1 /* 2 * Binary Increase Congestion control for TCP 3 * 4 * This is from the implementation of BICTCP in 5 * Lison-Xu, Kahaled Harfoush, and Injong Rhee. 6 * "Binary Increase Congestion Control for Fast, Long Distance 7 * Networks" in InfoComm 2004 8 * Available from: 9 * http://www.csc.ncsu.edu/faculty/rhee/export/bitcp.pdf 10 * 11 * Unless BIC is enabled and congestion window is large 12 * this behaves the same as the original Reno. 13 */ 14 15 #include <linux/config.h> 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 = 100; 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->loss_cwnd = 0; 67 ca->last_cwnd = 0; 68 ca->last_time = 0; 69 ca->epoch_start = 0; 70 ca->delayed_ack = 2 << ACK_RATIO_SHIFT; 71 } 72 73 static void bictcp_init(struct sock *sk) 74 { 75 bictcp_reset(inet_csk_ca(sk)); 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_time_stamp - ca->last_time) <= HZ / 32) 87 return; 88 89 ca->last_cwnd = cwnd; 90 ca->last_time = tcp_time_stamp; 91 92 if (ca->epoch_start == 0) /* record the beginning of an epoch */ 93 ca->epoch_start = tcp_time_stamp; 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->loss_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, 141 u32 seq_rtt, u32 in_flight, int data_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, in_flight)) 147 return; 148 149 if (tp->snd_cwnd <= tp->snd_ssthresh) 150 tcp_slow_start(tp); 151 else { 152 bictcp_update(ca, tp->snd_cwnd); 153 154 /* In dangerous area, increase slowly. 155 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd 156 */ 157 if (tp->snd_cwnd_cnt >= ca->cnt) { 158 if (tp->snd_cwnd < tp->snd_cwnd_clamp) 159 tp->snd_cwnd++; 160 tp->snd_cwnd_cnt = 0; 161 } else 162 tp->snd_cwnd_cnt++; 163 } 164 165 } 166 167 /* 168 * behave like Reno until low_window is reached, 169 * then increase congestion window slowly 170 */ 171 static u32 bictcp_recalc_ssthresh(struct sock *sk) 172 { 173 const struct tcp_sock *tp = tcp_sk(sk); 174 struct bictcp *ca = inet_csk_ca(sk); 175 176 ca->epoch_start = 0; /* end of epoch */ 177 178 /* Wmax and fast convergence */ 179 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) 180 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) 181 / (2 * BICTCP_BETA_SCALE); 182 else 183 ca->last_max_cwnd = tp->snd_cwnd; 184 185 ca->loss_cwnd = tp->snd_cwnd; 186 187 188 if (tp->snd_cwnd <= low_window) 189 return max(tp->snd_cwnd >> 1U, 2U); 190 else 191 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); 192 } 193 194 static u32 bictcp_undo_cwnd(struct sock *sk) 195 { 196 const struct tcp_sock *tp = tcp_sk(sk); 197 const struct bictcp *ca = inet_csk_ca(sk); 198 return max(tp->snd_cwnd, ca->last_max_cwnd); 199 } 200 201 static u32 bictcp_min_cwnd(struct sock *sk) 202 { 203 const struct tcp_sock *tp = tcp_sk(sk); 204 return tp->snd_ssthresh; 205 } 206 207 static void bictcp_state(struct sock *sk, u8 new_state) 208 { 209 if (new_state == TCP_CA_Loss) 210 bictcp_reset(inet_csk_ca(sk)); 211 } 212 213 /* Track delayed acknowledgment ratio using sliding window 214 * ratio = (15*ratio + sample) / 16 215 */ 216 static void bictcp_acked(struct sock *sk, u32 cnt) 217 { 218 const struct inet_connection_sock *icsk = inet_csk(sk); 219 220 if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) { 221 struct bictcp *ca = inet_csk_ca(sk); 222 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; 223 ca->delayed_ack += cnt; 224 } 225 } 226 227 228 static struct tcp_congestion_ops bictcp = { 229 .init = bictcp_init, 230 .ssthresh = bictcp_recalc_ssthresh, 231 .cong_avoid = bictcp_cong_avoid, 232 .set_state = bictcp_state, 233 .undo_cwnd = bictcp_undo_cwnd, 234 .min_cwnd = bictcp_min_cwnd, 235 .pkts_acked = bictcp_acked, 236 .owner = THIS_MODULE, 237 .name = "bic", 238 }; 239 240 static int __init bictcp_register(void) 241 { 242 BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); 243 return tcp_register_congestion_control(&bictcp); 244 } 245 246 static void __exit bictcp_unregister(void) 247 { 248 tcp_unregister_congestion_control(&bictcp); 249 } 250 251 module_init(bictcp_register); 252 module_exit(bictcp_unregister); 253 254 MODULE_AUTHOR("Stephen Hemminger"); 255 MODULE_LICENSE("GPL"); 256 MODULE_DESCRIPTION("BIC TCP"); 257