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 7/8.
14  */
15 #define TCP_SCALABLE_AI_CNT	100U
16 #define TCP_SCALABLE_MD_SCALE	3
17 
tcp_scalable_cong_avoid(struct sock * sk,u32 ack,u32 acked)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 (tcp_in_slow_start(tp)) {
26 		acked = tcp_slow_start(tp, acked);
27 		if (!acked)
28 			return;
29 	}
30 	tcp_cong_avoid_ai(tp, min(tcp_snd_cwnd(tp), TCP_SCALABLE_AI_CNT),
31 			  acked);
32 }
33 
tcp_scalable_ssthresh(struct sock * sk)34 static u32 tcp_scalable_ssthresh(struct sock *sk)
35 {
36 	const struct tcp_sock *tp = tcp_sk(sk);
37 
38 	return max(tcp_snd_cwnd(tp) - (tcp_snd_cwnd(tp)>>TCP_SCALABLE_MD_SCALE), 2U);
39 }
40 
41 static struct tcp_congestion_ops tcp_scalable __read_mostly = {
42 	.ssthresh	= tcp_scalable_ssthresh,
43 	.undo_cwnd	= tcp_reno_undo_cwnd,
44 	.cong_avoid	= tcp_scalable_cong_avoid,
45 
46 	.owner		= THIS_MODULE,
47 	.name		= "scalable",
48 };
49 
tcp_scalable_register(void)50 static int __init tcp_scalable_register(void)
51 {
52 	return tcp_register_congestion_control(&tcp_scalable);
53 }
54 
tcp_scalable_unregister(void)55 static void __exit tcp_scalable_unregister(void)
56 {
57 	tcp_unregister_congestion_control(&tcp_scalable);
58 }
59 
60 module_init(tcp_scalable_register);
61 module_exit(tcp_scalable_unregister);
62 
63 MODULE_AUTHOR("John Heffner");
64 MODULE_LICENSE("GPL");
65 MODULE_DESCRIPTION("Scalable TCP");
66