1 // SPDX-License-Identifier: GPL-2.0-only
2 /* Tom Kelly's Scalable TCP
3 *
4 * See http://www.deneholme.net/tom/scalable/
5 *
6 * John Heffner <jheffner@sc.edu>
7 */
8
9 #include <linux/module.h>
10 #include <net/tcp.h>
11
12 /* These factors derived from the recommended values in the aer:
13 * .01 and and 7/8. We use 50 instead of 100 to account for
14 * delayed ack.
15 */
16 #define TCP_SCALABLE_AI_CNT 50U
17 #define TCP_SCALABLE_MD_SCALE 3
18
tcp_scalable_cong_avoid(struct sock * sk,u32 ack,u32 acked)19 static void tcp_scalable_cong_avoid(struct sock *sk, u32 ack, u32 acked)
20 {
21 struct tcp_sock *tp = tcp_sk(sk);
22
23 if (!tcp_is_cwnd_limited(sk))
24 return;
25
26 if (tcp_in_slow_start(tp))
27 tcp_slow_start(tp, acked);
28 else
29 tcp_cong_avoid_ai(tp, min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT),
30 1);
31 }
32
tcp_scalable_ssthresh(struct sock * sk)33 static u32 tcp_scalable_ssthresh(struct sock *sk)
34 {
35 const struct tcp_sock *tp = tcp_sk(sk);
36
37 return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);
38 }
39
40 static struct tcp_congestion_ops tcp_scalable __read_mostly = {
41 .ssthresh = tcp_scalable_ssthresh,
42 .undo_cwnd = tcp_reno_undo_cwnd,
43 .cong_avoid = tcp_scalable_cong_avoid,
44
45 .owner = THIS_MODULE,
46 .name = "scalable",
47 };
48
tcp_scalable_register(void)49 static int __init tcp_scalable_register(void)
50 {
51 return tcp_register_congestion_control(&tcp_scalable);
52 }
53
tcp_scalable_unregister(void)54 static void __exit tcp_scalable_unregister(void)
55 {
56 tcp_unregister_congestion_control(&tcp_scalable);
57 }
58
59 module_init(tcp_scalable_register);
60 module_exit(tcp_scalable_unregister);
61
62 MODULE_AUTHOR("John Heffner");
63 MODULE_LICENSE("GPL");
64 MODULE_DESCRIPTION("Scalable TCP");
65