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 #include <linux/module.h>
10 #include <linux/mm.h>
11 #include <linux/types.h>
12 #include <linux/list.h>
13 #include <net/tcp.h>
14
15 int sysctl_tcp_max_ssthresh = 0;
16
17 static DEFINE_SPINLOCK(tcp_cong_list_lock);
18 static LIST_HEAD(tcp_cong_list);
19
20 /* Simple linear search, don't expect many entries! */
21 static struct tcp_congestion_ops *tcp_ca_find(const char *name)
22 {
23 struct tcp_congestion_ops *e;
24
25 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
26 if (strcmp(e->name, name) == 0)
27 return e;
28 }
29
30 return NULL;
31 }
32
33 /*
34 * Attach new congestion control algorithm to the list
35 * of available options.
36 */
37 int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
38 {
39 int ret = 0;
40
41 /* all algorithms must implement ssthresh and cong_avoid ops */
42 if (!ca->ssthresh || !ca->cong_avoid) {
43 printk(KERN_ERR "TCP %s does not implement required ops\n",
44 ca->name);
45 return -EINVAL;
46 }
47
48 spin_lock(&tcp_cong_list_lock);
49 if (tcp_ca_find(ca->name)) {
50 printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
51 ret = -EEXIST;
52 } else {
53 list_add_tail_rcu(&ca->list, &tcp_cong_list);
54 printk(KERN_INFO "TCP %s registered\n", ca->name);
55 }
56 spin_unlock(&tcp_cong_list_lock);
57
58 return ret;
59 }
60 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
61
62 /*
63 * Remove congestion control algorithm, called from
64 * the module's remove function. Module ref counts are used
65 * to ensure that this can't be done till all sockets using
66 * that method are closed.
67 */
68 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
69 {
70 spin_lock(&tcp_cong_list_lock);
71 list_del_rcu(&ca->list);
72 spin_unlock(&tcp_cong_list_lock);
73 }
74 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
75
76 /* Assign choice of congestion control. */
77 void tcp_init_congestion_control(struct sock *sk)
78 {
79 struct inet_connection_sock *icsk = inet_csk(sk);
80 struct tcp_congestion_ops *ca;
81
82 /* if no choice made yet assign the current value set as default */
83 if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
84 rcu_read_lock();
85 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
86 if (try_module_get(ca->owner)) {
87 icsk->icsk_ca_ops = ca;
88 break;
89 }
90
91 /* fallback to next available */
92 }
93 rcu_read_unlock();
94 }
95
96 if (icsk->icsk_ca_ops->init)
97 icsk->icsk_ca_ops->init(sk);
98 }
99
100 /* Manage refcounts on socket close. */
101 void tcp_cleanup_congestion_control(struct sock *sk)
102 {
103 struct inet_connection_sock *icsk = inet_csk(sk);
104
105 if (icsk->icsk_ca_ops->release)
106 icsk->icsk_ca_ops->release(sk);
107 module_put(icsk->icsk_ca_ops->owner);
108 }
109
110 /* Used by sysctl to change default congestion control */
111 int tcp_set_default_congestion_control(const char *name)
112 {
113 struct tcp_congestion_ops *ca;
114 int ret = -ENOENT;
115
116 spin_lock(&tcp_cong_list_lock);
117 ca = tcp_ca_find(name);
118 #ifdef CONFIG_KMOD
119 if (!ca && capable(CAP_SYS_MODULE)) {
120 spin_unlock(&tcp_cong_list_lock);
121
122 request_module("tcp_%s", name);
123 spin_lock(&tcp_cong_list_lock);
124 ca = tcp_ca_find(name);
125 }
126 #endif
127
128 if (ca) {
129 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
130 list_move(&ca->list, &tcp_cong_list);
131 ret = 0;
132 }
133 spin_unlock(&tcp_cong_list_lock);
134
135 return ret;
136 }
137
138 /* Set default value from kernel configuration at bootup */
139 static int __init tcp_congestion_default(void)
140 {
141 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
142 }
143 late_initcall(tcp_congestion_default);
144
145
146 /* Build string with list of available congestion control values */
147 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
148 {
149 struct tcp_congestion_ops *ca;
150 size_t offs = 0;
151
152 rcu_read_lock();
153 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
154 offs += snprintf(buf + offs, maxlen - offs,
155 "%s%s",
156 offs == 0 ? "" : " ", ca->name);
157
158 }
159 rcu_read_unlock();
160 }
161
162 /* Get current default congestion control */
163 void tcp_get_default_congestion_control(char *name)
164 {
165 struct tcp_congestion_ops *ca;
166 /* We will always have reno... */
167 BUG_ON(list_empty(&tcp_cong_list));
168
169 rcu_read_lock();
170 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
171 strncpy(name, ca->name, TCP_CA_NAME_MAX);
172 rcu_read_unlock();
173 }
174
175 /* Built list of non-restricted congestion control values */
176 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
177 {
178 struct tcp_congestion_ops *ca;
179 size_t offs = 0;
180
181 *buf = '\0';
182 rcu_read_lock();
183 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
184 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
185 continue;
186 offs += snprintf(buf + offs, maxlen - offs,
187 "%s%s",
188 offs == 0 ? "" : " ", ca->name);
189
190 }
191 rcu_read_unlock();
192 }
193
194 /* Change list of non-restricted congestion control */
195 int tcp_set_allowed_congestion_control(char *val)
196 {
197 struct tcp_congestion_ops *ca;
198 char *clone, *name;
199 int ret = 0;
200
201 clone = kstrdup(val, GFP_USER);
202 if (!clone)
203 return -ENOMEM;
204
205 spin_lock(&tcp_cong_list_lock);
206 /* pass 1 check for bad entries */
207 while ((name = strsep(&clone, " ")) && *name) {
208 ca = tcp_ca_find(name);
209 if (!ca) {
210 ret = -ENOENT;
211 goto out;
212 }
213 }
214
215 /* pass 2 clear old values */
216 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
217 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
218
219 /* pass 3 mark as allowed */
220 while ((name = strsep(&val, " ")) && *name) {
221 ca = tcp_ca_find(name);
222 WARN_ON(!ca);
223 if (ca)
224 ca->flags |= TCP_CONG_NON_RESTRICTED;
225 }
226 out:
227 spin_unlock(&tcp_cong_list_lock);
228
229 return ret;
230 }
231
232
233 /* Change congestion control for socket */
234 int tcp_set_congestion_control(struct sock *sk, const char *name)
235 {
236 struct inet_connection_sock *icsk = inet_csk(sk);
237 struct tcp_congestion_ops *ca;
238 int err = 0;
239
240 rcu_read_lock();
241 ca = tcp_ca_find(name);
242
243 /* no change asking for existing value */
244 if (ca == icsk->icsk_ca_ops)
245 goto out;
246
247 #ifdef CONFIG_KMOD
248 /* not found attempt to autoload module */
249 if (!ca && capable(CAP_SYS_MODULE)) {
250 rcu_read_unlock();
251 request_module("tcp_%s", name);
252 rcu_read_lock();
253 ca = tcp_ca_find(name);
254 }
255 #endif
256 if (!ca)
257 err = -ENOENT;
258
259 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || capable(CAP_NET_ADMIN)))
260 err = -EPERM;
261
262 else if (!try_module_get(ca->owner))
263 err = -EBUSY;
264
265 else {
266 tcp_cleanup_congestion_control(sk);
267 icsk->icsk_ca_ops = ca;
268
269 if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
270 icsk->icsk_ca_ops->init(sk);
271 }
272 out:
273 rcu_read_unlock();
274 return err;
275 }
276
277 /* RFC2861 Check whether we are limited by application or congestion window
278 * This is the inverse of cwnd check in tcp_tso_should_defer
279 */
280 int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
281 {
282 const struct tcp_sock *tp = tcp_sk(sk);
283 u32 left;
284
285 if (in_flight >= tp->snd_cwnd)
286 return 1;
287
288 left = tp->snd_cwnd - in_flight;
289 if (sk_can_gso(sk) &&
290 left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
291 left * tp->mss_cache < 65536)
292 return 1;
293 return left <= tcp_max_burst(tp);
294 }
295 EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
296
297 /*
298 * Slow start is used when congestion window is less than slow start
299 * threshold. This version implements the basic RFC2581 version
300 * and optionally supports:
301 * RFC3742 Limited Slow Start - growth limited to max_ssthresh
302 * RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
303 */
304 void tcp_slow_start(struct tcp_sock *tp)
305 {
306 int cnt; /* increase in packets */
307
308 /* RFC3465: ABC Slow start
309 * Increase only after a full MSS of bytes is acked
310 *
311 * TCP sender SHOULD increase cwnd by the number of
312 * previously unacknowledged bytes ACKed by each incoming
313 * acknowledgment, provided the increase is not more than L
314 */
315 if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
316 return;
317
318 if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
319 cnt = sysctl_tcp_max_ssthresh >> 1; /* limited slow start */
320 else
321 cnt = tp->snd_cwnd; /* exponential increase */
322
323 /* RFC3465: ABC
324 * We MAY increase by 2 if discovered delayed ack
325 */
326 if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
327 cnt <<= 1;
328 tp->bytes_acked = 0;
329
330 tp->snd_cwnd_cnt += cnt;
331 while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
332 tp->snd_cwnd_cnt -= tp->snd_cwnd;
333 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
334 tp->snd_cwnd++;
335 }
336 }
337 EXPORT_SYMBOL_GPL(tcp_slow_start);
338
339 /*
340 * TCP Reno congestion control
341 * This is special case used for fallback as well.
342 */
343 /* This is Jacobson's slow start and congestion avoidance.
344 * SIGCOMM '88, p. 328.
345 */
346 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
347 {
348 struct tcp_sock *tp = tcp_sk(sk);
349
350 if (!tcp_is_cwnd_limited(sk, in_flight))
351 return;
352
353 /* In "safe" area, increase. */
354 if (tp->snd_cwnd <= tp->snd_ssthresh)
355 tcp_slow_start(tp);
356
357 /* In dangerous area, increase slowly. */
358 else if (sysctl_tcp_abc) {
359 /* RFC3465: Appropriate Byte Count
360 * increase once for each full cwnd acked
361 */
362 if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
363 tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
364 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
365 tp->snd_cwnd++;
366 }
367 } else {
368 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd */
369 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
370 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
371 tp->snd_cwnd++;
372 tp->snd_cwnd_cnt = 0;
373 } else
374 tp->snd_cwnd_cnt++;
375 }
376 }
377 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
378
379 /* Slow start threshold is half the congestion window (min 2) */
380 u32 tcp_reno_ssthresh(struct sock *sk)
381 {
382 const struct tcp_sock *tp = tcp_sk(sk);
383 return max(tp->snd_cwnd >> 1U, 2U);
384 }
385 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
386
387 /* Lower bound on congestion window with halving. */
388 u32 tcp_reno_min_cwnd(const struct sock *sk)
389 {
390 const struct tcp_sock *tp = tcp_sk(sk);
391 return tp->snd_ssthresh/2;
392 }
393 EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
394
395 struct tcp_congestion_ops tcp_reno = {
396 .flags = TCP_CONG_NON_RESTRICTED,
397 .name = "reno",
398 .owner = THIS_MODULE,
399 .ssthresh = tcp_reno_ssthresh,
400 .cong_avoid = tcp_reno_cong_avoid,
401 .min_cwnd = tcp_reno_min_cwnd,
402 };
403
404 /* Initial congestion control used (until SYN)
405 * really reno under another name so we can tell difference
406 * during tcp_set_default_congestion_control
407 */
408 struct tcp_congestion_ops tcp_init_congestion_ops = {
409 .name = "",
410 .owner = THIS_MODULE,
411 .ssthresh = tcp_reno_ssthresh,
412 .cong_avoid = tcp_reno_cong_avoid,
413 .min_cwnd = tcp_reno_min_cwnd,
414 };
415 EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);
416
|
This page was automatically generated by the
LXR engine.
|