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 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 50 /* BIC TCP Parameters */ 51 struct bictcp { 52 u32 cnt; /* increase cwnd by 1 after ACKs */ 53 u32 last_max_cwnd; /* last maximum snd_cwnd */ 54 u32 loss_cwnd; /* congestion window at last loss */ 55 u32 last_cwnd; /* the last snd_cwnd */ 56 u32 last_time; /* time when updated last_cwnd */ 57 u32 epoch_start; /* beginning of an epoch */ 58 #define ACK_RATIO_SHIFT 4 59 u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ 60 }; 61 62 static inline void bictcp_reset(struct bictcp *ca) 63 { 64 ca->cnt = 0; 65 ca->last_max_cwnd = 0; 66 ca->last_cwnd = 0; 67 ca->last_time = 0; 68 ca->epoch_start = 0; 69 ca->delayed_ack = 2 << ACK_RATIO_SHIFT; 70 } 71 72 static void bictcp_init(struct sock *sk) 73 { 74 struct bictcp *ca = inet_csk_ca(sk); 75 76 bictcp_reset(ca); 77 ca->loss_cwnd = 0; 78 79 if (initial_ssthresh) 80 tcp_sk(sk)->snd_ssthresh = initial_ssthresh; 81 } 82 83 /* 84 * Compute congestion window to use. 85 */ 86 static inline void bictcp_update(struct bictcp *ca, u32 cwnd) 87 { 88 if (ca->last_cwnd == cwnd && 89 (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32) 90 return; 91 92 ca->last_cwnd = cwnd; 93 ca->last_time = tcp_time_stamp; 94 95 if (ca->epoch_start == 0) /* record the beginning of an epoch */ 96 ca->epoch_start = tcp_time_stamp; 97 98 /* start off normal */ 99 if (cwnd <= low_window) { 100 ca->cnt = cwnd; 101 return; 102 } 103 104 /* binary increase */ 105 if (cwnd < ca->last_max_cwnd) { 106 __u32 dist = (ca->last_max_cwnd - cwnd) 107 / BICTCP_B; 108 109 if (dist > max_increment) 110 /* linear increase */ 111 ca->cnt = cwnd / max_increment; 112 else if (dist <= 1U) 113 /* binary search increase */ 114 ca->cnt = (cwnd * smooth_part) / BICTCP_B; 115 else 116 /* binary search increase */ 117 ca->cnt = cwnd / dist; 118 } else { 119 /* slow start AMD linear increase */ 120 if (cwnd < ca->last_max_cwnd + BICTCP_B) 121 /* slow start */ 122 ca->cnt = (cwnd * smooth_part) / BICTCP_B; 123 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1)) 124 /* slow start */ 125 ca->cnt = (cwnd * (BICTCP_B-1)) 126 / (cwnd - ca->last_max_cwnd); 127 else 128 /* linear increase */ 129 ca->cnt = cwnd / max_increment; 130 } 131 132 /* if in slow start or link utilization is very low */ 133 if (ca->last_max_cwnd == 0) { 134 if (ca->cnt > 20) /* increase cwnd 5% per RTT */ 135 ca->cnt = 20; 136 } 137 138 ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; 139 if (ca->cnt == 0) /* cannot be zero */ 140 ca->cnt = 1; 141 } 142 143 static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) 144 { 145 struct tcp_sock *tp = tcp_sk(sk); 146 struct bictcp *ca = inet_csk_ca(sk); 147 148 if (!tcp_is_cwnd_limited(sk, in_flight)) 149 return; 150 151 if (tp->snd_cwnd <= tp->snd_ssthresh) 152 tcp_slow_start(tp); 153 else { 154 bictcp_update(ca, tp->snd_cwnd); 155 tcp_cong_avoid_ai(tp, ca->cnt); 156 } 157 158 } 159 160 /* 161 * behave like Reno until low_window is reached, 162 * then increase congestion window slowly 163 */ 164 static u32 bictcp_recalc_ssthresh(struct sock *sk) 165 { 166 const struct tcp_sock *tp = tcp_sk(sk); 167 struct bictcp *ca = inet_csk_ca(sk); 168 169 ca->epoch_start = 0; /* end of epoch */ 170 171 /* Wmax and fast convergence */ 172 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) 173 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) 174 / (2 * BICTCP_BETA_SCALE); 175 else 176 ca->last_max_cwnd = tp->snd_cwnd; 177 178 ca->loss_cwnd = tp->snd_cwnd; 179 180 181 if (tp->snd_cwnd <= low_window) 182 return max(tp->snd_cwnd >> 1U, 2U); 183 else 184 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); 185 } 186 187 static u32 bictcp_undo_cwnd(struct sock *sk) 188 { 189 const struct tcp_sock *tp = tcp_sk(sk); 190 const struct bictcp *ca = inet_csk_ca(sk); 191 return max(tp->snd_cwnd, ca->loss_cwnd); 192 } 193 194 static void bictcp_state(struct sock *sk, u8 new_state) 195 { 196 if (new_state == TCP_CA_Loss) 197 bictcp_reset(inet_csk_ca(sk)); 198 } 199 200 /* Track delayed acknowledgment ratio using sliding window 201 * ratio = (15*ratio + sample) / 16 202 */ 203 static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt) 204 { 205 const struct inet_connection_sock *icsk = inet_csk(sk); 206 207 if (icsk->icsk_ca_state == TCP_CA_Open) { 208 struct bictcp *ca = inet_csk_ca(sk); 209 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; 210 ca->delayed_ack += cnt; 211 } 212 } 213 214 215 static struct tcp_congestion_ops bictcp __read_mostly = { 216 .init = bictcp_init, 217 .ssthresh = bictcp_recalc_ssthresh, 218 .cong_avoid = bictcp_cong_avoid, 219 .set_state = bictcp_state, 220 .undo_cwnd = bictcp_undo_cwnd, 221 .pkts_acked = bictcp_acked, 222 .owner = THIS_MODULE, 223 .name = "bic", 224 }; 225 226 static int __init bictcp_register(void) 227 { 228 BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); 229 return tcp_register_congestion_control(&bictcp); 230 } 231 232 static void __exit bictcp_unregister(void) 233 { 234 tcp_unregister_congestion_control(&bictcp); 235 } 236 237 module_init(bictcp_register); 238 module_exit(bictcp_unregister); 239 240 MODULE_AUTHOR("Stephen Hemminger"); 241 MODULE_LICENSE("GPL"); 242 MODULE_DESCRIPTION("BIC TCP"); 243