2 * Plugable TCP congestion control support and newReno
4 * Based on ideas from I/O scheduler suport and Web100.
6 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
9 #include <linux/module.h>
11 #include <linux/types.h>
12 #include <linux/list.h>
13 #include <linux/gfp.h>
16 int sysctl_tcp_max_ssthresh = 0;
18 static DEFINE_SPINLOCK(tcp_cong_list_lock);
19 static LIST_HEAD(tcp_cong_list);
21 /* Simple linear search, don't expect many entries! */
22 static struct tcp_congestion_ops *tcp_ca_find(const char *name)
24 struct tcp_congestion_ops *e;
26 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
27 if (strcmp(e->name, name) == 0)
35 * Attach new congestion control algorithm to the list
36 * of available options.
38 int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
42 /* all algorithms must implement ssthresh and cong_avoid ops */
43 if (!ca->ssthresh || !ca->cong_avoid) {
44 printk(KERN_ERR "TCP %s does not implement required ops\n",
49 spin_lock(&tcp_cong_list_lock);
50 if (tcp_ca_find(ca->name)) {
51 printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
54 list_add_tail_rcu(&ca->list, &tcp_cong_list);
55 printk(KERN_INFO "TCP %s registered\n", ca->name);
57 spin_unlock(&tcp_cong_list_lock);
61 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
64 * Remove congestion control algorithm, called from
65 * the module's remove function. Module ref counts are used
66 * to ensure that this can't be done till all sockets using
67 * that method are closed.
69 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
71 spin_lock(&tcp_cong_list_lock);
72 list_del_rcu(&ca->list);
73 spin_unlock(&tcp_cong_list_lock);
75 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
77 /* Assign choice of congestion control. */
78 void tcp_init_congestion_control(struct sock *sk)
80 struct inet_connection_sock *icsk = inet_csk(sk);
81 struct tcp_congestion_ops *ca;
83 /* if no choice made yet assign the current value set as default */
84 if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
86 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
87 if (try_module_get(ca->owner)) {
88 icsk->icsk_ca_ops = ca;
92 /* fallback to next available */
97 if (icsk->icsk_ca_ops->init)
98 icsk->icsk_ca_ops->init(sk);
101 /* Manage refcounts on socket close. */
102 void tcp_cleanup_congestion_control(struct sock *sk)
104 struct inet_connection_sock *icsk = inet_csk(sk);
106 if (icsk->icsk_ca_ops->release)
107 icsk->icsk_ca_ops->release(sk);
108 module_put(icsk->icsk_ca_ops->owner);
111 /* Used by sysctl to change default congestion control */
112 int tcp_set_default_congestion_control(const char *name)
114 struct tcp_congestion_ops *ca;
117 spin_lock(&tcp_cong_list_lock);
118 ca = tcp_ca_find(name);
119 #ifdef CONFIG_MODULES
120 if (!ca && capable(CAP_NET_ADMIN)) {
121 spin_unlock(&tcp_cong_list_lock);
123 request_module("tcp_%s", name);
124 spin_lock(&tcp_cong_list_lock);
125 ca = tcp_ca_find(name);
130 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
131 list_move(&ca->list, &tcp_cong_list);
134 spin_unlock(&tcp_cong_list_lock);
139 /* Set default value from kernel configuration at bootup */
140 static int __init tcp_congestion_default(void)
142 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
144 late_initcall(tcp_congestion_default);
147 /* Build string with list of available congestion control values */
148 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
150 struct tcp_congestion_ops *ca;
154 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
155 offs += snprintf(buf + offs, maxlen - offs,
157 offs == 0 ? "" : " ", ca->name);
163 /* Get current default congestion control */
164 void tcp_get_default_congestion_control(char *name)
166 struct tcp_congestion_ops *ca;
167 /* We will always have reno... */
168 BUG_ON(list_empty(&tcp_cong_list));
171 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
172 strncpy(name, ca->name, TCP_CA_NAME_MAX);
176 /* Built list of non-restricted congestion control values */
177 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
179 struct tcp_congestion_ops *ca;
184 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
185 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
187 offs += snprintf(buf + offs, maxlen - offs,
189 offs == 0 ? "" : " ", ca->name);
195 /* Change list of non-restricted congestion control */
196 int tcp_set_allowed_congestion_control(char *val)
198 struct tcp_congestion_ops *ca;
202 clone = kstrdup(val, GFP_USER);
206 spin_lock(&tcp_cong_list_lock);
207 /* pass 1 check for bad entries */
208 while ((name = strsep(&clone, " ")) && *name) {
209 ca = tcp_ca_find(name);
216 /* pass 2 clear old values */
217 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
218 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
220 /* pass 3 mark as allowed */
221 while ((name = strsep(&val, " ")) && *name) {
222 ca = tcp_ca_find(name);
225 ca->flags |= TCP_CONG_NON_RESTRICTED;
228 spin_unlock(&tcp_cong_list_lock);
234 /* Change congestion control for socket */
235 int tcp_set_congestion_control(struct sock *sk, const char *name)
237 struct inet_connection_sock *icsk = inet_csk(sk);
238 struct tcp_congestion_ops *ca;
242 ca = tcp_ca_find(name);
244 /* no change asking for existing value */
245 if (ca == icsk->icsk_ca_ops)
248 #ifdef CONFIG_MODULES
249 /* not found attempt to autoload module */
250 if (!ca && capable(CAP_NET_ADMIN)) {
252 request_module("tcp_%s", name);
254 ca = tcp_ca_find(name);
260 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || capable(CAP_NET_ADMIN)))
263 else if (!try_module_get(ca->owner))
267 tcp_cleanup_congestion_control(sk);
268 icsk->icsk_ca_ops = ca;
270 if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
271 icsk->icsk_ca_ops->init(sk);
278 /* RFC2861 Check whether we are limited by application or congestion window
279 * This is the inverse of cwnd check in tcp_tso_should_defer
281 int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
283 const struct tcp_sock *tp = tcp_sk(sk);
286 if (in_flight >= tp->snd_cwnd)
289 left = tp->snd_cwnd - in_flight;
290 if (sk_can_gso(sk) &&
291 left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
292 left * tp->mss_cache < sk->sk_gso_max_size)
294 return left <= tcp_max_burst(tp);
296 EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
299 * Slow start is used when congestion window is less than slow start
300 * threshold. This version implements the basic RFC2581 version
301 * and optionally supports:
302 * RFC3742 Limited Slow Start - growth limited to max_ssthresh
303 * RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
305 void tcp_slow_start(struct tcp_sock *tp)
307 int cnt; /* increase in packets */
309 /* RFC3465: ABC Slow start
310 * Increase only after a full MSS of bytes is acked
312 * TCP sender SHOULD increase cwnd by the number of
313 * previously unacknowledged bytes ACKed by each incoming
314 * acknowledgment, provided the increase is not more than L
316 if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
319 if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
320 cnt = sysctl_tcp_max_ssthresh >> 1; /* limited slow start */
322 cnt = tp->snd_cwnd; /* exponential increase */
325 * We MAY increase by 2 if discovered delayed ack
327 if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
331 tp->snd_cwnd_cnt += cnt;
332 while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
333 tp->snd_cwnd_cnt -= tp->snd_cwnd;
334 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
338 EXPORT_SYMBOL_GPL(tcp_slow_start);
340 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
341 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
343 if (tp->snd_cwnd_cnt >= w) {
344 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
346 tp->snd_cwnd_cnt = 0;
351 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
354 * TCP Reno congestion control
355 * This is special case used for fallback as well.
357 /* This is Jacobson's slow start and congestion avoidance.
358 * SIGCOMM '88, p. 328.
360 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
362 struct tcp_sock *tp = tcp_sk(sk);
364 if (!tcp_is_cwnd_limited(sk, in_flight))
367 /* In "safe" area, increase. */
368 if (tp->snd_cwnd <= tp->snd_ssthresh)
371 /* In dangerous area, increase slowly. */
372 else if (sysctl_tcp_abc) {
373 /* RFC3465: Appropriate Byte Count
374 * increase once for each full cwnd acked
376 if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
377 tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
378 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
382 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
385 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
387 /* Slow start threshold is half the congestion window (min 2) */
388 u32 tcp_reno_ssthresh(struct sock *sk)
390 const struct tcp_sock *tp = tcp_sk(sk);
391 return max(tp->snd_cwnd >> 1U, 2U);
393 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
395 /* Lower bound on congestion window with halving. */
396 u32 tcp_reno_min_cwnd(const struct sock *sk)
398 const struct tcp_sock *tp = tcp_sk(sk);
399 return tp->snd_ssthresh/2;
401 EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
403 struct tcp_congestion_ops tcp_reno = {
404 .flags = TCP_CONG_NON_RESTRICTED,
406 .owner = THIS_MODULE,
407 .ssthresh = tcp_reno_ssthresh,
408 .cong_avoid = tcp_reno_cong_avoid,
409 .min_cwnd = tcp_reno_min_cwnd,
412 /* Initial congestion control used (until SYN)
413 * really reno under another name so we can tell difference
414 * during tcp_set_default_congestion_control
416 struct tcp_congestion_ops tcp_init_congestion_ops = {
418 .owner = THIS_MODULE,
419 .ssthresh = tcp_reno_ssthresh,
420 .cong_avoid = tcp_reno_cong_avoid,
421 .min_cwnd = tcp_reno_min_cwnd,
423 EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);