xref: /openbmc/linux/net/ipv4/tcp_cong.c (revision a8f80e8f) 
1 /*
2  * Plugable TCP congestion control support and newReno
3  * congestion control.
4  * Based on ideas from I/O scheduler suport and Web100.
5  *
6  * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
7  */
8 
9 #include <linux/module.h>
10 #include <linux/mm.h>
11 #include <linux/types.h>
12 #include <linux/list.h>
13 #include <net/tcp.h>
14 
15 int sysctl_tcp_max_ssthresh = 0;
16 
17 static DEFINE_SPINLOCK(tcp_cong_list_lock);
18 static LIST_HEAD(tcp_cong_list);
19 
20 /* Simple linear search, don't expect many entries! */
21 static struct tcp_congestion_ops *tcp_ca_find(const char *name)
22 {
23 	struct tcp_congestion_ops *e;
24 
25 	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
26 		if (strcmp(e->name, name) == 0)
27 			return e;
28 	}
29 
30 	return NULL;
31 }
32 
33 /*
34  * Attach new congestion control algorithm to the list
35  * of available options.
36  */
37 int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
38 {
39 	int ret = 0;
40 
41 	/* all algorithms must implement ssthresh and cong_avoid ops */
42 	if (!ca->ssthresh || !ca->cong_avoid) {
43 		printk(KERN_ERR "TCP %s does not implement required ops\n",
44 		       ca->name);
45 		return -EINVAL;
46 	}
47 
48 	spin_lock(&tcp_cong_list_lock);
49 	if (tcp_ca_find(ca->name)) {
50 		printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
51 		ret = -EEXIST;
52 	} else {
53 		list_add_tail_rcu(&ca->list, &tcp_cong_list);
54 		printk(KERN_INFO "TCP %s registered\n", ca->name);
55 	}
56 	spin_unlock(&tcp_cong_list_lock);
57 
58 	return ret;
59 }
60 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
61 
62 /*
63  * Remove congestion control algorithm, called from
64  * the module's remove function.  Module ref counts are used
65  * to ensure that this can't be done till all sockets using
66  * that method are closed.
67  */
68 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
69 {
70 	spin_lock(&tcp_cong_list_lock);
71 	list_del_rcu(&ca->list);
72 	spin_unlock(&tcp_cong_list_lock);
73 }
74 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
75 
76 /* Assign choice of congestion control. */
77 void tcp_init_congestion_control(struct sock *sk)
78 {
79 	struct inet_connection_sock *icsk = inet_csk(sk);
80 	struct tcp_congestion_ops *ca;
81 
82 	/* if no choice made yet assign the current value set as default */
83 	if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
84 		rcu_read_lock();
85 		list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
86 			if (try_module_get(ca->owner)) {
87 				icsk->icsk_ca_ops = ca;
88 				break;
89 			}
90 
91 			/* fallback to next available */
92 		}
93 		rcu_read_unlock();
94 	}
95 
96 	if (icsk->icsk_ca_ops->init)
97 		icsk->icsk_ca_ops->init(sk);
98 }
99 
100 /* Manage refcounts on socket close. */
101 void tcp_cleanup_congestion_control(struct sock *sk)
102 {
103 	struct inet_connection_sock *icsk = inet_csk(sk);
104 
105 	if (icsk->icsk_ca_ops->release)
106 		icsk->icsk_ca_ops->release(sk);
107 	module_put(icsk->icsk_ca_ops->owner);
108 }
109 
110 /* Used by sysctl to change default congestion control */
111 int tcp_set_default_congestion_control(const char *name)
112 {
113 	struct tcp_congestion_ops *ca;
114 	int ret = -ENOENT;
115 
116 	spin_lock(&tcp_cong_list_lock);
117 	ca = tcp_ca_find(name);
118 #ifdef CONFIG_MODULES
119 	if (!ca && capable(CAP_NET_ADMIN)) {
120 		spin_unlock(&tcp_cong_list_lock);
121 
122 		request_module("tcp_%s", name);
123 		spin_lock(&tcp_cong_list_lock);
124 		ca = tcp_ca_find(name);
125 	}
126 #endif
127 
128 	if (ca) {
129 		ca->flags |= TCP_CONG_NON_RESTRICTED;	/* default is always allowed */
130 		list_move(&ca->list, &tcp_cong_list);
131 		ret = 0;
132 	}
133 	spin_unlock(&tcp_cong_list_lock);
134 
135 	return ret;
136 }
137 
138 /* Set default value from kernel configuration at bootup */
139 static int __init tcp_congestion_default(void)
140 {
141 	return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
142 }
143 late_initcall(tcp_congestion_default);
144 
145 
146 /* Build string with list of available congestion control values */
147 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
148 {
149 	struct tcp_congestion_ops *ca;
150 	size_t offs = 0;
151 
152 	rcu_read_lock();
153 	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
154 		offs += snprintf(buf + offs, maxlen - offs,
155 				 "%s%s",
156 				 offs == 0 ? "" : " ", ca->name);
157 
158 	}
159 	rcu_read_unlock();
160 }
161 
162 /* Get current default congestion control */
163 void tcp_get_default_congestion_control(char *name)
164 {
165 	struct tcp_congestion_ops *ca;
166 	/* We will always have reno... */
167 	BUG_ON(list_empty(&tcp_cong_list));
168 
169 	rcu_read_lock();
170 	ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
171 	strncpy(name, ca->name, TCP_CA_NAME_MAX);
172 	rcu_read_unlock();
173 }
174 
175 /* Built list of non-restricted congestion control values */
176 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
177 {
178 	struct tcp_congestion_ops *ca;
179 	size_t offs = 0;
180 
181 	*buf = '\0';
182 	rcu_read_lock();
183 	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
184 		if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
185 			continue;
186 		offs += snprintf(buf + offs, maxlen - offs,
187 				 "%s%s",
188 				 offs == 0 ? "" : " ", ca->name);
189 
190 	}
191 	rcu_read_unlock();
192 }
193 
194 /* Change list of non-restricted congestion control */
195 int tcp_set_allowed_congestion_control(char *val)
196 {
197 	struct tcp_congestion_ops *ca;
198 	char *clone, *name;
199 	int ret = 0;
200 
201 	clone = kstrdup(val, GFP_USER);
202 	if (!clone)
203 		return -ENOMEM;
204 
205 	spin_lock(&tcp_cong_list_lock);
206 	/* pass 1 check for bad entries */
207 	while ((name = strsep(&clone, " ")) && *name) {
208 		ca = tcp_ca_find(name);
209 		if (!ca) {
210 			ret = -ENOENT;
211 			goto out;
212 		}
213 	}
214 
215 	/* pass 2 clear old values */
216 	list_for_each_entry_rcu(ca, &tcp_cong_list, list)
217 		ca->flags &= ~TCP_CONG_NON_RESTRICTED;
218 
219 	/* pass 3 mark as allowed */
220 	while ((name = strsep(&val, " ")) && *name) {
221 		ca = tcp_ca_find(name);
222 		WARN_ON(!ca);
223 		if (ca)
224 			ca->flags |= TCP_CONG_NON_RESTRICTED;
225 	}
226 out:
227 	spin_unlock(&tcp_cong_list_lock);
228 
229 	return ret;
230 }
231 
232 
233 /* Change congestion control for socket */
234 int tcp_set_congestion_control(struct sock *sk, const char *name)
235 {
236 	struct inet_connection_sock *icsk = inet_csk(sk);
237 	struct tcp_congestion_ops *ca;
238 	int err = 0;
239 
240 	rcu_read_lock();
241 	ca = tcp_ca_find(name);
242 
243 	/* no change asking for existing value */
244 	if (ca == icsk->icsk_ca_ops)
245 		goto out;
246 
247 #ifdef CONFIG_MODULES
248 	/* not found attempt to autoload module */
249 	if (!ca && capable(CAP_NET_ADMIN)) {
250 		rcu_read_unlock();
251 		request_module("tcp_%s", name);
252 		rcu_read_lock();
253 		ca = tcp_ca_find(name);
254 	}
255 #endif
256 	if (!ca)
257 		err = -ENOENT;
258 
259 	else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || capable(CAP_NET_ADMIN)))
260 		err = -EPERM;
261 
262 	else if (!try_module_get(ca->owner))
263 		err = -EBUSY;
264 
265 	else {
266 		tcp_cleanup_congestion_control(sk);
267 		icsk->icsk_ca_ops = ca;
268 
269 		if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
270 			icsk->icsk_ca_ops->init(sk);
271 	}
272  out:
273 	rcu_read_unlock();
274 	return err;
275 }
276 
277 /* RFC2861 Check whether we are limited by application or congestion window
278  * This is the inverse of cwnd check in tcp_tso_should_defer
279  */
280 int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
281 {
282 	const struct tcp_sock *tp = tcp_sk(sk);
283 	u32 left;
284 
285 	if (in_flight >= tp->snd_cwnd)
286 		return 1;
287 
288 	left = tp->snd_cwnd - in_flight;
289 	if (sk_can_gso(sk) &&
290 	    left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
291 	    left * tp->mss_cache < sk->sk_gso_max_size)
292 		return 1;
293 	return left <= tcp_max_burst(tp);
294 }
295 EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
296 
297 /*
298  * Slow start is used when congestion window is less than slow start
299  * threshold. This version implements the basic RFC2581 version
300  * and optionally supports:
301  * 	RFC3742 Limited Slow Start  	  - growth limited to max_ssthresh
302  *	RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
303  */
304 void tcp_slow_start(struct tcp_sock *tp)
305 {
306 	int cnt; /* increase in packets */
307 
308 	/* RFC3465: ABC Slow start
309 	 * Increase only after a full MSS of bytes is acked
310 	 *
311 	 * TCP sender SHOULD increase cwnd by the number of
312 	 * previously unacknowledged bytes ACKed by each incoming
313 	 * acknowledgment, provided the increase is not more than L
314 	 */
315 	if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
316 		return;
317 
318 	if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
319 		cnt = sysctl_tcp_max_ssthresh >> 1;	/* limited slow start */
320 	else
321 		cnt = tp->snd_cwnd;			/* exponential increase */
322 
323 	/* RFC3465: ABC
324 	 * We MAY increase by 2 if discovered delayed ack
325 	 */
326 	if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
327 		cnt <<= 1;
328 	tp->bytes_acked = 0;
329 
330 	tp->snd_cwnd_cnt += cnt;
331 	while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
332 		tp->snd_cwnd_cnt -= tp->snd_cwnd;
333 		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
334 			tp->snd_cwnd++;
335 	}
336 }
337 EXPORT_SYMBOL_GPL(tcp_slow_start);
338 
339 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
340 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
341 {
342 	if (tp->snd_cwnd_cnt >= w) {
343 		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
344 			tp->snd_cwnd++;
345 		tp->snd_cwnd_cnt = 0;
346 	} else {
347 		tp->snd_cwnd_cnt++;
348 	}
349 }
350 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
351 
352 /*
353  * TCP Reno congestion control
354  * This is special case used for fallback as well.
355  */
356 /* This is Jacobson's slow start and congestion avoidance.
357  * SIGCOMM '88, p. 328.
358  */
359 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
360 {
361 	struct tcp_sock *tp = tcp_sk(sk);
362 
363 	if (!tcp_is_cwnd_limited(sk, in_flight))
364 		return;
365 
366 	/* In "safe" area, increase. */
367 	if (tp->snd_cwnd <= tp->snd_ssthresh)
368 		tcp_slow_start(tp);
369 
370 	/* In dangerous area, increase slowly. */
371 	else if (sysctl_tcp_abc) {
372 		/* RFC3465: Appropriate Byte Count
373 		 * increase once for each full cwnd acked
374 		 */
375 		if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
376 			tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
377 			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
378 				tp->snd_cwnd++;
379 		}
380 	} else {
381 		tcp_cong_avoid_ai(tp, tp->snd_cwnd);
382 	}
383 }
384 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
385 
386 /* Slow start threshold is half the congestion window (min 2) */
387 u32 tcp_reno_ssthresh(struct sock *sk)
388 {
389 	const struct tcp_sock *tp = tcp_sk(sk);
390 	return max(tp->snd_cwnd >> 1U, 2U);
391 }
392 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
393 
394 /* Lower bound on congestion window with halving. */
395 u32 tcp_reno_min_cwnd(const struct sock *sk)
396 {
397 	const struct tcp_sock *tp = tcp_sk(sk);
398 	return tp->snd_ssthresh/2;
399 }
400 EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
401 
402 struct tcp_congestion_ops tcp_reno = {
403 	.flags		= TCP_CONG_NON_RESTRICTED,
404 	.name		= "reno",
405 	.owner		= THIS_MODULE,
406 	.ssthresh	= tcp_reno_ssthresh,
407 	.cong_avoid	= tcp_reno_cong_avoid,
408 	.min_cwnd	= tcp_reno_min_cwnd,
409 };
410 
411 /* Initial congestion control used (until SYN)
412  * really reno under another name so we can tell difference
413  * during tcp_set_default_congestion_control
414  */
415 struct tcp_congestion_ops tcp_init_congestion_ops  = {
416 	.name		= "",
417 	.owner		= THIS_MODULE,
418 	.ssthresh	= tcp_reno_ssthresh,
419 	.cong_avoid	= tcp_reno_cong_avoid,
420 	.min_cwnd	= tcp_reno_min_cwnd,
421 };
422 EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);
423