1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Binary Increase Congestion control for TCP 4 * Home page: 5 * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC 6 * This is from the implementation of BICTCP in 7 * Lison-Xu, Kahaled Harfoush, and Injong Rhee. 8 * "Binary Increase Congestion Control for Fast, Long Distance 9 * Networks" in InfoComm 2004 10 * Available from: 11 * http://netsrv.csc.ncsu.edu/export/bitcp.pdf 12 * 13 * Unless BIC is enabled and congestion window is large 14 * this behaves the same as the original Reno. 15 */ 16 17 #include <linux/mm.h> 18 #include <linux/module.h> 19 #include <net/tcp.h> 20 21 #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation 22 * max_cwnd = snd_cwnd * beta 23 */ 24 #define BICTCP_B 4 /* 25 * In binary search, 26 * go to point (max+min)/N 27 */ 28 29 static int fast_convergence = 1; 30 static int max_increment = 16; 31 static int low_window = 14; 32 static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */ 33 static int initial_ssthresh; 34 static int smooth_part = 20; 35 36 module_param(fast_convergence, int, 0644); 37 MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence"); 38 module_param(max_increment, int, 0644); 39 MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search"); 40 module_param(low_window, int, 0644); 41 MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)"); 42 module_param(beta, int, 0644); 43 MODULE_PARM_DESC(beta, "beta for multiplicative increase"); 44 module_param(initial_ssthresh, int, 0644); 45 MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold"); 46 module_param(smooth_part, int, 0644); 47 MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax"); 48 49 /* BIC TCP Parameters */ 50 struct bictcp { 51 u32 cnt; /* increase cwnd by 1 after ACKs */ 52 u32 last_max_cwnd; /* last maximum snd_cwnd */ 53 u32 last_cwnd; /* the last snd_cwnd */ 54 u32 last_time; /* time when updated last_cwnd */ 55 u32 epoch_start; /* beginning of an epoch */ 56 #define ACK_RATIO_SHIFT 4 57 u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ 58 }; 59 60 static inline void bictcp_reset(struct bictcp *ca) 61 { 62 ca->cnt = 0; 63 ca->last_max_cwnd = 0; 64 ca->last_cwnd = 0; 65 ca->last_time = 0; 66 ca->epoch_start = 0; 67 ca->delayed_ack = 2 << ACK_RATIO_SHIFT; 68 } 69 70 static void bictcp_init(struct sock *sk) 71 { 72 struct bictcp *ca = inet_csk_ca(sk); 73 74 bictcp_reset(ca); 75 76 if (initial_ssthresh) 77 tcp_sk(sk)->snd_ssthresh = initial_ssthresh; 78 } 79 80 /* 81 * Compute congestion window to use. 82 */ 83 static inline void bictcp_update(struct bictcp *ca, u32 cwnd) 84 { 85 if (ca->last_cwnd == cwnd && 86 (s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32) 87 return; 88 89 ca->last_cwnd = cwnd; 90 ca->last_time = tcp_jiffies32; 91 92 if (ca->epoch_start == 0) /* record the beginning of an epoch */ 93 ca->epoch_start = tcp_jiffies32; 94 95 /* start off normal */ 96 if (cwnd <= low_window) { 97 ca->cnt = cwnd; 98 return; 99 } 100 101 /* binary increase */ 102 if (cwnd < ca->last_max_cwnd) { 103 __u32 dist = (ca->last_max_cwnd - cwnd) 104 / BICTCP_B; 105 106 if (dist > max_increment) 107 /* linear increase */ 108 ca->cnt = cwnd / max_increment; 109 else if (dist <= 1U) 110 /* binary search increase */ 111 ca->cnt = (cwnd * smooth_part) / BICTCP_B; 112 else 113 /* binary search increase */ 114 ca->cnt = cwnd / dist; 115 } else { 116 /* slow start AMD linear increase */ 117 if (cwnd < ca->last_max_cwnd + BICTCP_B) 118 /* slow start */ 119 ca->cnt = (cwnd * smooth_part) / BICTCP_B; 120 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1)) 121 /* slow start */ 122 ca->cnt = (cwnd * (BICTCP_B-1)) 123 / (cwnd - ca->last_max_cwnd); 124 else 125 /* linear increase */ 126 ca->cnt = cwnd / max_increment; 127 } 128 129 /* if in slow start or link utilization is very low */ 130 if (ca->last_max_cwnd == 0) { 131 if (ca->cnt > 20) /* increase cwnd 5% per RTT */ 132 ca->cnt = 20; 133 } 134 135 ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; 136 if (ca->cnt == 0) /* cannot be zero */ 137 ca->cnt = 1; 138 } 139 140 static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked) 141 { 142 struct tcp_sock *tp = tcp_sk(sk); 143 struct bictcp *ca = inet_csk_ca(sk); 144 145 if (!tcp_is_cwnd_limited(sk)) 146 return; 147 148 if (tcp_in_slow_start(tp)) { 149 acked = tcp_slow_start(tp, acked); 150 if (!acked) 151 return; 152 } 153 bictcp_update(ca, tp->snd_cwnd); 154 tcp_cong_avoid_ai(tp, ca->cnt, acked); 155 } 156 157 /* 158 * behave like Reno until low_window is reached, 159 * then increase congestion window slowly 160 */ 161 static u32 bictcp_recalc_ssthresh(struct sock *sk) 162 { 163 const struct tcp_sock *tp = tcp_sk(sk); 164 struct bictcp *ca = inet_csk_ca(sk); 165 166 ca->epoch_start = 0; /* end of epoch */ 167 168 /* Wmax and fast convergence */ 169 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) 170 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) 171 / (2 * BICTCP_BETA_SCALE); 172 else 173 ca->last_max_cwnd = tp->snd_cwnd; 174 175 if (tp->snd_cwnd <= low_window) 176 return max(tp->snd_cwnd >> 1U, 2U); 177 else 178 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); 179 } 180 181 static void bictcp_state(struct sock *sk, u8 new_state) 182 { 183 if (new_state == TCP_CA_Loss) 184 bictcp_reset(inet_csk_ca(sk)); 185 } 186 187 /* Track delayed acknowledgment ratio using sliding window 188 * ratio = (15*ratio + sample) / 16 189 */ 190 static void bictcp_acked(struct sock *sk, const struct ack_sample *sample) 191 { 192 const struct inet_connection_sock *icsk = inet_csk(sk); 193 194 if (icsk->icsk_ca_state == TCP_CA_Open) { 195 struct bictcp *ca = inet_csk_ca(sk); 196 197 ca->delayed_ack += sample->pkts_acked - 198 (ca->delayed_ack >> ACK_RATIO_SHIFT); 199 } 200 } 201 202 static struct tcp_congestion_ops bictcp __read_mostly = { 203 .init = bictcp_init, 204 .ssthresh = bictcp_recalc_ssthresh, 205 .cong_avoid = bictcp_cong_avoid, 206 .set_state = bictcp_state, 207 .undo_cwnd = tcp_reno_undo_cwnd, 208 .pkts_acked = bictcp_acked, 209 .owner = THIS_MODULE, 210 .name = "bic", 211 }; 212 213 static int __init bictcp_register(void) 214 { 215 BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); 216 return tcp_register_congestion_control(&bictcp); 217 } 218 219 static void __exit bictcp_unregister(void) 220 { 221 tcp_unregister_congestion_control(&bictcp); 222 } 223 224 module_init(bictcp_register); 225 module_exit(bictcp_unregister); 226 227 MODULE_AUTHOR("Stephen Hemminger"); 228 MODULE_LICENSE("GPL"); 229 MODULE_DESCRIPTION("BIC TCP"); 230