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/config.h> 10 #include <linux/module.h> 11 #include <net/tcp.h> 12 13 14 /* From AIMD tables from RFC 3649 appendix B, 15 * with fixed-point MD scaled <<8. 16 */ 17 static const struct hstcp_aimd_val { 18 unsigned int cwnd; 19 unsigned int md; 20 } hstcp_aimd_vals[] = { 21 { 38, 128, /* 0.50 */ }, 22 { 118, 112, /* 0.44 */ }, 23 { 221, 104, /* 0.41 */ }, 24 { 347, 98, /* 0.38 */ }, 25 { 495, 93, /* 0.37 */ }, 26 { 663, 89, /* 0.35 */ }, 27 { 851, 86, /* 0.34 */ }, 28 { 1058, 83, /* 0.33 */ }, 29 { 1284, 81, /* 0.32 */ }, 30 { 1529, 78, /* 0.31 */ }, 31 { 1793, 76, /* 0.30 */ }, 32 { 2076, 74, /* 0.29 */ }, 33 { 2378, 72, /* 0.28 */ }, 34 { 2699, 71, /* 0.28 */ }, 35 { 3039, 69, /* 0.27 */ }, 36 { 3399, 68, /* 0.27 */ }, 37 { 3778, 66, /* 0.26 */ }, 38 { 4177, 65, /* 0.26 */ }, 39 { 4596, 64, /* 0.25 */ }, 40 { 5036, 62, /* 0.25 */ }, 41 { 5497, 61, /* 0.24 */ }, 42 { 5979, 60, /* 0.24 */ }, 43 { 6483, 59, /* 0.23 */ }, 44 { 7009, 58, /* 0.23 */ }, 45 { 7558, 57, /* 0.22 */ }, 46 { 8130, 56, /* 0.22 */ }, 47 { 8726, 55, /* 0.22 */ }, 48 { 9346, 54, /* 0.21 */ }, 49 { 9991, 53, /* 0.21 */ }, 50 { 10661, 52, /* 0.21 */ }, 51 { 11358, 52, /* 0.20 */ }, 52 { 12082, 51, /* 0.20 */ }, 53 { 12834, 50, /* 0.20 */ }, 54 { 13614, 49, /* 0.19 */ }, 55 { 14424, 48, /* 0.19 */ }, 56 { 15265, 48, /* 0.19 */ }, 57 { 16137, 47, /* 0.19 */ }, 58 { 17042, 46, /* 0.18 */ }, 59 { 17981, 45, /* 0.18 */ }, 60 { 18955, 45, /* 0.18 */ }, 61 { 19965, 44, /* 0.17 */ }, 62 { 21013, 43, /* 0.17 */ }, 63 { 22101, 43, /* 0.17 */ }, 64 { 23230, 42, /* 0.17 */ }, 65 { 24402, 41, /* 0.16 */ }, 66 { 25618, 41, /* 0.16 */ }, 67 { 26881, 40, /* 0.16 */ }, 68 { 28193, 39, /* 0.16 */ }, 69 { 29557, 39, /* 0.15 */ }, 70 { 30975, 38, /* 0.15 */ }, 71 { 32450, 38, /* 0.15 */ }, 72 { 33986, 37, /* 0.15 */ }, 73 { 35586, 36, /* 0.14 */ }, 74 { 37253, 36, /* 0.14 */ }, 75 { 38992, 35, /* 0.14 */ }, 76 { 40808, 35, /* 0.14 */ }, 77 { 42707, 34, /* 0.13 */ }, 78 { 44694, 33, /* 0.13 */ }, 79 { 46776, 33, /* 0.13 */ }, 80 { 48961, 32, /* 0.13 */ }, 81 { 51258, 32, /* 0.13 */ }, 82 { 53677, 31, /* 0.12 */ }, 83 { 56230, 30, /* 0.12 */ }, 84 { 58932, 30, /* 0.12 */ }, 85 { 61799, 29, /* 0.12 */ }, 86 { 64851, 28, /* 0.11 */ }, 87 { 68113, 28, /* 0.11 */ }, 88 { 71617, 27, /* 0.11 */ }, 89 { 75401, 26, /* 0.10 */ }, 90 { 79517, 26, /* 0.10 */ }, 91 { 84035, 25, /* 0.10 */ }, 92 { 89053, 24, /* 0.10 */ }, 93 }; 94 95 #define HSTCP_AIMD_MAX ARRAY_SIZE(hstcp_aimd_vals) 96 97 struct hstcp { 98 u32 ai; 99 }; 100 101 static int max_ssthresh = 100; 102 module_param(max_ssthresh, int, 0644); 103 MODULE_PARM_DESC(max_ssthresh, "limited slow start threshold (RFC3742)"); 104 105 static void hstcp_init(struct sock *sk) 106 { 107 struct tcp_sock *tp = tcp_sk(sk); 108 struct hstcp *ca = inet_csk_ca(sk); 109 110 ca->ai = 0; 111 112 /* Ensure the MD arithmetic works. This is somewhat pedantic, 113 * since I don't think we will see a cwnd this large. :) */ 114 tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128); 115 } 116 117 static void hstcp_cong_avoid(struct sock *sk, u32 adk, u32 rtt, 118 u32 in_flight, int data_acked) 119 { 120 struct tcp_sock *tp = tcp_sk(sk); 121 struct hstcp *ca = inet_csk_ca(sk); 122 123 if (!tcp_is_cwnd_limited(sk, in_flight)) 124 return; 125 126 if (tp->snd_cwnd <= tp->snd_ssthresh) { 127 /* RFC3742: limited slow start 128 * the window is increased by 1/K MSS for each arriving ACK, 129 * for K = int(cwnd/(0.5 max_ssthresh)) 130 */ 131 if (max_ssthresh > 0 && tp->snd_cwnd > max_ssthresh) { 132 u32 k = max(tp->snd_cwnd / (max_ssthresh >> 1), 1U); 133 if (++tp->snd_cwnd_cnt >= k) { 134 if (tp->snd_cwnd < tp->snd_cwnd_clamp) 135 tp->snd_cwnd++; 136 tp->snd_cwnd_cnt = 0; 137 } 138 } else { 139 if (tp->snd_cwnd < tp->snd_cwnd_clamp) 140 tp->snd_cwnd++; 141 } 142 } else { 143 /* Update AIMD parameters */ 144 if (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd) { 145 while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd && 146 ca->ai < HSTCP_AIMD_MAX - 1) 147 ca->ai++; 148 } else if (tp->snd_cwnd < hstcp_aimd_vals[ca->ai].cwnd) { 149 while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd && 150 ca->ai > 0) 151 ca->ai--; 152 } 153 154 /* Do additive increase */ 155 if (tp->snd_cwnd < tp->snd_cwnd_clamp) { 156 /* cwnd = cwnd + a(w) / cwnd */ 157 tp->snd_cwnd_cnt += ca->ai + 1; 158 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) { 159 tp->snd_cwnd_cnt -= tp->snd_cwnd; 160 tp->snd_cwnd++; 161 } 162 } 163 } 164 } 165 166 static u32 hstcp_ssthresh(struct sock *sk) 167 { 168 const struct tcp_sock *tp = tcp_sk(sk); 169 const struct hstcp *ca = inet_csk_ca(sk); 170 171 /* Do multiplicative decrease */ 172 return max(tp->snd_cwnd - ((tp->snd_cwnd * hstcp_aimd_vals[ca->ai].md) >> 8), 2U); 173 } 174 175 176 static struct tcp_congestion_ops tcp_highspeed = { 177 .init = hstcp_init, 178 .ssthresh = hstcp_ssthresh, 179 .cong_avoid = hstcp_cong_avoid, 180 .min_cwnd = tcp_reno_min_cwnd, 181 182 .owner = THIS_MODULE, 183 .name = "highspeed" 184 }; 185 186 static int __init hstcp_register(void) 187 { 188 BUG_ON(sizeof(struct hstcp) > ICSK_CA_PRIV_SIZE); 189 return tcp_register_congestion_control(&tcp_highspeed); 190 } 191 192 static void __exit hstcp_unregister(void) 193 { 194 tcp_unregister_congestion_control(&tcp_highspeed); 195 } 196 197 module_init(hstcp_register); 198 module_exit(hstcp_unregister); 199 200 MODULE_AUTHOR("John Heffner"); 201 MODULE_LICENSE("GPL"); 202 MODULE_DESCRIPTION("High Speed TCP"); 203