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, val: 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(type: &tcp_highspeed); |
174 | } |
175 | |
176 | static void __exit hstcp_unregister(void) |
177 | { |
178 | tcp_unregister_congestion_control(type: &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 | |