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