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