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.
172 /* Clear out private data before diag gets it and
173 * the ca has not been initialized.
176 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
177 if (ca->flags & TCP_CONG_NEEDS_ECN)
180 INET_ECN_dontxmit(sk);
183 void tcp_init_congestion_control(struct sock *sk)
185 const struct inet_connection_sock *icsk = inet_csk(sk);
187 if (icsk->icsk_ca_ops->init)
188 icsk->icsk_ca_ops->init(sk);
189 if (tcp_ca_needs_ecn(sk))
192 INET_ECN_dontxmit(sk);
195 static void tcp_reinit_congestion_control(struct sock *sk,
196 const struct tcp_congestion_ops *ca)
198 struct inet_connection_sock *icsk = inet_csk(sk);
200 tcp_cleanup_congestion_control(sk);
201 icsk->icsk_ca_ops = ca;
202 icsk->icsk_ca_setsockopt = 1;
204 if (sk->sk_state != TCP_CLOSE) {
205 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
206 tcp_init_congestion_control(sk);
210 /* Manage refcounts on socket close. */
211 void tcp_cleanup_congestion_control(struct sock *sk)
213 struct inet_connection_sock *icsk = inet_csk(sk);
215 if (icsk->icsk_ca_ops->release)
216 icsk->icsk_ca_ops->release(sk);
217 module_put(icsk->icsk_ca_ops->owner);
220 /* Used by sysctl to change default congestion control */
221 int tcp_set_default_congestion_control(const char *name)
223 struct tcp_congestion_ops *ca;
226 spin_lock(&tcp_cong_list_lock);
227 ca = tcp_ca_find(name);
228 #ifdef CONFIG_MODULES
229 if (!ca && capable(CAP_NET_ADMIN)) {
230 spin_unlock(&tcp_cong_list_lock);
232 request_module("tcp_%s", name);
233 spin_lock(&tcp_cong_list_lock);
234 ca = tcp_ca_find(name);
239 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
240 list_move(&ca->list, &tcp_cong_list);
243 spin_unlock(&tcp_cong_list_lock);
248 /* Set default value from kernel configuration at bootup */
249 static int __init tcp_congestion_default(void)
251 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
253 late_initcall(tcp_congestion_default);
255 /* Build string with list of available congestion control values */
256 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
258 struct tcp_congestion_ops *ca;
262 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
263 offs += snprintf(buf + offs, maxlen - offs,
265 offs == 0 ? "" : " ", ca->name);
270 /* Get current default congestion control */
271 void tcp_get_default_congestion_control(char *name)
273 struct tcp_congestion_ops *ca;
274 /* We will always have reno... */
275 BUG_ON(list_empty(&tcp_cong_list));
278 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
279 strncpy(name, ca->name, TCP_CA_NAME_MAX);
283 /* Built list of non-restricted congestion control values */
284 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
286 struct tcp_congestion_ops *ca;
291 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
292 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
294 offs += snprintf(buf + offs, maxlen - offs,
296 offs == 0 ? "" : " ", ca->name);
301 /* Change list of non-restricted congestion control */
302 int tcp_set_allowed_congestion_control(char *val)
304 struct tcp_congestion_ops *ca;
305 char *saved_clone, *clone, *name;
308 saved_clone = clone = kstrdup(val, GFP_USER);
312 spin_lock(&tcp_cong_list_lock);
313 /* pass 1 check for bad entries */
314 while ((name = strsep(&clone, " ")) && *name) {
315 ca = tcp_ca_find(name);
322 /* pass 2 clear old values */
323 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
324 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
326 /* pass 3 mark as allowed */
327 while ((name = strsep(&val, " ")) && *name) {
328 ca = tcp_ca_find(name);
331 ca->flags |= TCP_CONG_NON_RESTRICTED;
334 spin_unlock(&tcp_cong_list_lock);
340 /* Change congestion control for socket */
341 int tcp_set_congestion_control(struct sock *sk, const char *name)
343 struct inet_connection_sock *icsk = inet_csk(sk);
344 const struct tcp_congestion_ops *ca;
347 if (icsk->icsk_ca_dst_locked)
351 ca = __tcp_ca_find_autoload(name);
352 /* No change asking for existing value */
353 if (ca == icsk->icsk_ca_ops) {
354 icsk->icsk_ca_setsockopt = 1;
359 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
360 ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
362 else if (!try_module_get(ca->owner))
365 tcp_reinit_congestion_control(sk, ca);
371 /* Slow start is used when congestion window is no greater than the slow start
372 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
373 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
374 * something better;) a packet is only considered (s)acked in its entirety to
375 * defend the ACK attacks described in the RFC. Slow start processes a stretch
376 * ACK of degree N as if N acks of degree 1 are received back to back except
377 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
378 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
380 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
382 u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
384 acked -= cwnd - tp->snd_cwnd;
385 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
389 EXPORT_SYMBOL_GPL(tcp_slow_start);
391 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
392 * for every packet that was ACKed.
394 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
396 /* If credits accumulated at a higher w, apply them gently now. */
397 if (tp->snd_cwnd_cnt >= w) {
398 tp->snd_cwnd_cnt = 0;
402 tp->snd_cwnd_cnt += acked;
403 if (tp->snd_cwnd_cnt >= w) {
404 u32 delta = tp->snd_cwnd_cnt / w;
406 tp->snd_cwnd_cnt -= delta * w;
407 tp->snd_cwnd += delta;
409 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
411 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
414 * TCP Reno congestion control
415 * This is special case used for fallback as well.
417 /* This is Jacobson's slow start and congestion avoidance.
418 * SIGCOMM '88, p. 328.
420 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
422 struct tcp_sock *tp = tcp_sk(sk);
424 if (!tcp_is_cwnd_limited(sk))
427 /* In "safe" area, increase. */
428 if (tcp_in_slow_start(tp)) {
429 acked = tcp_slow_start(tp, acked);
433 /* In dangerous area, increase slowly. */
434 tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
436 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
438 /* Slow start threshold is half the congestion window (min 2) */
439 u32 tcp_reno_ssthresh(struct sock *sk)
441 const struct tcp_sock *tp = tcp_sk(sk);
443 return max(tp->snd_cwnd >> 1U, 2U);
445 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
447 u32 tcp_reno_undo_cwnd(struct sock *sk)
449 const struct tcp_sock *tp = tcp_sk(sk);
451 return max(tp->snd_cwnd, tp->snd_ssthresh << 1);
453 EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
455 struct tcp_congestion_ops tcp_reno = {
456 .flags = TCP_CONG_NON_RESTRICTED,
458 .owner = THIS_MODULE,
459 .ssthresh = tcp_reno_ssthresh,
460 .cong_avoid = tcp_reno_cong_avoid,
461 .undo_cwnd = tcp_reno_undo_cwnd,