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 ssthresh and cong_avoid ops */
72 if (!ca->ssthresh || !(ca->cong_avoid || ca->cong_control)) {
73 pr_err("%s does not implement required ops\n", ca->name);
77 ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
79 spin_lock(&tcp_cong_list_lock);
80 if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
81 pr_notice("%s already registered or non-unique key\n",
85 list_add_tail_rcu(&ca->list, &tcp_cong_list);
86 pr_debug("%s registered\n", ca->name);
88 spin_unlock(&tcp_cong_list_lock);
92 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
95 * Remove congestion control algorithm, called from
96 * the module's remove function. Module ref counts are used
97 * to ensure that this can't be done till all sockets using
98 * that method are closed.
100 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
102 spin_lock(&tcp_cong_list_lock);
103 list_del_rcu(&ca->list);
104 spin_unlock(&tcp_cong_list_lock);
106 /* Wait for outstanding readers to complete before the
107 * module gets removed entirely.
109 * A try_module_get() should fail by now as our module is
110 * in "going" state since no refs are held anymore and
111 * module_exit() handler being called.
115 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
117 u32 tcp_ca_get_key_by_name(const char *name, bool *ecn_ca)
119 const struct tcp_congestion_ops *ca;
120 u32 key = TCP_CA_UNSPEC;
125 ca = __tcp_ca_find_autoload(name);
128 *ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
134 EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
136 char *tcp_ca_get_name_by_key(u32 key, char *buffer)
138 const struct tcp_congestion_ops *ca;
142 ca = tcp_ca_find_key(key);
144 ret = strncpy(buffer, ca->name,
150 EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
152 /* Assign choice of congestion control. */
153 void tcp_assign_congestion_control(struct sock *sk)
155 struct inet_connection_sock *icsk = inet_csk(sk);
156 struct tcp_congestion_ops *ca;
159 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
160 if (likely(try_module_get(ca->owner))) {
161 icsk->icsk_ca_ops = ca;
164 /* Fallback to next available. The last really
165 * guaranteed fallback is Reno from this list.
170 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
172 if (ca->flags & TCP_CONG_NEEDS_ECN)
175 INET_ECN_dontxmit(sk);
178 void tcp_init_congestion_control(struct sock *sk)
180 const struct inet_connection_sock *icsk = inet_csk(sk);
182 tcp_sk(sk)->prior_ssthresh = 0;
183 if (icsk->icsk_ca_ops->init)
184 icsk->icsk_ca_ops->init(sk);
185 if (tcp_ca_needs_ecn(sk))
188 INET_ECN_dontxmit(sk);
191 static void tcp_reinit_congestion_control(struct sock *sk,
192 const struct tcp_congestion_ops *ca)
194 struct inet_connection_sock *icsk = inet_csk(sk);
196 tcp_cleanup_congestion_control(sk);
197 icsk->icsk_ca_ops = ca;
198 icsk->icsk_ca_setsockopt = 1;
199 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
201 if (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
202 tcp_init_congestion_control(sk);
205 /* Manage refcounts on socket close. */
206 void tcp_cleanup_congestion_control(struct sock *sk)
208 struct inet_connection_sock *icsk = inet_csk(sk);
210 if (icsk->icsk_ca_ops->release)
211 icsk->icsk_ca_ops->release(sk);
212 module_put(icsk->icsk_ca_ops->owner);
215 /* Used by sysctl to change default congestion control */
216 int tcp_set_default_congestion_control(const char *name)
218 struct tcp_congestion_ops *ca;
221 spin_lock(&tcp_cong_list_lock);
222 ca = tcp_ca_find(name);
223 #ifdef CONFIG_MODULES
224 if (!ca && capable(CAP_NET_ADMIN)) {
225 spin_unlock(&tcp_cong_list_lock);
227 request_module("tcp_%s", name);
228 spin_lock(&tcp_cong_list_lock);
229 ca = tcp_ca_find(name);
234 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
235 list_move(&ca->list, &tcp_cong_list);
238 spin_unlock(&tcp_cong_list_lock);
243 /* Set default value from kernel configuration at bootup */
244 static int __init tcp_congestion_default(void)
246 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
248 late_initcall(tcp_congestion_default);
250 /* Build string with list of available congestion control values */
251 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
253 struct tcp_congestion_ops *ca;
257 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
258 offs += snprintf(buf + offs, maxlen - offs,
260 offs == 0 ? "" : " ", ca->name);
265 /* Get current default congestion control */
266 void tcp_get_default_congestion_control(char *name)
268 struct tcp_congestion_ops *ca;
269 /* We will always have reno... */
270 BUG_ON(list_empty(&tcp_cong_list));
273 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
274 strncpy(name, ca->name, TCP_CA_NAME_MAX);
278 /* Built list of non-restricted congestion control values */
279 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
281 struct tcp_congestion_ops *ca;
286 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
287 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
289 offs += snprintf(buf + offs, maxlen - offs,
291 offs == 0 ? "" : " ", ca->name);
296 /* Change list of non-restricted congestion control */
297 int tcp_set_allowed_congestion_control(char *val)
299 struct tcp_congestion_ops *ca;
300 char *saved_clone, *clone, *name;
303 saved_clone = clone = kstrdup(val, GFP_USER);
307 spin_lock(&tcp_cong_list_lock);
308 /* pass 1 check for bad entries */
309 while ((name = strsep(&clone, " ")) && *name) {
310 ca = tcp_ca_find(name);
317 /* pass 2 clear old values */
318 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
319 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
321 /* pass 3 mark as allowed */
322 while ((name = strsep(&val, " ")) && *name) {
323 ca = tcp_ca_find(name);
326 ca->flags |= TCP_CONG_NON_RESTRICTED;
329 spin_unlock(&tcp_cong_list_lock);
335 /* Change congestion control for socket */
336 int tcp_set_congestion_control(struct sock *sk, const char *name)
338 struct inet_connection_sock *icsk = inet_csk(sk);
339 const struct tcp_congestion_ops *ca;
342 if (icsk->icsk_ca_dst_locked)
346 ca = __tcp_ca_find_autoload(name);
347 /* No change asking for existing value */
348 if (ca == icsk->icsk_ca_ops) {
349 icsk->icsk_ca_setsockopt = 1;
354 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
355 ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
357 else if (!try_module_get(ca->owner))
360 tcp_reinit_congestion_control(sk, ca);
366 /* Slow start is used when congestion window is no greater than the slow start
367 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
368 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
369 * something better;) a packet is only considered (s)acked in its entirety to
370 * defend the ACK attacks described in the RFC. Slow start processes a stretch
371 * ACK of degree N as if N acks of degree 1 are received back to back except
372 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
373 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
375 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
377 u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
379 acked -= cwnd - tp->snd_cwnd;
380 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
384 EXPORT_SYMBOL_GPL(tcp_slow_start);
386 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
387 * for every packet that was ACKed.
389 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
391 /* If credits accumulated at a higher w, apply them gently now. */
392 if (tp->snd_cwnd_cnt >= w) {
393 tp->snd_cwnd_cnt = 0;
397 tp->snd_cwnd_cnt += acked;
398 if (tp->snd_cwnd_cnt >= w) {
399 u32 delta = tp->snd_cwnd_cnt / w;
401 tp->snd_cwnd_cnt -= delta * w;
402 tp->snd_cwnd += delta;
404 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
406 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
409 * TCP Reno congestion control
410 * This is special case used for fallback as well.
412 /* This is Jacobson's slow start and congestion avoidance.
413 * SIGCOMM '88, p. 328.
415 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
417 struct tcp_sock *tp = tcp_sk(sk);
419 if (!tcp_is_cwnd_limited(sk))
422 /* In "safe" area, increase. */
423 if (tcp_in_slow_start(tp)) {
424 acked = tcp_slow_start(tp, acked);
428 /* In dangerous area, increase slowly. */
429 tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
431 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
433 /* Slow start threshold is half the congestion window (min 2) */
434 u32 tcp_reno_ssthresh(struct sock *sk)
436 const struct tcp_sock *tp = tcp_sk(sk);
438 return max(tp->snd_cwnd >> 1U, 2U);
440 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
442 struct tcp_congestion_ops tcp_reno = {
443 .flags = TCP_CONG_NON_RESTRICTED,
445 .owner = THIS_MODULE,
446 .ssthresh = tcp_reno_ssthresh,
447 .cong_avoid = tcp_reno_cong_avoid,