xref: /linux/net/ipv4/tcp_scalable.c (revision 3932b9ca55b0be314a36d3e84faff3e823c081f5)
1 /* Tom Kelly's Scalable TCP
2  *
3  * See http://www.deneholme.net/tom/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 acked)
19 {
20 	struct tcp_sock *tp = tcp_sk(sk);
21 
22 	if (!tcp_is_cwnd_limited(sk))
23 		return;
24 
25 	if (tp->snd_cwnd <= tp->snd_ssthresh)
26 		tcp_slow_start(tp, acked);
27 	else
28 		tcp_cong_avoid_ai(tp, min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT));
29 }
30 
31 static u32 tcp_scalable_ssthresh(struct sock *sk)
32 {
33 	const struct tcp_sock *tp = tcp_sk(sk);
34 	return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);
35 }
36 
37 
38 static struct tcp_congestion_ops tcp_scalable __read_mostly = {
39 	.ssthresh	= tcp_scalable_ssthresh,
40 	.cong_avoid	= tcp_scalable_cong_avoid,
41 
42 	.owner		= THIS_MODULE,
43 	.name		= "scalable",
44 };
45 
46 static int __init tcp_scalable_register(void)
47 {
48 	return tcp_register_congestion_control(&tcp_scalable);
49 }
50 
51 static void __exit tcp_scalable_unregister(void)
52 {
53 	tcp_unregister_congestion_control(&tcp_scalable);
54 }
55 
56 module_init(tcp_scalable_register);
57 module_exit(tcp_scalable_unregister);
58 
59 MODULE_AUTHOR("John Heffner");
60 MODULE_LICENSE("GPL");
61 MODULE_DESCRIPTION("Scalable TCP");
62