1 /*
2 * Plugable TCP congestion control support and newReno
3 * congestion control.
4 * Based on ideas from I/O scheduler suport and Web100.
5 *
6 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
7 */
8
9 #define pr_fmt(fmt) "TCP: " fmt
10
11 #include <linux/module.h>
12 #include <linux/mm.h>
13 #include <linux/types.h>
14 #include <linux/list.h>
15 #include <linux/gfp.h>
16 #include <net/tcp.h>
17
18 int sysctl_tcp_max_ssthresh = 0;
19
20 static DEFINE_SPINLOCK(tcp_cong_list_lock);
21 static LIST_HEAD(tcp_cong_list);
22
23 /* Simple linear search, don't expect many entries! */
tcp_ca_find(const char * name)24 static struct tcp_congestion_ops *tcp_ca_find(const char *name)
25 {
26 struct tcp_congestion_ops *e;
27
28 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
29 if (strcmp(e->name, name) == 0)
30 return e;
31 }
32
33 return NULL;
34 }
35
36 /*
37 * Attach new congestion control algorithm to the list
38 * of available options.
39 */
tcp_register_congestion_control(struct tcp_congestion_ops * ca)40 int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
41 {
42 int ret = 0;
43
44 /* all algorithms must implement ssthresh and cong_avoid ops */
45 if (!ca->ssthresh || !ca->cong_avoid) {
46 pr_err("%s does not implement required ops\n", ca->name);
47 return -EINVAL;
48 }
49
50 spin_lock(&tcp_cong_list_lock);
51 if (tcp_ca_find(ca->name)) {
52 pr_notice("%s already registered\n", ca->name);
53 ret = -EEXIST;
54 } else {
55 list_add_tail_rcu(&ca->list, &tcp_cong_list);
56 pr_info("%s registered\n", ca->name);
57 }
58 spin_unlock(&tcp_cong_list_lock);
59
60 return ret;
61 }
62 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
63
64 /*
65 * Remove congestion control algorithm, called from
66 * the module's remove function. Module ref counts are used
67 * to ensure that this can't be done till all sockets using
68 * that method are closed.
69 */
tcp_unregister_congestion_control(struct tcp_congestion_ops * ca)70 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
71 {
72 spin_lock(&tcp_cong_list_lock);
73 list_del_rcu(&ca->list);
74 spin_unlock(&tcp_cong_list_lock);
75 }
76 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
77
78 /* Assign choice of congestion control. */
tcp_init_congestion_control(struct sock * sk)79 void tcp_init_congestion_control(struct sock *sk)
80 {
81 struct inet_connection_sock *icsk = inet_csk(sk);
82 struct tcp_congestion_ops *ca;
83
84 /* if no choice made yet assign the current value set as default */
85 if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
86 rcu_read_lock();
87 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
88 if (try_module_get(ca->owner)) {
89 icsk->icsk_ca_ops = ca;
90 break;
91 }
92
93 /* fallback to next available */
94 }
95 rcu_read_unlock();
96 }
97
98 if (icsk->icsk_ca_ops->init)
99 icsk->icsk_ca_ops->init(sk);
100 }
101
102 /* Manage refcounts on socket close. */
tcp_cleanup_congestion_control(struct sock * sk)103 void tcp_cleanup_congestion_control(struct sock *sk)
104 {
105 struct inet_connection_sock *icsk = inet_csk(sk);
106
107 if (icsk->icsk_ca_ops->release)
108 icsk->icsk_ca_ops->release(sk);
109 module_put(icsk->icsk_ca_ops->owner);
110 }
111
112 /* Used by sysctl to change default congestion control */
tcp_set_default_congestion_control(const char * name)113 int tcp_set_default_congestion_control(const char *name)
114 {
115 struct tcp_congestion_ops *ca;
116 int ret = -ENOENT;
117
118 spin_lock(&tcp_cong_list_lock);
119 ca = tcp_ca_find(name);
120 #ifdef CONFIG_MODULES
121 if (!ca && capable(CAP_NET_ADMIN)) {
122 spin_unlock(&tcp_cong_list_lock);
123
124 request_module("tcp_%s", name);
125 spin_lock(&tcp_cong_list_lock);
126 ca = tcp_ca_find(name);
127 }
128 #endif
129
130 if (ca) {
131 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
132 list_move(&ca->list, &tcp_cong_list);
133 ret = 0;
134 }
135 spin_unlock(&tcp_cong_list_lock);
136
137 return ret;
138 }
139
140 /* Set default value from kernel configuration at bootup */
tcp_congestion_default(void)141 static int __init tcp_congestion_default(void)
142 {
143 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
144 }
145 late_initcall(tcp_congestion_default);
146
147
148 /* Build string with list of available congestion control values */
tcp_get_available_congestion_control(char * buf,size_t maxlen)149 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
150 {
151 struct tcp_congestion_ops *ca;
152 size_t offs = 0;
153
154 rcu_read_lock();
155 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
156 offs += snprintf(buf + offs, maxlen - offs,
157 "%s%s",
158 offs == 0 ? "" : " ", ca->name);
159
160 }
161 rcu_read_unlock();
162 }
163
164 /* Get current default congestion control */
tcp_get_default_congestion_control(char * name)165 void tcp_get_default_congestion_control(char *name)
166 {
167 struct tcp_congestion_ops *ca;
168 /* We will always have reno... */
169 BUG_ON(list_empty(&tcp_cong_list));
170
171 rcu_read_lock();
172 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
173 strncpy(name, ca->name, TCP_CA_NAME_MAX);
174 rcu_read_unlock();
175 }
176
177 /* Built list of non-restricted congestion control values */
tcp_get_allowed_congestion_control(char * buf,size_t maxlen)178 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
179 {
180 struct tcp_congestion_ops *ca;
181 size_t offs = 0;
182
183 *buf = '\0';
184 rcu_read_lock();
185 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
186 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
187 continue;
188 offs += snprintf(buf + offs, maxlen - offs,
189 "%s%s",
190 offs == 0 ? "" : " ", ca->name);
191
192 }
193 rcu_read_unlock();
194 }
195
196 /* Change list of non-restricted congestion control */
tcp_set_allowed_congestion_control(char * val)197 int tcp_set_allowed_congestion_control(char *val)
198 {
199 struct tcp_congestion_ops *ca;
200 char *saved_clone, *clone, *name;
201 int ret = 0;
202
203 saved_clone = clone = kstrdup(val, GFP_USER);
204 if (!clone)
205 return -ENOMEM;
206
207 spin_lock(&tcp_cong_list_lock);
208 /* pass 1 check for bad entries */
209 while ((name = strsep(&clone, " ")) && *name) {
210 ca = tcp_ca_find(name);
211 if (!ca) {
212 ret = -ENOENT;
213 goto out;
214 }
215 }
216
217 /* pass 2 clear old values */
218 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
219 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
220
221 /* pass 3 mark as allowed */
222 while ((name = strsep(&val, " ")) && *name) {
223 ca = tcp_ca_find(name);
224 WARN_ON(!ca);
225 if (ca)
226 ca->flags |= TCP_CONG_NON_RESTRICTED;
227 }
228 out:
229 spin_unlock(&tcp_cong_list_lock);
230 kfree(saved_clone);
231
232 return ret;
233 }
234
235
236 /* Change congestion control for socket */
tcp_set_congestion_control(struct sock * sk,const char * name)237 int tcp_set_congestion_control(struct sock *sk, const char *name)
238 {
239 struct inet_connection_sock *icsk = inet_csk(sk);
240 struct tcp_congestion_ops *ca;
241 int err = 0;
242
243 rcu_read_lock();
244 ca = tcp_ca_find(name);
245
246 /* no change asking for existing value */
247 if (ca == icsk->icsk_ca_ops)
248 goto out;
249
250 #ifdef CONFIG_MODULES
251 /* not found attempt to autoload module */
252 if (!ca && capable(CAP_NET_ADMIN)) {
253 rcu_read_unlock();
254 request_module("tcp_%s", name);
255 rcu_read_lock();
256 ca = tcp_ca_find(name);
257 }
258 #endif
259 if (!ca)
260 err = -ENOENT;
261
262 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || capable(CAP_NET_ADMIN)))
263 err = -EPERM;
264
265 else if (!try_module_get(ca->owner))
266 err = -EBUSY;
267
268 else {
269 tcp_cleanup_congestion_control(sk);
270 icsk->icsk_ca_ops = ca;
271
272 if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
273 icsk->icsk_ca_ops->init(sk);
274 }
275 out:
276 rcu_read_unlock();
277 return err;
278 }
279
280 /* RFC2861 Check whether we are limited by application or congestion window
281 * This is the inverse of cwnd check in tcp_tso_should_defer
282 */
tcp_is_cwnd_limited(const struct sock * sk,u32 in_flight)283 int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
284 {
285 const struct tcp_sock *tp = tcp_sk(sk);
286 u32 left;
287
288 if (in_flight >= tp->snd_cwnd)
289 return 1;
290
291 left = tp->snd_cwnd - in_flight;
292 if (sk_can_gso(sk) &&
293 left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
294 left * tp->mss_cache < sk->sk_gso_max_size &&
295 left < sk->sk_gso_max_segs)
296 return 1;
297 return left <= tcp_max_tso_deferred_mss(tp);
298 }
299 EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
300
301 /*
302 * Slow start is used when congestion window is less than slow start
303 * threshold. This version implements the basic RFC2581 version
304 * and optionally supports:
305 * RFC3742 Limited Slow Start - growth limited to max_ssthresh
306 * RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
307 */
tcp_slow_start(struct tcp_sock * tp)308 void tcp_slow_start(struct tcp_sock *tp)
309 {
310 int cnt; /* increase in packets */
311
312 /* RFC3465: ABC Slow start
313 * Increase only after a full MSS of bytes is acked
314 *
315 * TCP sender SHOULD increase cwnd by the number of
316 * previously unacknowledged bytes ACKed by each incoming
317 * acknowledgment, provided the increase is not more than L
318 */
319 if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
320 return;
321
322 if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
323 cnt = sysctl_tcp_max_ssthresh >> 1; /* limited slow start */
324 else
325 cnt = tp->snd_cwnd; /* exponential increase */
326
327 /* RFC3465: ABC
328 * We MAY increase by 2 if discovered delayed ack
329 */
330 if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
331 cnt <<= 1;
332 tp->bytes_acked = 0;
333
334 tp->snd_cwnd_cnt += cnt;
335 while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
336 tp->snd_cwnd_cnt -= tp->snd_cwnd;
337 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
338 tp->snd_cwnd++;
339 }
340 }
341 EXPORT_SYMBOL_GPL(tcp_slow_start);
342
343 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
tcp_cong_avoid_ai(struct tcp_sock * tp,u32 w)344 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
345 {
346 if (tp->snd_cwnd_cnt >= w) {
347 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
348 tp->snd_cwnd++;
349 tp->snd_cwnd_cnt = 0;
350 } else {
351 tp->snd_cwnd_cnt++;
352 }
353 }
354 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
355
356 /*
357 * TCP Reno congestion control
358 * This is special case used for fallback as well.
359 */
360 /* This is Jacobson's slow start and congestion avoidance.
361 * SIGCOMM '88, p. 328.
362 */
tcp_reno_cong_avoid(struct sock * sk,u32 ack,u32 in_flight)363 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
364 {
365 struct tcp_sock *tp = tcp_sk(sk);
366
367 if (!tcp_is_cwnd_limited(sk, in_flight))
368 return;
369
370 /* In "safe" area, increase. */
371 if (tp->snd_cwnd <= tp->snd_ssthresh)
372 tcp_slow_start(tp);
373
374 /* In dangerous area, increase slowly. */
375 else if (sysctl_tcp_abc) {
376 /* RFC3465: Appropriate Byte Count
377 * increase once for each full cwnd acked
378 */
379 if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
380 tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
381 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
382 tp->snd_cwnd++;
383 }
384 } else {
385 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
386 }
387 }
388 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
389
390 /* Slow start threshold is half the congestion window (min 2) */
tcp_reno_ssthresh(struct sock * sk)391 u32 tcp_reno_ssthresh(struct sock *sk)
392 {
393 const struct tcp_sock *tp = tcp_sk(sk);
394 return max(tp->snd_cwnd >> 1U, 2U);
395 }
396 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
397
398 /* Lower bound on congestion window with halving. */
tcp_reno_min_cwnd(const struct sock * sk)399 u32 tcp_reno_min_cwnd(const struct sock *sk)
400 {
401 const struct tcp_sock *tp = tcp_sk(sk);
402 return tp->snd_ssthresh/2;
403 }
404 EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
405
406 struct tcp_congestion_ops tcp_reno = {
407 .flags = TCP_CONG_NON_RESTRICTED,
408 .name = "reno",
409 .owner = THIS_MODULE,
410 .ssthresh = tcp_reno_ssthresh,
411 .cong_avoid = tcp_reno_cong_avoid,
412 .min_cwnd = tcp_reno_min_cwnd,
413 };
414
415 /* Initial congestion control used (until SYN)
416 * really reno under another name so we can tell difference
417 * during tcp_set_default_congestion_control
418 */
419 struct tcp_congestion_ops tcp_init_congestion_ops = {
420 .name = "",
421 .owner = THIS_MODULE,
422 .ssthresh = tcp_reno_ssthresh,
423 .cong_avoid = tcp_reno_cong_avoid,
424 .min_cwnd = tcp_reno_min_cwnd,
425 };
426 EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);
427