1 /* Tom Kelly's Scalable TCP
2 *
3 * See htt://www-lce.eng.cam.ac.uk/~ctk21/scalable/
4 *
5 * John Heffner <jheffner@sc.edu>
6 */
7
8 #include <linux/module.h>
9 #include <net/tcp.h>
10
11 /* These factors derived from the recommended values in the aer:
12 * .01 and and 7/8. We use 50 instead of 100 to account for
13 * delayed ack.
14 */
15 #define TCP_SCALABLE_AI_CNT 50U
16 #define TCP_SCALABLE_MD_SCALE 3
17
18 static void tcp_scalable_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
19 {
20 struct tcp_sock *tp = tcp_sk(sk);
21
22 if (!tcp_is_cwnd_limited(sk, in_flight))
23 return;
24
25 if (tp->snd_cwnd <= tp->snd_ssthresh)
26 tcp_slow_start(tp);
27 else {
28 tp->snd_cwnd_cnt++;
29 if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){
30 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
31 tp->snd_cwnd++;
32 tp->snd_cwnd_cnt = 0;
33 }
34 }
35 }
36
37 static u32 tcp_scalable_ssthresh(struct sock *sk)
38 {
39 const struct tcp_sock *tp = tcp_sk(sk);
40 return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);
41 }
42
43
44 static struct tcp_congestion_ops tcp_scalable = {
45 .ssthresh = tcp_scalable_ssthresh,
46 .cong_avoid = tcp_scalable_cong_avoid,
47 .min_cwnd = tcp_reno_min_cwnd,
48
49 .owner = THIS_MODULE,
50 .name = "scalable",
51 };
52
53 static int __init tcp_scalable_register(void)
54 {
55 return tcp_register_congestion_control(&tcp_scalable);
56 }
57
58 static void __exit tcp_scalable_unregister(void)
59 {
60 tcp_unregister_congestion_control(&tcp_scalable);
61 }
62
63 module_init(tcp_scalable_register);
64 module_exit(tcp_scalable_unregister);
65
66 MODULE_AUTHOR("John Heffner");
67 MODULE_LICENSE("GPL");
68 MODULE_DESCRIPTION("Scalable TCP");
69
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