1/*
2 * Sally Floyd's High Speed TCP (RFC 3649) congestion control
3 *
4 * See http://www.icir.org/floyd/hstcp.html
5 *
6 * John Heffner <jheffner@psc.edu>
7 */
8
9#include <linux/module.h>
10#include <net/tcp.h>
11
12
13/* From AIMD tables from RFC 3649 appendix B,
14 * with fixed-point MD scaled <<8.
15 */
16static const struct hstcp_aimd_val {
17	unsigned int cwnd;
18	unsigned int md;
19} hstcp_aimd_vals[] = {
20 {     38,  128, /*  0.50 */ },
21 {    118,  112, /*  0.44 */ },
22 {    221,  104, /*  0.41 */ },
23 {    347,   98, /*  0.38 */ },
24 {    495,   93, /*  0.37 */ },
25 {    663,   89, /*  0.35 */ },
26 {    851,   86, /*  0.34 */ },
27 {   1058,   83, /*  0.33 */ },
28 {   1284,   81, /*  0.32 */ },
29 {   1529,   78, /*  0.31 */ },
30 {   1793,   76, /*  0.30 */ },
31 {   2076,   74, /*  0.29 */ },
32 {   2378,   72, /*  0.28 */ },
33 {   2699,   71, /*  0.28 */ },
34 {   3039,   69, /*  0.27 */ },
35 {   3399,   68, /*  0.27 */ },
36 {   3778,   66, /*  0.26 */ },
37 {   4177,   65, /*  0.26 */ },
38 {   4596,   64, /*  0.25 */ },
39 {   5036,   62, /*  0.25 */ },
40 {   5497,   61, /*  0.24 */ },
41 {   5979,   60, /*  0.24 */ },
42 {   6483,   59, /*  0.23 */ },
43 {   7009,   58, /*  0.23 */ },
44 {   7558,   57, /*  0.22 */ },
45 {   8130,   56, /*  0.22 */ },
46 {   8726,   55, /*  0.22 */ },
47 {   9346,   54, /*  0.21 */ },
48 {   9991,   53, /*  0.21 */ },
49 {  10661,   52, /*  0.21 */ },
50 {  11358,   52, /*  0.20 */ },
51 {  12082,   51, /*  0.20 */ },
52 {  12834,   50, /*  0.20 */ },
53 {  13614,   49, /*  0.19 */ },
54 {  14424,   48, /*  0.19 */ },
55 {  15265,   48, /*  0.19 */ },
56 {  16137,   47, /*  0.19 */ },
57 {  17042,   46, /*  0.18 */ },
58 {  17981,   45, /*  0.18 */ },
59 {  18955,   45, /*  0.18 */ },
60 {  19965,   44, /*  0.17 */ },
61 {  21013,   43, /*  0.17 */ },
62 {  22101,   43, /*  0.17 */ },
63 {  23230,   42, /*  0.17 */ },
64 {  24402,   41, /*  0.16 */ },
65 {  25618,   41, /*  0.16 */ },
66 {  26881,   40, /*  0.16 */ },
67 {  28193,   39, /*  0.16 */ },
68 {  29557,   39, /*  0.15 */ },
69 {  30975,   38, /*  0.15 */ },
70 {  32450,   38, /*  0.15 */ },
71 {  33986,   37, /*  0.15 */ },
72 {  35586,   36, /*  0.14 */ },
73 {  37253,   36, /*  0.14 */ },
74 {  38992,   35, /*  0.14 */ },
75 {  40808,   35, /*  0.14 */ },
76 {  42707,   34, /*  0.13 */ },
77 {  44694,   33, /*  0.13 */ },
78 {  46776,   33, /*  0.13 */ },
79 {  48961,   32, /*  0.13 */ },
80 {  51258,   32, /*  0.13 */ },
81 {  53677,   31, /*  0.12 */ },
82 {  56230,   30, /*  0.12 */ },
83 {  58932,   30, /*  0.12 */ },
84 {  61799,   29, /*  0.12 */ },
85 {  64851,   28, /*  0.11 */ },
86 {  68113,   28, /*  0.11 */ },
87 {  71617,   27, /*  0.11 */ },
88 {  75401,   26, /*  0.10 */ },
89 {  79517,   26, /*  0.10 */ },
90 {  84035,   25, /*  0.10 */ },
91 {  89053,   24, /*  0.10 */ },
92};
93
94#define HSTCP_AIMD_MAX	ARRAY_SIZE(hstcp_aimd_vals)
95
96struct hstcp {
97	u32	ai;
98};
99
100static void hstcp_init(struct sock *sk)
101{
102	struct tcp_sock *tp = tcp_sk(sk);
103	struct hstcp *ca = inet_csk_ca(sk);
104
105	ca->ai = 0;
106
107	/* Ensure the MD arithmetic works.  This is somewhat pedantic,
108	 * since I don't think we will see a cwnd this large. :) */
109	tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128);
110}
111
112static void hstcp_cong_avoid(struct sock *sk, u32 adk, u32 in_flight)
113{
114	struct tcp_sock *tp = tcp_sk(sk);
115	struct hstcp *ca = inet_csk_ca(sk);
116
117	if (!tcp_is_cwnd_limited(sk, in_flight))
118		return;
119
120	if (tp->snd_cwnd <= tp->snd_ssthresh)
121		tcp_slow_start(tp);
122	else {
123		/* Update AIMD parameters.
124		 *
125		 * We want to guarantee that:
126		 *     hstcp_aimd_vals[ca->ai-1].cwnd <
127		 *     snd_cwnd <=
128		 *     hstcp_aimd_vals[ca->ai].cwnd
129		 */
130		if (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd) {
131			while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd &&
132			       ca->ai < HSTCP_AIMD_MAX - 1)
133				ca->ai++;
134		} else if (ca->ai && tp->snd_cwnd <= hstcp_aimd_vals[ca->ai-1].cwnd) {
135			while (ca->ai && tp->snd_cwnd <= hstcp_aimd_vals[ca->ai-1].cwnd)
136				ca->ai--;
137		}
138
139		/* Do additive increase */
140		if (tp->snd_cwnd < tp->snd_cwnd_clamp) {
141			/* cwnd = cwnd + a(w) / cwnd */
142			tp->snd_cwnd_cnt += ca->ai + 1;
143			if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
144				tp->snd_cwnd_cnt -= tp->snd_cwnd;
145				tp->snd_cwnd++;
146			}
147		}
148	}
149}
150
151static u32 hstcp_ssthresh(struct sock *sk)
152{
153	const struct tcp_sock *tp = tcp_sk(sk);
154	const struct hstcp *ca = inet_csk_ca(sk);
155
156	/* Do multiplicative decrease */
157	return max(tp->snd_cwnd - ((tp->snd_cwnd * hstcp_aimd_vals[ca->ai].md) >> 8), 2U);
158}
159
160
161static struct tcp_congestion_ops tcp_highspeed = {
162	.init		= hstcp_init,
163	.ssthresh	= hstcp_ssthresh,
164	.cong_avoid	= hstcp_cong_avoid,
165	.min_cwnd	= tcp_reno_min_cwnd,
166
167	.owner		= THIS_MODULE,
168	.name		= "highspeed"
169};
170
171static int __init hstcp_register(void)
172{
173	BUILD_BUG_ON(sizeof(struct hstcp) > ICSK_CA_PRIV_SIZE);
174	return tcp_register_congestion_control(&tcp_highspeed);
175}
176
177static void __exit hstcp_unregister(void)
178{
179	tcp_unregister_congestion_control(&tcp_highspeed);
180}
181
182module_init(hstcp_register);
183module_exit(hstcp_unregister);
184
185MODULE_AUTHOR("John Heffner");
186MODULE_LICENSE("GPL");
187MODULE_DESCRIPTION("High Speed TCP");
188