xref: /openbmc/linux/net/sched/sch_tbf.c (revision e9e8bcb8) 
1 /*
2  * net/sched/sch_tbf.c	Token Bucket Filter queue.
3  *
4  *		This program is free software; you can redistribute it and/or
5  *		modify it under the terms of the GNU General Public License
6  *		as published by the Free Software Foundation; either version
7  *		2 of the License, or (at your option) any later version.
8  *
9  * Authors:	Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
10  *		Dmitry Torokhov <dtor@mail.ru> - allow attaching inner qdiscs -
11  *						 original idea by Martin Devera
12  *
13  */
14 
15 #include <linux/module.h>
16 #include <linux/types.h>
17 #include <linux/kernel.h>
18 #include <linux/string.h>
19 #include <linux/errno.h>
20 #include <linux/skbuff.h>
21 #include <net/netlink.h>
22 #include <net/pkt_sched.h>
23 
24 
25 /*	Simple Token Bucket Filter.
26 	=======================================
27 
28 	SOURCE.
29 	-------
30 
31 	None.
32 
33 	Description.
34 	------------
35 
36 	A data flow obeys TBF with rate R and depth B, if for any
37 	time interval t_i...t_f the number of transmitted bits
38 	does not exceed B + R*(t_f-t_i).
39 
40 	Packetized version of this definition:
41 	The sequence of packets of sizes s_i served at moments t_i
42 	obeys TBF, if for any i<=k:
43 
44 	s_i+....+s_k <= B + R*(t_k - t_i)
45 
46 	Algorithm.
47 	----------
48 
49 	Let N(t_i) be B/R initially and N(t) grow continuously with time as:
50 
51 	N(t+delta) = min{B/R, N(t) + delta}
52 
53 	If the first packet in queue has length S, it may be
54 	transmitted only at the time t_* when S/R <= N(t_*),
55 	and in this case N(t) jumps:
56 
57 	N(t_* + 0) = N(t_* - 0) - S/R.
58 
59 
60 
61 	Actually, QoS requires two TBF to be applied to a data stream.
62 	One of them controls steady state burst size, another
63 	one with rate P (peak rate) and depth M (equal to link MTU)
64 	limits bursts at a smaller time scale.
65 
66 	It is easy to see that P>R, and B>M. If P is infinity, this double
67 	TBF is equivalent to a single one.
68 
69 	When TBF works in reshaping mode, latency is estimated as:
70 
71 	lat = max ((L-B)/R, (L-M)/P)
72 
73 
74 	NOTES.
75 	------
76 
77 	If TBF throttles, it starts a watchdog timer, which will wake it up
78 	when it is ready to transmit.
79 	Note that the minimal timer resolution is 1/HZ.
80 	If no new packets arrive during this period,
81 	or if the device is not awaken by EOI for some previous packet,
82 	TBF can stop its activity for 1/HZ.
83 
84 
85 	This means, that with depth B, the maximal rate is
86 
87 	R_crit = B*HZ
88 
89 	F.e. for 10Mbit ethernet and HZ=100 the minimal allowed B is ~10Kbytes.
90 
91 	Note that the peak rate TBF is much more tough: with MTU 1500
92 	P_crit = 150Kbytes/sec. So, if you need greater peak
93 	rates, use alpha with HZ=1000 :-)
94 
95 	With classful TBF, limit is just kept for backwards compatibility.
96 	It is passed to the default bfifo qdisc - if the inner qdisc is
97 	changed the limit is not effective anymore.
98 */
99 
100 struct tbf_sched_data {
101 /* Parameters */
102 	u32		limit;		/* Maximal length of backlog: bytes */
103 	u32		buffer;		/* Token bucket depth/rate: MUST BE >= MTU/B */
104 	u32		mtu;
105 	u32		max_size;
106 	struct qdisc_rate_table	*R_tab;
107 	struct qdisc_rate_table	*P_tab;
108 
109 /* Variables */
110 	long	tokens;			/* Current number of B tokens */
111 	long	ptokens;		/* Current number of P tokens */
112 	psched_time_t	t_c;		/* Time check-point */
113 	struct Qdisc	*qdisc;		/* Inner qdisc, default - bfifo queue */
114 	struct qdisc_watchdog watchdog;	/* Watchdog timer */
115 };
116 
117 #define L2T(q, L)   qdisc_l2t((q)->R_tab, L)
118 #define L2T_P(q, L) qdisc_l2t((q)->P_tab, L)
119 
120 static int tbf_enqueue(struct sk_buff *skb, struct Qdisc *sch)
121 {
122 	struct tbf_sched_data *q = qdisc_priv(sch);
123 	int ret;
124 
125 	if (qdisc_pkt_len(skb) > q->max_size)
126 		return qdisc_reshape_fail(skb, sch);
127 
128 	ret = qdisc_enqueue(skb, q->qdisc);
129 	if (ret != NET_XMIT_SUCCESS) {
130 		if (net_xmit_drop_count(ret))
131 			sch->qstats.drops++;
132 		return ret;
133 	}
134 
135 	sch->q.qlen++;
136 	return NET_XMIT_SUCCESS;
137 }
138 
139 static unsigned int tbf_drop(struct Qdisc *sch)
140 {
141 	struct tbf_sched_data *q = qdisc_priv(sch);
142 	unsigned int len = 0;
143 
144 	if (q->qdisc->ops->drop && (len = q->qdisc->ops->drop(q->qdisc)) != 0) {
145 		sch->q.qlen--;
146 		sch->qstats.drops++;
147 	}
148 	return len;
149 }
150 
151 static struct sk_buff *tbf_dequeue(struct Qdisc *sch)
152 {
153 	struct tbf_sched_data *q = qdisc_priv(sch);
154 	struct sk_buff *skb;
155 
156 	skb = q->qdisc->ops->peek(q->qdisc);
157 
158 	if (skb) {
159 		psched_time_t now;
160 		long toks;
161 		long ptoks = 0;
162 		unsigned int len = qdisc_pkt_len(skb);
163 
164 		now = psched_get_time();
165 		toks = psched_tdiff_bounded(now, q->t_c, q->buffer);
166 
167 		if (q->P_tab) {
168 			ptoks = toks + q->ptokens;
169 			if (ptoks > (long)q->mtu)
170 				ptoks = q->mtu;
171 			ptoks -= L2T_P(q, len);
172 		}
173 		toks += q->tokens;
174 		if (toks > (long)q->buffer)
175 			toks = q->buffer;
176 		toks -= L2T(q, len);
177 
178 		if ((toks|ptoks) >= 0) {
179 			skb = qdisc_dequeue_peeked(q->qdisc);
180 			if (unlikely(!skb))
181 				return NULL;
182 
183 			q->t_c = now;
184 			q->tokens = toks;
185 			q->ptokens = ptoks;
186 			sch->q.qlen--;
187 			qdisc_unthrottled(sch);
188 			qdisc_bstats_update(sch, skb);
189 			return skb;
190 		}
191 
192 		qdisc_watchdog_schedule(&q->watchdog,
193 					now + max_t(long, -toks, -ptoks));
194 
195 		/* Maybe we have a shorter packet in the queue,
196 		   which can be sent now. It sounds cool,
197 		   but, however, this is wrong in principle.
198 		   We MUST NOT reorder packets under these circumstances.
199 
200 		   Really, if we split the flow into independent
201 		   subflows, it would be a very good solution.
202 		   This is the main idea of all FQ algorithms
203 		   (cf. CSZ, HPFQ, HFSC)
204 		 */
205 
206 		sch->qstats.overlimits++;
207 	}
208 	return NULL;
209 }
210 
211 static void tbf_reset(struct Qdisc *sch)
212 {
213 	struct tbf_sched_data *q = qdisc_priv(sch);
214 
215 	qdisc_reset(q->qdisc);
216 	sch->q.qlen = 0;
217 	q->t_c = psched_get_time();
218 	q->tokens = q->buffer;
219 	q->ptokens = q->mtu;
220 	qdisc_watchdog_cancel(&q->watchdog);
221 }
222 
223 static const struct nla_policy tbf_policy[TCA_TBF_MAX + 1] = {
224 	[TCA_TBF_PARMS]	= { .len = sizeof(struct tc_tbf_qopt) },
225 	[TCA_TBF_RTAB]	= { .type = NLA_BINARY, .len = TC_RTAB_SIZE },
226 	[TCA_TBF_PTAB]	= { .type = NLA_BINARY, .len = TC_RTAB_SIZE },
227 };
228 
229 static int tbf_change(struct Qdisc *sch, struct nlattr *opt)
230 {
231 	int err;
232 	struct tbf_sched_data *q = qdisc_priv(sch);
233 	struct nlattr *tb[TCA_TBF_PTAB + 1];
234 	struct tc_tbf_qopt *qopt;
235 	struct qdisc_rate_table *rtab = NULL;
236 	struct qdisc_rate_table *ptab = NULL;
237 	struct Qdisc *child = NULL;
238 	int max_size, n;
239 
240 	err = nla_parse_nested(tb, TCA_TBF_PTAB, opt, tbf_policy);
241 	if (err < 0)
242 		return err;
243 
244 	err = -EINVAL;
245 	if (tb[TCA_TBF_PARMS] == NULL)
246 		goto done;
247 
248 	qopt = nla_data(tb[TCA_TBF_PARMS]);
249 	rtab = qdisc_get_rtab(&qopt->rate, tb[TCA_TBF_RTAB]);
250 	if (rtab == NULL)
251 		goto done;
252 
253 	if (qopt->peakrate.rate) {
254 		if (qopt->peakrate.rate > qopt->rate.rate)
255 			ptab = qdisc_get_rtab(&qopt->peakrate, tb[TCA_TBF_PTAB]);
256 		if (ptab == NULL)
257 			goto done;
258 	}
259 
260 	for (n = 0; n < 256; n++)
261 		if (rtab->data[n] > qopt->buffer)
262 			break;
263 	max_size = (n << qopt->rate.cell_log) - 1;
264 	if (ptab) {
265 		int size;
266 
267 		for (n = 0; n < 256; n++)
268 			if (ptab->data[n] > qopt->mtu)
269 				break;
270 		size = (n << qopt->peakrate.cell_log) - 1;
271 		if (size < max_size)
272 			max_size = size;
273 	}
274 	if (max_size < 0)
275 		goto done;
276 
277 	if (q->qdisc != &noop_qdisc) {
278 		err = fifo_set_limit(q->qdisc, qopt->limit);
279 		if (err)
280 			goto done;
281 	} else if (qopt->limit > 0) {
282 		child = fifo_create_dflt(sch, &bfifo_qdisc_ops, qopt->limit);
283 		if (IS_ERR(child)) {
284 			err = PTR_ERR(child);
285 			goto done;
286 		}
287 	}
288 
289 	sch_tree_lock(sch);
290 	if (child) {
291 		qdisc_tree_decrease_qlen(q->qdisc, q->qdisc->q.qlen);
292 		qdisc_destroy(q->qdisc);
293 		q->qdisc = child;
294 	}
295 	q->limit = qopt->limit;
296 	q->mtu = qopt->mtu;
297 	q->max_size = max_size;
298 	q->buffer = qopt->buffer;
299 	q->tokens = q->buffer;
300 	q->ptokens = q->mtu;
301 
302 	swap(q->R_tab, rtab);
303 	swap(q->P_tab, ptab);
304 
305 	sch_tree_unlock(sch);
306 	err = 0;
307 done:
308 	if (rtab)
309 		qdisc_put_rtab(rtab);
310 	if (ptab)
311 		qdisc_put_rtab(ptab);
312 	return err;
313 }
314 
315 static int tbf_init(struct Qdisc *sch, struct nlattr *opt)
316 {
317 	struct tbf_sched_data *q = qdisc_priv(sch);
318 
319 	if (opt == NULL)
320 		return -EINVAL;
321 
322 	q->t_c = psched_get_time();
323 	qdisc_watchdog_init(&q->watchdog, sch);
324 	q->qdisc = &noop_qdisc;
325 
326 	return tbf_change(sch, opt);
327 }
328 
329 static void tbf_destroy(struct Qdisc *sch)
330 {
331 	struct tbf_sched_data *q = qdisc_priv(sch);
332 
333 	qdisc_watchdog_cancel(&q->watchdog);
334 
335 	if (q->P_tab)
336 		qdisc_put_rtab(q->P_tab);
337 	if (q->R_tab)
338 		qdisc_put_rtab(q->R_tab);
339 
340 	qdisc_destroy(q->qdisc);
341 }
342 
343 static int tbf_dump(struct Qdisc *sch, struct sk_buff *skb)
344 {
345 	struct tbf_sched_data *q = qdisc_priv(sch);
346 	struct nlattr *nest;
347 	struct tc_tbf_qopt opt;
348 
349 	nest = nla_nest_start(skb, TCA_OPTIONS);
350 	if (nest == NULL)
351 		goto nla_put_failure;
352 
353 	opt.limit = q->limit;
354 	opt.rate = q->R_tab->rate;
355 	if (q->P_tab)
356 		opt.peakrate = q->P_tab->rate;
357 	else
358 		memset(&opt.peakrate, 0, sizeof(opt.peakrate));
359 	opt.mtu = q->mtu;
360 	opt.buffer = q->buffer;
361 	NLA_PUT(skb, TCA_TBF_PARMS, sizeof(opt), &opt);
362 
363 	nla_nest_end(skb, nest);
364 	return skb->len;
365 
366 nla_put_failure:
367 	nla_nest_cancel(skb, nest);
368 	return -1;
369 }
370 
371 static int tbf_dump_class(struct Qdisc *sch, unsigned long cl,
372 			  struct sk_buff *skb, struct tcmsg *tcm)
373 {
374 	struct tbf_sched_data *q = qdisc_priv(sch);
375 
376 	tcm->tcm_handle |= TC_H_MIN(1);
377 	tcm->tcm_info = q->qdisc->handle;
378 
379 	return 0;
380 }
381 
382 static int tbf_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new,
383 		     struct Qdisc **old)
384 {
385 	struct tbf_sched_data *q = qdisc_priv(sch);
386 
387 	if (new == NULL)
388 		new = &noop_qdisc;
389 
390 	sch_tree_lock(sch);
391 	*old = q->qdisc;
392 	q->qdisc = new;
393 	qdisc_tree_decrease_qlen(*old, (*old)->q.qlen);
394 	qdisc_reset(*old);
395 	sch_tree_unlock(sch);
396 
397 	return 0;
398 }
399 
400 static struct Qdisc *tbf_leaf(struct Qdisc *sch, unsigned long arg)
401 {
402 	struct tbf_sched_data *q = qdisc_priv(sch);
403 	return q->qdisc;
404 }
405 
406 static unsigned long tbf_get(struct Qdisc *sch, u32 classid)
407 {
408 	return 1;
409 }
410 
411 static void tbf_put(struct Qdisc *sch, unsigned long arg)
412 {
413 }
414 
415 static void tbf_walk(struct Qdisc *sch, struct qdisc_walker *walker)
416 {
417 	if (!walker->stop) {
418 		if (walker->count >= walker->skip)
419 			if (walker->fn(sch, 1, walker) < 0) {
420 				walker->stop = 1;
421 				return;
422 			}
423 		walker->count++;
424 	}
425 }
426 
427 static const struct Qdisc_class_ops tbf_class_ops = {
428 	.graft		=	tbf_graft,
429 	.leaf		=	tbf_leaf,
430 	.get		=	tbf_get,
431 	.put		=	tbf_put,
432 	.walk		=	tbf_walk,
433 	.dump		=	tbf_dump_class,
434 };
435 
436 static struct Qdisc_ops tbf_qdisc_ops __read_mostly = {
437 	.next		=	NULL,
438 	.cl_ops		=	&tbf_class_ops,
439 	.id		=	"tbf",
440 	.priv_size	=	sizeof(struct tbf_sched_data),
441 	.enqueue	=	tbf_enqueue,
442 	.dequeue	=	tbf_dequeue,
443 	.peek		=	qdisc_peek_dequeued,
444 	.drop		=	tbf_drop,
445 	.init		=	tbf_init,
446 	.reset		=	tbf_reset,
447 	.destroy	=	tbf_destroy,
448 	.change		=	tbf_change,
449 	.dump		=	tbf_dump,
450 	.owner		=	THIS_MODULE,
451 };
452 
453 static int __init tbf_module_init(void)
454 {
455 	return register_qdisc(&tbf_qdisc_ops);
456 }
457 
458 static void __exit tbf_module_exit(void)
459 {
460 	unregister_qdisc(&tbf_qdisc_ops);
461 }
462 module_init(tbf_module_init)
463 module_exit(tbf_module_exit)
464 MODULE_LICENSE("GPL");
465