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