1 // SPDX-License-Identifier: GPL-2.0-only
3 * Pluggable TCP congestion control support and newReno
5 * Based on ideas from I/O scheduler support and Web100.
7 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
10 #define pr_fmt(fmt) "TCP: " fmt
12 #include <linux/module.h>
14 #include <linux/types.h>
15 #include <linux/list.h>
16 #include <linux/gfp.h>
17 #include <linux/jhash.h>
20 static DEFINE_SPINLOCK(tcp_cong_list_lock);
21 static LIST_HEAD(tcp_cong_list);
23 /* Simple linear search, don't expect many entries! */
24 static struct tcp_congestion_ops *tcp_ca_find(const char *name)
26 struct tcp_congestion_ops *e;
28 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
29 if (strcmp(e->name, name) == 0)
36 /* Must be called with rcu lock held */
37 static struct tcp_congestion_ops *tcp_ca_find_autoload(struct net *net,
40 struct tcp_congestion_ops *ca = tcp_ca_find(name);
43 if (!ca && capable(CAP_NET_ADMIN)) {
45 request_module("tcp_%s", name);
47 ca = tcp_ca_find(name);
53 /* Simple linear search, not much in here. */
54 struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
56 struct tcp_congestion_ops *e;
58 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
67 * Attach new congestion control algorithm to the list
68 * of available options.
70 int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
74 /* all algorithms must implement these */
75 if (!ca->ssthresh || !ca->undo_cwnd ||
76 !(ca->cong_avoid || ca->cong_control)) {
77 pr_err("%s does not implement required ops\n", ca->name);
81 ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
83 spin_lock(&tcp_cong_list_lock);
84 if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
85 pr_notice("%s already registered or non-unique key\n",
89 list_add_tail_rcu(&ca->list, &tcp_cong_list);
90 pr_debug("%s registered\n", ca->name);
92 spin_unlock(&tcp_cong_list_lock);
96 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
99 * Remove congestion control algorithm, called from
100 * the module's remove function. Module ref counts are used
101 * to ensure that this can't be done till all sockets using
102 * that method are closed.
104 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
106 spin_lock(&tcp_cong_list_lock);
107 list_del_rcu(&ca->list);
108 spin_unlock(&tcp_cong_list_lock);
110 /* Wait for outstanding readers to complete before the
111 * module gets removed entirely.
113 * A try_module_get() should fail by now as our module is
114 * in "going" state since no refs are held anymore and
115 * module_exit() handler being called.
119 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
121 u32 tcp_ca_get_key_by_name(struct net *net, const char *name, bool *ecn_ca)
123 const struct tcp_congestion_ops *ca;
124 u32 key = TCP_CA_UNSPEC;
129 ca = tcp_ca_find_autoload(net, name);
132 *ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
138 EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
140 char *tcp_ca_get_name_by_key(u32 key, char *buffer)
142 const struct tcp_congestion_ops *ca;
146 ca = tcp_ca_find_key(key);
148 ret = strncpy(buffer, ca->name,
154 EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
156 /* Assign choice of congestion control. */
157 void tcp_assign_congestion_control(struct sock *sk)
159 struct net *net = sock_net(sk);
160 struct inet_connection_sock *icsk = inet_csk(sk);
161 const struct tcp_congestion_ops *ca;
164 ca = rcu_dereference(net->ipv4.tcp_congestion_control);
165 if (unlikely(!try_module_get(ca->owner)))
167 icsk->icsk_ca_ops = ca;
170 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
171 if (ca->flags & TCP_CONG_NEEDS_ECN)
174 INET_ECN_dontxmit(sk);
177 void tcp_init_congestion_control(struct sock *sk)
179 const struct inet_connection_sock *icsk = inet_csk(sk);
181 tcp_sk(sk)->prior_ssthresh = 0;
182 if (icsk->icsk_ca_ops->init)
183 icsk->icsk_ca_ops->init(sk);
184 if (tcp_ca_needs_ecn(sk))
187 INET_ECN_dontxmit(sk);
190 static void tcp_reinit_congestion_control(struct sock *sk,
191 const struct tcp_congestion_ops *ca)
193 struct inet_connection_sock *icsk = inet_csk(sk);
195 tcp_cleanup_congestion_control(sk);
196 icsk->icsk_ca_ops = ca;
197 icsk->icsk_ca_setsockopt = 1;
198 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
200 if (ca->flags & TCP_CONG_NEEDS_ECN)
203 INET_ECN_dontxmit(sk);
205 if (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
206 tcp_init_congestion_control(sk);
209 /* Manage refcounts on socket close. */
210 void tcp_cleanup_congestion_control(struct sock *sk)
212 struct inet_connection_sock *icsk = inet_csk(sk);
214 if (icsk->icsk_ca_ops->release)
215 icsk->icsk_ca_ops->release(sk);
216 module_put(icsk->icsk_ca_ops->owner);
219 /* Used by sysctl to change default congestion control */
220 int tcp_set_default_congestion_control(struct net *net, const char *name)
222 struct tcp_congestion_ops *ca;
223 const struct tcp_congestion_ops *prev;
227 ca = tcp_ca_find_autoload(net, name);
230 } else if (!try_module_get(ca->owner)) {
232 } else if (!net_eq(net, &init_net) &&
233 !(ca->flags & TCP_CONG_NON_RESTRICTED)) {
234 /* Only init netns can set default to a restricted algorithm */
237 prev = xchg(&net->ipv4.tcp_congestion_control, ca);
239 module_put(prev->owner);
241 ca->flags |= TCP_CONG_NON_RESTRICTED;
249 /* Set default value from kernel configuration at bootup */
250 static int __init tcp_congestion_default(void)
252 return tcp_set_default_congestion_control(&init_net,
253 CONFIG_DEFAULT_TCP_CONG);
255 late_initcall(tcp_congestion_default);
257 /* Build string with list of available congestion control values */
258 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
260 struct tcp_congestion_ops *ca;
264 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
265 offs += snprintf(buf + offs, maxlen - offs,
267 offs == 0 ? "" : " ", ca->name);
272 /* Get current default congestion control */
273 void tcp_get_default_congestion_control(struct net *net, char *name)
275 const struct tcp_congestion_ops *ca;
278 ca = rcu_dereference(net->ipv4.tcp_congestion_control);
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. If load is false, then it is the
341 * responsibility of the caller to call tcp_init_congestion_control or
342 * tcp_reinit_congestion_control (if the current congestion control was
343 * already initialized.
345 int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
346 bool reinit, bool cap_net_admin)
348 struct inet_connection_sock *icsk = inet_csk(sk);
349 const struct tcp_congestion_ops *ca;
352 if (icsk->icsk_ca_dst_locked)
357 ca = tcp_ca_find(name);
359 ca = tcp_ca_find_autoload(sock_net(sk), name);
361 /* No change asking for existing value */
362 if (ca == icsk->icsk_ca_ops) {
363 icsk->icsk_ca_setsockopt = 1;
370 const struct tcp_congestion_ops *old_ca = icsk->icsk_ca_ops;
372 if (try_module_get(ca->owner)) {
374 tcp_reinit_congestion_control(sk, ca);
376 icsk->icsk_ca_ops = ca;
377 module_put(old_ca->owner);
382 } else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || cap_net_admin)) {
384 } else if (!try_module_get(ca->owner)) {
387 tcp_reinit_congestion_control(sk, ca);
394 /* Slow start is used when congestion window is no greater than the slow start
395 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
396 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
397 * something better;) a packet is only considered (s)acked in its entirety to
398 * defend the ACK attacks described in the RFC. Slow start processes a stretch
399 * ACK of degree N as if N acks of degree 1 are received back to back except
400 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
401 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
403 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
405 u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
407 acked -= cwnd - tp->snd_cwnd;
408 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
412 EXPORT_SYMBOL_GPL(tcp_slow_start);
414 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
415 * for every packet that was ACKed.
417 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
419 /* If credits accumulated at a higher w, apply them gently now. */
420 if (tp->snd_cwnd_cnt >= w) {
421 tp->snd_cwnd_cnt = 0;
425 tp->snd_cwnd_cnt += acked;
426 if (tp->snd_cwnd_cnt >= w) {
427 u32 delta = tp->snd_cwnd_cnt / w;
429 tp->snd_cwnd_cnt -= delta * w;
430 tp->snd_cwnd += delta;
432 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
434 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
437 * TCP Reno congestion control
438 * This is special case used for fallback as well.
440 /* This is Jacobson's slow start and congestion avoidance.
441 * SIGCOMM '88, p. 328.
443 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
445 struct tcp_sock *tp = tcp_sk(sk);
447 if (!tcp_is_cwnd_limited(sk))
450 /* In "safe" area, increase. */
451 if (tcp_in_slow_start(tp)) {
452 acked = tcp_slow_start(tp, acked);
456 /* In dangerous area, increase slowly. */
457 tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
459 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
461 /* Slow start threshold is half the congestion window (min 2) */
462 u32 tcp_reno_ssthresh(struct sock *sk)
464 const struct tcp_sock *tp = tcp_sk(sk);
466 return max(tp->snd_cwnd >> 1U, 2U);
468 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
470 u32 tcp_reno_undo_cwnd(struct sock *sk)
472 const struct tcp_sock *tp = tcp_sk(sk);
474 return max(tp->snd_cwnd, tp->prior_cwnd);
476 EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
478 struct tcp_congestion_ops tcp_reno = {
479 .flags = TCP_CONG_NON_RESTRICTED,
481 .owner = THIS_MODULE,
482 .ssthresh = tcp_reno_ssthresh,
483 .cong_avoid = tcp_reno_cong_avoid,
484 .undo_cwnd = tcp_reno_undo_cwnd,