);
143}
144
145static 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
153static 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
161static 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
176static 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
231static 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
239static 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
246static const struct nla_policy cbs_policy[TCA_CBS_MAX + 1] = {
247	[TCA_CBS_PARMS]	= { .len = sizeof(struct tc_cbs_qopt) },
248};
249
250static 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
276static 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
309static 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
323skip:
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
332static 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
361static 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
401static 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
433static 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
452static 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
473nla_put_failure:
474	nla_nest_cancel(skb, nest);
475	return -1;
476}
477
478static 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
492static 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
508static 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
515static unsigned long cbs_find(struct Qdisc *sch, u32 classid)
516{
517	return 1;
518}
519
520static 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
527static 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
535static 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};
549MODULE_ALIAS_NET_SCH("cbs");
550
551static struct notifier_block cbs_device_notifier = {
552	.notifier_call = cbs_dev_notifier,
553};
554
555static 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
570static void __exit cbs_module_exit(void)
571{
572	unregister_qdisc(&cbs_qdisc_ops);
573	unregister_netdevice_notifier(&cbs_device_notifier);
574}
575module_init(cbs_module_init)
576module_exit(cbs_module_exit)
577MODULE_LICENSE("GPL");
578MODULE_DESCRIPTION("Credit Based shaper");
579