2 * Pluggable TCP congestion control support and newReno
4 * Based on ideas from I/O scheduler support and Web100.
6 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
9 #define pr_fmt(fmt) "TCP: " fmt
11 #include <linux/module.h>
13 #include <linux/types.h>
14 #include <linux/list.h>
15 #include <linux/gfp.h>
16 #include <linux/jhash.h>
19 static DEFINE_SPINLOCK(tcp_cong_list_lock);
20 static LIST_HEAD(tcp_cong_list);
22 /* Simple linear search, don't expect many entries! */
23 static struct tcp_congestion_ops *tcp_ca_find(const char *name)
25 struct tcp_congestion_ops *e;
27 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
28 if (strcmp(e->name, name) == 0)
35 /* Must be called with rcu lock held */
36 static const struct tcp_congestion_ops *__tcp_ca_find_autoload(const char *name)
38 const struct tcp_congestion_ops *ca = tcp_ca_find(name);
40 if (!ca && capable(CAP_NET_ADMIN)) {
42 request_module("tcp_%s", name);
44 ca = tcp_ca_find(name);
50 /* Simple linear search, not much in here. */
51 struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
53 struct tcp_congestion_ops *e;
55 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
64 * Attach new congestion control algorithm to the list
65 * of available options.
67 int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
71 /* all algorithms must implement these */
72 if (!ca->ssthresh || !ca->undo_cwnd ||
73 !(ca->cong_avoid || ca->cong_control)) {
74 pr_err("%s does not implement required ops\n", ca->name);
78 ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
80 spin_lock(&tcp_cong_list_lock);
81 if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
82 pr_notice("%s already registered or non-unique key\n",
86 list_add_tail_rcu(&ca->list, &tcp_cong_list);
87 pr_debug("%s registered\n", ca->name);
89 spin_unlock(&tcp_cong_list_lock);
93 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
96 * Remove congestion control algorithm, called from
97 * the module's remove function. Module ref counts are used
98 * to ensure that this can't be done till all sockets using
99 * that method are closed.
101 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
103 spin_lock(&tcp_cong_list_lock);
104 list_del_rcu(&ca->list);
105 spin_unlock(&tcp_cong_list_lock);
107 /* Wait for outstanding readers to complete before the
108 * module gets removed entirely.
110 * A try_module_get() should fail by now as our module is
111 * in "going" state since no refs are held anymore and
112 * module_exit() handler being called.
116 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
118 u32 tcp_ca_get_key_by_name(const char *name, bool *ecn_ca)
120 const struct tcp_congestion_ops *ca;
121 u32 key = TCP_CA_UNSPEC;
126 ca = __tcp_ca_find_autoload(name);
129 *ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
135 EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
137 char *tcp_ca_get_name_by_key(u32 key, char *buffer)
139 const struct tcp_congestion_ops *ca;
143 ca = tcp_ca_find_key(key);
145 ret = strncpy(buffer, ca->name,
151 EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
153 /* Assign choice of congestion control. */
154 void tcp_assign_congestion_control(struct sock *sk)
156 struct inet_connection_sock *icsk = inet_csk(sk);
157 struct tcp_congestion_ops *ca;
160 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
161 if (likely(try_module_get(ca->owner))) {
162 icsk->icsk_ca_ops = ca;
165 /* Fallback to next available. The last really
166 * guaranteed fallback is Reno from this list.
171 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
173 if (ca->flags & TCP_CONG_NEEDS_ECN)
176 INET_ECN_dontxmit(sk);
179 void tcp_init_congestion_control(struct sock *sk)
181 const struct inet_connection_sock *icsk = inet_csk(sk);
183 tcp_sk(sk)->prior_ssthresh = 0;
184 if (icsk->icsk_ca_ops->init)
185 icsk->icsk_ca_ops->init(sk);
186 if (tcp_ca_needs_ecn(sk))
189 INET_ECN_dontxmit(sk);
192 void tcp_reinit_congestion_control(struct sock *sk,
193 const struct tcp_congestion_ops *ca)
195 struct inet_connection_sock *icsk = inet_csk(sk);
197 tcp_cleanup_congestion_control(sk);
198 icsk->icsk_ca_ops = ca;
199 icsk->icsk_ca_setsockopt = 1;
200 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
202 if (sk->sk_state != TCP_CLOSE)
203 tcp_init_congestion_control(sk);
206 /* Manage refcounts on socket close. */
207 void tcp_cleanup_congestion_control(struct sock *sk)
209 struct inet_connection_sock *icsk = inet_csk(sk);
211 if (icsk->icsk_ca_ops->release)
212 icsk->icsk_ca_ops->release(sk);
213 module_put(icsk->icsk_ca_ops->owner);
216 /* Used by sysctl to change default congestion control */
217 int tcp_set_default_congestion_control(const char *name)
219 struct tcp_congestion_ops *ca;
222 spin_lock(&tcp_cong_list_lock);
223 ca = tcp_ca_find(name);
224 #ifdef CONFIG_MODULES
225 if (!ca && capable(CAP_NET_ADMIN)) {
226 spin_unlock(&tcp_cong_list_lock);
228 request_module("tcp_%s", name);
229 spin_lock(&tcp_cong_list_lock);
230 ca = tcp_ca_find(name);
235 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
236 list_move(&ca->list, &tcp_cong_list);
239 spin_unlock(&tcp_cong_list_lock);
244 /* Set default value from kernel configuration at bootup */
245 static int __init tcp_congestion_default(void)
247 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
249 late_initcall(tcp_congestion_default);
251 /* Build string with list of available congestion control values */
252 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
254 struct tcp_congestion_ops *ca;
258 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
259 offs += snprintf(buf + offs, maxlen - offs,
261 offs == 0 ? "" : " ", ca->name);
266 /* Get current default congestion control */
267 void tcp_get_default_congestion_control(char *name)
269 struct tcp_congestion_ops *ca;
270 /* We will always have reno... */
271 BUG_ON(list_empty(&tcp_cong_list));
274 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
275 strncpy(name, ca->name, TCP_CA_NAME_MAX);
279 /* Built list of non-restricted congestion control values */
280 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
282 struct tcp_congestion_ops *ca;
287 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
288 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
290 offs += snprintf(buf + offs, maxlen - offs,
292 offs == 0 ? "" : " ", ca->name);
297 /* Change list of non-restricted congestion control */
298 int tcp_set_allowed_congestion_control(char *val)
300 struct tcp_congestion_ops *ca;
301 char *saved_clone, *clone, *name;
304 saved_clone = clone = kstrdup(val, GFP_USER);
308 spin_lock(&tcp_cong_list_lock);
309 /* pass 1 check for bad entries */
310 while ((name = strsep(&clone, " ")) && *name) {
311 ca = tcp_ca_find(name);
318 /* pass 2 clear old values */
319 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
320 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
322 /* pass 3 mark as allowed */
323 while ((name = strsep(&val, " ")) && *name) {
324 ca = tcp_ca_find(name);
327 ca->flags |= TCP_CONG_NON_RESTRICTED;
330 spin_unlock(&tcp_cong_list_lock);
336 /* Change congestion control for socket. If load is false, then it is the
337 * responsibility of the caller to call tcp_init_congestion_control or
338 * tcp_reinit_congestion_control (if the current congestion control was
339 * already initialized.
341 int tcp_set_congestion_control(struct sock *sk, const char *name, bool load)
343 struct inet_connection_sock *icsk = inet_csk(sk);
344 const struct tcp_congestion_ops *ca;
347 if (icsk->icsk_ca_dst_locked)
352 ca = tcp_ca_find(name);
354 ca = __tcp_ca_find_autoload(name);
355 /* No change asking for existing value */
356 if (ca == icsk->icsk_ca_ops) {
357 icsk->icsk_ca_setsockopt = 1;
363 icsk->icsk_ca_ops = ca;
364 if (!try_module_get(ca->owner))
366 } else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
367 ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))) {
369 } else if (!try_module_get(ca->owner)) {
372 tcp_reinit_congestion_control(sk, ca);
379 /* Slow start is used when congestion window is no greater than the slow start
380 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
381 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
382 * something better;) a packet is only considered (s)acked in its entirety to
383 * defend the ACK attacks described in the RFC. Slow start processes a stretch
384 * ACK of degree N as if N acks of degree 1 are received back to back except
385 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
386 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
388 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
390 u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
392 acked -= cwnd - tp->snd_cwnd;
393 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
397 EXPORT_SYMBOL_GPL(tcp_slow_start);
399 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
400 * for every packet that was ACKed.
402 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
404 /* If credits accumulated at a higher w, apply them gently now. */
405 if (tp->snd_cwnd_cnt >= w) {
406 tp->snd_cwnd_cnt = 0;
410 tp->snd_cwnd_cnt += acked;
411 if (tp->snd_cwnd_cnt >= w) {
412 u32 delta = tp->snd_cwnd_cnt / w;
414 tp->snd_cwnd_cnt -= delta * w;
415 tp->snd_cwnd += delta;
417 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
419 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
422 * TCP Reno congestion control
423 * This is special case used for fallback as well.
425 /* This is Jacobson's slow start and congestion avoidance.
426 * SIGCOMM '88, p. 328.
428 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
430 struct tcp_sock *tp = tcp_sk(sk);
432 if (!tcp_is_cwnd_limited(sk))
435 /* In "safe" area, increase. */
436 if (tcp_in_slow_start(tp)) {
437 acked = tcp_slow_start(tp, acked);
441 /* In dangerous area, increase slowly. */
442 tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
444 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
446 /* Slow start threshold is half the congestion window (min 2) */
447 u32 tcp_reno_ssthresh(struct sock *sk)
449 const struct tcp_sock *tp = tcp_sk(sk);
451 return max(tp->snd_cwnd >> 1U, 2U);
453 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
455 u32 tcp_reno_undo_cwnd(struct sock *sk)
457 const struct tcp_sock *tp = tcp_sk(sk);
459 return max(tp->snd_cwnd, tp->snd_ssthresh << 1);
461 EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
463 struct tcp_congestion_ops tcp_reno = {
464 .flags = TCP_CONG_NON_RESTRICTED,
466 .owner = THIS_MODULE,
467 .ssthresh = tcp_reno_ssthresh,
468 .cong_avoid = tcp_reno_cong_avoid,
469 .undo_cwnd = tcp_reno_undo_cwnd,