1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Sally Floyd's High Speed TCP (RFC 3649) congestion control
4 *
5 * See https://www.icir.org/floyd/hstcp.html
6 *
7 * John Heffner <jheffner@psc.edu>
8 */
9
10 #include <linux/module.h>
11 #include <net/tcp.h>
12
13 /* From AIMD tables from RFC 3649 appendix B,
14 * with fixed-point MD scaled <<8.
15 */
16 static 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
96 struct hstcp {
97 u32 ai;
98 };
99
100 static 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
112 static void hstcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
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))
118 return;
119
120 if (tcp_in_slow_start(tp))
121 tcp_slow_start(tp, acked);
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 (tcp_snd_cwnd(tp) > hstcp_aimd_vals[ca->ai].cwnd) {
131 while (tcp_snd_cwnd(tp) > hstcp_aimd_vals[ca->ai].cwnd &&
132 ca->ai < HSTCP_AIMD_MAX - 1)
133 ca->ai++;
134 } else if (ca->ai && tcp_snd_cwnd(tp) <= hstcp_aimd_vals[ca->ai-1].cwnd) {
135 while (ca->ai && tcp_snd_cwnd(tp) <= hstcp_aimd_vals[ca->ai-1].cwnd)
136 ca->ai--;
137 }
138
139 /* Do additive increase */
140 if (tcp_snd_cwnd(tp) < tp->snd_cwnd_clamp) {
141 /* cwnd = cwnd + a(w) / cwnd */
142 tp->snd_cwnd_cnt += ca->ai + 1;
143 if (tp->snd_cwnd_cnt >= tcp_snd_cwnd(tp)) {
144 tp->snd_cwnd_cnt -= tcp_snd_cwnd(tp);
145 tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
146 }
147 }
148 }
149 }
150
151 static u32 hstcp_ssthresh(struct sock *sk)
152 {
153 const struct tcp_sock *tp = tcp_sk(sk);
154 struct hstcp *ca = inet_csk_ca(sk);
155
156 /* Do multiplicative decrease */
157 return max(tcp_snd_cwnd(tp) - ((tcp_snd_cwnd(tp) * hstcp_aimd_vals[ca->ai].md) >> 8), 2U);
158 }
159
160 static struct tcp_congestion_ops tcp_highspeed __read_mostly = {
161 .init = hstcp_init,
162 .ssthresh = hstcp_ssthresh,
163 .undo_cwnd = tcp_reno_undo_cwnd,
164 .cong_avoid = hstcp_cong_avoid,
165
166 .owner = THIS_MODULE,
167 .name = "highspeed"
168 };
169
170 static int __init hstcp_register(void)
171 {
172 BUILD_BUG_ON(sizeof(struct hstcp) > ICSK_CA_PRIV_SIZE);
173 return tcp_register_congestion_control(&tcp_highspeed);
174 }
175
176 static void __exit hstcp_unregister(void)
177 {
178 tcp_unregister_congestion_control(&tcp_highspeed);
179 }
180
181 module_init(hstcp_register);
182 module_exit(hstcp_unregister);
183
184 MODULE_AUTHOR("John Heffner");
185 MODULE_LICENSE("GPL");
186 MODULE_DESCRIPTION("High Speed TCP");
187
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