Merge branch 'master'
[linux-2.6] / net / ipv4 / tcp_cong.c
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 static DEFINE_SPINLOCK(tcp_cong_list_lock);
16 static LIST_HEAD(tcp_cong_list);
17
18 /* Simple linear search, don't expect many entries! */
19 static struct tcp_congestion_ops *tcp_ca_find(const char *name)
20 {
21         struct tcp_congestion_ops *e;
22
23         list_for_each_entry_rcu(e, &tcp_cong_list, list) {
24                 if (strcmp(e->name, name) == 0)
25                         return e;
26         }
27
28         return NULL;
29 }
30
31 /*
32  * Attach new congestion control algorthim to the list
33  * of available options.
34  */
35 int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
36 {
37         int ret = 0;
38
39         /* all algorithms must implement ssthresh and cong_avoid ops */
40         if (!ca->ssthresh || !ca->cong_avoid) {
41                 printk(KERN_ERR "TCP %s does not implement required ops\n",
42                        ca->name);
43                 return -EINVAL;
44         }
45
46         spin_lock(&tcp_cong_list_lock);
47         if (tcp_ca_find(ca->name)) {
48                 printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
49                 ret = -EEXIST;
50         } else {
51                 list_add_rcu(&ca->list, &tcp_cong_list);
52                 printk(KERN_INFO "TCP %s registered\n", ca->name);
53         }
54         spin_unlock(&tcp_cong_list_lock);
55
56         return ret;
57 }
58 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
59
60 /*
61  * Remove congestion control algorithm, called from
62  * the module's remove function.  Module ref counts are used
63  * to ensure that this can't be done till all sockets using
64  * that method are closed.
65  */
66 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
67 {
68         spin_lock(&tcp_cong_list_lock);
69         list_del_rcu(&ca->list);
70         spin_unlock(&tcp_cong_list_lock);
71 }
72 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
73
74 /* Assign choice of congestion control. */
75 void tcp_init_congestion_control(struct sock *sk)
76 {
77         struct inet_connection_sock *icsk = inet_csk(sk);
78         struct tcp_congestion_ops *ca;
79
80         if (icsk->icsk_ca_ops != &tcp_init_congestion_ops)
81                 return;
82
83         rcu_read_lock();
84         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
85                 if (try_module_get(ca->owner)) {
86                         icsk->icsk_ca_ops = ca;
87                         break;
88                 }
89
90         }
91         rcu_read_unlock();
92
93         if (icsk->icsk_ca_ops->init)
94                 icsk->icsk_ca_ops->init(sk);
95 }
96
97 /* Manage refcounts on socket close. */
98 void tcp_cleanup_congestion_control(struct sock *sk)
99 {
100         struct inet_connection_sock *icsk = inet_csk(sk);
101
102         if (icsk->icsk_ca_ops->release)
103                 icsk->icsk_ca_ops->release(sk);
104         module_put(icsk->icsk_ca_ops->owner);
105 }
106
107 /* Used by sysctl to change default congestion control */
108 int tcp_set_default_congestion_control(const char *name)
109 {
110         struct tcp_congestion_ops *ca;
111         int ret = -ENOENT;
112
113         spin_lock(&tcp_cong_list_lock);
114         ca = tcp_ca_find(name);
115 #ifdef CONFIG_KMOD
116         if (!ca) {
117                 spin_unlock(&tcp_cong_list_lock);
118
119                 request_module("tcp_%s", name);
120                 spin_lock(&tcp_cong_list_lock);
121                 ca = tcp_ca_find(name);
122         }
123 #endif
124
125         if (ca) {
126                 list_move(&ca->list, &tcp_cong_list);
127                 ret = 0;
128         }
129         spin_unlock(&tcp_cong_list_lock);
130
131         return ret;
132 }
133
134 /* Get current default congestion control */
135 void tcp_get_default_congestion_control(char *name)
136 {
137         struct tcp_congestion_ops *ca;
138         /* We will always have reno... */
139         BUG_ON(list_empty(&tcp_cong_list));
140
141         rcu_read_lock();
142         ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
143         strncpy(name, ca->name, TCP_CA_NAME_MAX);
144         rcu_read_unlock();
145 }
146
147 /* Change congestion control for socket */
148 int tcp_set_congestion_control(struct sock *sk, const char *name)
149 {
150         struct inet_connection_sock *icsk = inet_csk(sk);
151         struct tcp_congestion_ops *ca;
152         int err = 0;
153
154         rcu_read_lock();
155         ca = tcp_ca_find(name);
156         if (ca == icsk->icsk_ca_ops)
157                 goto out;
158
159         if (!ca)
160                 err = -ENOENT;
161
162         else if (!try_module_get(ca->owner))
163                 err = -EBUSY;
164
165         else {
166                 tcp_cleanup_congestion_control(sk);
167                 icsk->icsk_ca_ops = ca;
168                 if (icsk->icsk_ca_ops->init)
169                         icsk->icsk_ca_ops->init(sk);
170         }
171  out:
172         rcu_read_unlock();
173         return err;
174 }
175
176
177 /*
178  * Linear increase during slow start
179  */
180 void tcp_slow_start(struct tcp_sock *tp)
181 {
182         if (sysctl_tcp_abc) {
183                 /* RFC3465: Slow Start
184                  * TCP sender SHOULD increase cwnd by the number of
185                  * previously unacknowledged bytes ACKed by each incoming
186                  * acknowledgment, provided the increase is not more than L
187                  */
188                 if (tp->bytes_acked < tp->mss_cache)
189                         return;
190
191                 /* We MAY increase by 2 if discovered delayed ack */
192                 if (sysctl_tcp_abc > 1 && tp->bytes_acked > 2*tp->mss_cache) {
193                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
194                                 tp->snd_cwnd++;
195                 }
196         }
197         tp->bytes_acked = 0;
198
199         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
200                 tp->snd_cwnd++;
201 }
202 EXPORT_SYMBOL_GPL(tcp_slow_start);
203
204 /*
205  * TCP Reno congestion control
206  * This is special case used for fallback as well.
207  */
208 /* This is Jacobson's slow start and congestion avoidance.
209  * SIGCOMM '88, p. 328.
210  */
211 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 rtt, u32 in_flight,
212                          int flag)
213 {
214         struct tcp_sock *tp = tcp_sk(sk);
215
216         if (!tcp_is_cwnd_limited(sk, in_flight))
217                 return;
218
219         /* In "safe" area, increase. */
220         if (tp->snd_cwnd <= tp->snd_ssthresh)
221                 tcp_slow_start(tp);
222
223         /* In dangerous area, increase slowly. */
224         else if (sysctl_tcp_abc) {
225                 /* RFC3465: Appropriate Byte Count
226                  * increase once for each full cwnd acked
227                  */
228                 if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
229                         tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
230                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
231                                 tp->snd_cwnd++;
232                 }
233         } else {
234                 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd */
235                 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
236                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
237                                 tp->snd_cwnd++;
238                         tp->snd_cwnd_cnt = 0;
239                 } else
240                         tp->snd_cwnd_cnt++;
241         }
242 }
243 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
244
245 /* Slow start threshold is half the congestion window (min 2) */
246 u32 tcp_reno_ssthresh(struct sock *sk)
247 {
248         const struct tcp_sock *tp = tcp_sk(sk);
249         return max(tp->snd_cwnd >> 1U, 2U);
250 }
251 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
252
253 /* Lower bound on congestion window with halving. */
254 u32 tcp_reno_min_cwnd(const struct sock *sk)
255 {
256         const struct tcp_sock *tp = tcp_sk(sk);
257         return tp->snd_ssthresh/2;
258 }
259 EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
260
261 struct tcp_congestion_ops tcp_reno = {
262         .name           = "reno",
263         .owner          = THIS_MODULE,
264         .ssthresh       = tcp_reno_ssthresh,
265         .cong_avoid     = tcp_reno_cong_avoid,
266         .min_cwnd       = tcp_reno_min_cwnd,
267 };
268
269 /* Initial congestion control used (until SYN)
270  * really reno under another name so we can tell difference
271  * during tcp_set_default_congestion_control
272  */
273 struct tcp_congestion_ops tcp_init_congestion_ops  = {
274         .name           = "",
275         .owner          = THIS_MODULE,
276         .ssthresh       = tcp_reno_ssthresh,
277         .cong_avoid     = tcp_reno_cong_avoid,
278         .min_cwnd       = tcp_reno_min_cwnd,
279 };
280 EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);