1 /* 2 * Binary Increase Congestion control for TCP 3 * Home page: 4 * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC 5 * This is from the implementation of BICTCP in 6 * Lison-Xu, Kahaled Harfoush, and Injong Rhee. 7 * "Binary Increase Congestion Control for Fast, Long Distance 8 * Networks" in InfoComm 2004 9 * Available from: 10 * http://netsrv.csc.ncsu.edu/export/bitcp.pdf 11 * 12 * Unless BIC is enabled and congestion window is large 13 * this behaves the same as the original Reno. 14 */ 15 16 #include <linux/mm.h> 17 #include <linux/module.h> 18 #include <net/tcp.h> 19 20 #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation 21 * max_cwnd = snd_cwnd * beta 22 */ 23 #define BICTCP_B 4 /* 24 * In binary search, 25 * go to point (max+min)/N 26 */ 27 28 static int fast_convergence = 1; 29 static int max_increment = 16; 30 static int low_window = 14; 31 static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */ 32 static int initial_ssthresh; 33 static int smooth_part = 20; 34 35 module_param(fast_convergence, int, 0644); 36 MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence"); 37 module_param(max_increment, int, 0644); 38 MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search"); 39 module_param(low_window, int, 0644); 40 MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)"); 41 module_param(beta, int, 0644); 42 MODULE_PARM_DESC(beta, "beta for multiplicative increase"); 43 module_param(initial_ssthresh, int, 0644); 44 MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold"); 45 module_param(smooth_part, int, 0644); 46 MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax"); 47 48 /* BIC TCP Parameters */ 49 struct bictcp { 50 u32 cnt; /* increase cwnd by 1 after ACKs */ 51 u32 last_max_cwnd; /* last maximum snd_cwnd */ 52 u32 loss_cwnd; /* congestion window at last loss */ 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 ca->loss_cwnd = 0; 76 77 if (initial_ssthresh) 78 tcp_sk(sk)->snd_ssthresh = initial_ssthresh; 79 } 80 81 /* 82 * Compute congestion window to use. 83 */ 84 static inline void bictcp_update(struct bictcp *ca, u32 cwnd) 85 { 86 if (ca->last_cwnd == cwnd && 87 (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32) 88 return; 89 90 ca->last_cwnd = cwnd; 91 ca->last_time = tcp_time_stamp; 92 93 if (ca->epoch_start == 0) /* record the beginning of an epoch */ 94 ca->epoch_start = tcp_time_stamp; 95 96 /* start off normal */ 97 if (cwnd <= low_window) { 98 ca->cnt = cwnd; 99 return; 100 } 101 102 /* binary increase */ 103 if (cwnd < ca->last_max_cwnd) { 104 __u32 dist = (ca->last_max_cwnd - cwnd) 105 / BICTCP_B; 106 107 if (dist > max_increment) 108 /* linear increase */ 109 ca->cnt = cwnd / max_increment; 110 else if (dist <= 1U) 111 /* binary search increase */ 112 ca->cnt = (cwnd * smooth_part) / BICTCP_B; 113 else 114 /* binary search increase */ 115 ca->cnt = cwnd / dist; 116 } else { 117 /* slow start AMD linear increase */ 118 if (cwnd < ca->last_max_cwnd + BICTCP_B) 119 /* slow start */ 120 ca->cnt = (cwnd * smooth_part) / BICTCP_B; 121 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1)) 122 /* slow start */ 123 ca->cnt = (cwnd * (BICTCP_B-1)) 124 / (cwnd - ca->last_max_cwnd); 125 else 126 /* linear increase */ 127 ca->cnt = cwnd / max_increment; 128 } 129 130 /* if in slow start or link utilization is very low */ 131 if (ca->last_max_cwnd == 0) { 132 if (ca->cnt > 20) /* increase cwnd 5% per RTT */ 133 ca->cnt = 20; 134 } 135 136 ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; 137 if (ca->cnt == 0) /* cannot be zero */ 138 ca->cnt = 1; 139 } 140 141 static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked) 142 { 143 struct tcp_sock *tp = tcp_sk(sk); 144 struct bictcp *ca = inet_csk_ca(sk); 145 146 if (!tcp_is_cwnd_limited(sk)) 147 return; 148 149 if (tcp_in_slow_start(tp)) 150 tcp_slow_start(tp, acked); 151 else { 152 bictcp_update(ca, tp->snd_cwnd); 153 tcp_cong_avoid_ai(tp, ca->cnt, 1); 154 } 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 ca->loss_cwnd = tp->snd_cwnd; 176 177 if (tp->snd_cwnd <= low_window) 178 return max(tp->snd_cwnd >> 1U, 2U); 179 else 180 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); 181 } 182 183 static u32 bictcp_undo_cwnd(struct sock *sk) 184 { 185 const struct tcp_sock *tp = tcp_sk(sk); 186 const struct bictcp *ca = inet_csk_ca(sk); 187 188 return max(tp->snd_cwnd, ca->loss_cwnd); 189 } 190 191 static void bictcp_state(struct sock *sk, u8 new_state) 192 { 193 if (new_state == TCP_CA_Loss) 194 bictcp_reset(inet_csk_ca(sk)); 195 } 196 197 /* Track delayed acknowledgment ratio using sliding window 198 * ratio = (15*ratio + sample) / 16 199 */ 200 static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt) 201 { 202 const struct inet_connection_sock *icsk = inet_csk(sk); 203 204 if (icsk->icsk_ca_state == TCP_CA_Open) { 205 struct bictcp *ca = inet_csk_ca(sk); 206 207 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; 208 ca->delayed_ack += cnt; 209 } 210 } 211 212 static struct tcp_congestion_ops bictcp __read_mostly = { 213 .init = bictcp_init, 214 .ssthresh = bictcp_recalc_ssthresh, 215 .cong_avoid = bictcp_cong_avoid, 216 .set_state = bictcp_state, 217 .undo_cwnd = bictcp_undo_cwnd, 218 .pkts_acked = bictcp_acked, 219 .owner = THIS_MODULE, 220 .name = "bic", 221 }; 222 223 static int __init bictcp_register(void) 224 { 225 BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); 226 return tcp_register_congestion_control(&bictcp); 227 } 228 229 static void __exit bictcp_unregister(void) 230 { 231 tcp_unregister_congestion_control(&bictcp); 232 } 233 234 module_init(bictcp_register); 235 module_exit(bictcp_unregister); 236 237 MODULE_AUTHOR("Stephen Hemminger"); 238 MODULE_LICENSE("GPL"); 239 MODULE_DESCRIPTION("BIC TCP"); 240