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 low_utilization_threshold = 153; 34 static int low_utilization_period = 2; 35 static int initial_ssthresh = 100; 36 static int smooth_part = 20; 37 38 module_param(fast_convergence, int, 0644); 39 MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence"); 40 module_param(max_increment, int, 0644); 41 MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search"); 42 module_param(low_window, int, 0644); 43 MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)"); 44 module_param(beta, int, 0644); 45 MODULE_PARM_DESC(beta, "beta for multiplicative increase"); 46 module_param(low_utilization_threshold, int, 0644); 47 MODULE_PARM_DESC(low_utilization_threshold, "percent (scaled by 1024) for low utilization mode"); 48 module_param(low_utilization_period, int, 0644); 49 MODULE_PARM_DESC(low_utilization_period, "if average delay exceeds then goto to low utilization mode (seconds)"); 50 module_param(initial_ssthresh, int, 0644); 51 MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold"); 52 module_param(smooth_part, int, 0644); 53 MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax"); 54 55 56 /* BIC TCP Parameters */ 57 struct bictcp { 58 u32 cnt; /* increase cwnd by 1 after ACKs */ 59 u32 last_max_cwnd; /* last maximum snd_cwnd */ 60 u32 loss_cwnd; /* congestion window at last loss */ 61 u32 last_cwnd; /* the last snd_cwnd */ 62 u32 last_time; /* time when updated last_cwnd */ 63 u32 delay_min; /* min delay */ 64 u32 delay_max; /* max delay */ 65 u32 last_delay; 66 u8 low_utilization;/* 0: high; 1: low */ 67 u32 low_utilization_start; /* starting time of low utilization detection*/ 68 u32 epoch_start; /* beginning of an epoch */ 69 #define ACK_RATIO_SHIFT 4 70 u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ 71 }; 72 73 static inline void bictcp_reset(struct bictcp *ca) 74 { 75 ca->cnt = 0; 76 ca->last_max_cwnd = 0; 77 ca->loss_cwnd = 0; 78 ca->last_cwnd = 0; 79 ca->last_time = 0; 80 ca->delay_min = 0; 81 ca->delay_max = 0; 82 ca->last_delay = 0; 83 ca->low_utilization = 0; 84 ca->low_utilization_start = 0; 85 ca->epoch_start = 0; 86 ca->delayed_ack = 2 << ACK_RATIO_SHIFT; 87 } 88 89 static void bictcp_init(struct sock *sk) 90 { 91 bictcp_reset(inet_csk_ca(sk)); 92 if (initial_ssthresh) 93 tcp_sk(sk)->snd_ssthresh = initial_ssthresh; 94 } 95 96 /* 97 * Compute congestion window to use. 98 */ 99 static inline void bictcp_update(struct bictcp *ca, u32 cwnd) 100 { 101 if (ca->last_cwnd == cwnd && 102 (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32) 103 return; 104 105 ca->last_cwnd = cwnd; 106 ca->last_time = tcp_time_stamp; 107 108 if (ca->epoch_start == 0) /* record the beginning of an epoch */ 109 ca->epoch_start = tcp_time_stamp; 110 111 /* start off normal */ 112 if (cwnd <= low_window) { 113 ca->cnt = cwnd; 114 return; 115 } 116 117 /* binary increase */ 118 if (cwnd < ca->last_max_cwnd) { 119 __u32 dist = (ca->last_max_cwnd - cwnd) 120 / BICTCP_B; 121 122 if (dist > max_increment) 123 /* linear increase */ 124 ca->cnt = cwnd / max_increment; 125 else if (dist <= 1U) 126 /* binary search increase */ 127 ca->cnt = (cwnd * smooth_part) / BICTCP_B; 128 else 129 /* binary search increase */ 130 ca->cnt = cwnd / dist; 131 } else { 132 /* slow start AMD linear increase */ 133 if (cwnd < ca->last_max_cwnd + BICTCP_B) 134 /* slow start */ 135 ca->cnt = (cwnd * smooth_part) / BICTCP_B; 136 else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1)) 137 /* slow start */ 138 ca->cnt = (cwnd * (BICTCP_B-1)) 139 / (cwnd - ca->last_max_cwnd); 140 else 141 /* linear increase */ 142 ca->cnt = cwnd / max_increment; 143 } 144 145 /* if in slow start or link utilization is very low */ 146 if ( ca->loss_cwnd == 0 || 147 (cwnd > ca->loss_cwnd && ca->low_utilization)) { 148 if (ca->cnt > 20) /* increase cwnd 5% per RTT */ 149 ca->cnt = 20; 150 } 151 152 ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; 153 if (ca->cnt == 0) /* cannot be zero */ 154 ca->cnt = 1; 155 } 156 157 158 /* Detect low utilization in congestion avoidance */ 159 static inline void bictcp_low_utilization(struct sock *sk, int flag) 160 { 161 const struct tcp_sock *tp = tcp_sk(sk); 162 struct bictcp *ca = inet_csk_ca(sk); 163 u32 dist, delay; 164 165 /* No time stamp */ 166 if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) || 167 /* Discard delay samples right after fast recovery */ 168 tcp_time_stamp < ca->epoch_start + HZ || 169 /* this delay samples may not be accurate */ 170 flag == 0) { 171 ca->last_delay = 0; 172 goto notlow; 173 } 174 175 delay = ca->last_delay<<3; /* use the same scale as tp->srtt*/ 176 ca->last_delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr; 177 if (delay == 0) /* no previous delay sample */ 178 goto notlow; 179 180 /* first time call or link delay decreases */ 181 if (ca->delay_min == 0 || ca->delay_min > delay) { 182 ca->delay_min = ca->delay_max = delay; 183 goto notlow; 184 } 185 186 if (ca->delay_max < delay) 187 ca->delay_max = delay; 188 189 /* utilization is low, if avg delay < dist*threshold 190 for checking_period time */ 191 dist = ca->delay_max - ca->delay_min; 192 if (dist <= ca->delay_min>>6 || 193 tp->srtt - ca->delay_min >= (dist*low_utilization_threshold)>>10) 194 goto notlow; 195 196 if (ca->low_utilization_start == 0) { 197 ca->low_utilization = 0; 198 ca->low_utilization_start = tcp_time_stamp; 199 } else if ((s32)(tcp_time_stamp - ca->low_utilization_start) 200 > low_utilization_period*HZ) { 201 ca->low_utilization = 1; 202 } 203 204 return; 205 206 notlow: 207 ca->low_utilization = 0; 208 ca->low_utilization_start = 0; 209 210 } 211 212 static void bictcp_cong_avoid(struct sock *sk, u32 ack, 213 u32 seq_rtt, u32 in_flight, int data_acked) 214 { 215 struct tcp_sock *tp = tcp_sk(sk); 216 struct bictcp *ca = inet_csk_ca(sk); 217 218 bictcp_low_utilization(sk, data_acked); 219 220 if (!tcp_is_cwnd_limited(sk, in_flight)) 221 return; 222 223 if (tp->snd_cwnd <= tp->snd_ssthresh) 224 tcp_slow_start(tp); 225 else { 226 bictcp_update(ca, tp->snd_cwnd); 227 228 /* In dangerous area, increase slowly. 229 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd 230 */ 231 if (tp->snd_cwnd_cnt >= ca->cnt) { 232 if (tp->snd_cwnd < tp->snd_cwnd_clamp) 233 tp->snd_cwnd++; 234 tp->snd_cwnd_cnt = 0; 235 } else 236 tp->snd_cwnd_cnt++; 237 } 238 239 } 240 241 /* 242 * behave like Reno until low_window is reached, 243 * then increase congestion window slowly 244 */ 245 static u32 bictcp_recalc_ssthresh(struct sock *sk) 246 { 247 const struct tcp_sock *tp = tcp_sk(sk); 248 struct bictcp *ca = inet_csk_ca(sk); 249 250 ca->epoch_start = 0; /* end of epoch */ 251 252 /* in case of wrong delay_max*/ 253 if (ca->delay_min > 0 && ca->delay_max > ca->delay_min) 254 ca->delay_max = ca->delay_min 255 + ((ca->delay_max - ca->delay_min)* 90) / 100; 256 257 /* Wmax and fast convergence */ 258 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) 259 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) 260 / (2 * BICTCP_BETA_SCALE); 261 else 262 ca->last_max_cwnd = tp->snd_cwnd; 263 264 ca->loss_cwnd = tp->snd_cwnd; 265 266 267 if (tp->snd_cwnd <= low_window) 268 return max(tp->snd_cwnd >> 1U, 2U); 269 else 270 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); 271 } 272 273 static u32 bictcp_undo_cwnd(struct sock *sk) 274 { 275 const struct tcp_sock *tp = tcp_sk(sk); 276 const struct bictcp *ca = inet_csk_ca(sk); 277 return max(tp->snd_cwnd, ca->last_max_cwnd); 278 } 279 280 static u32 bictcp_min_cwnd(struct sock *sk) 281 { 282 const struct tcp_sock *tp = tcp_sk(sk); 283 return tp->snd_ssthresh; 284 } 285 286 static void bictcp_state(struct sock *sk, u8 new_state) 287 { 288 if (new_state == TCP_CA_Loss) 289 bictcp_reset(inet_csk_ca(sk)); 290 } 291 292 /* Track delayed acknowledgement ratio using sliding window 293 * ratio = (15*ratio + sample) / 16 294 */ 295 static void bictcp_acked(struct sock *sk, u32 cnt) 296 { 297 const struct inet_connection_sock *icsk = inet_csk(sk); 298 299 if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) { 300 struct bictcp *ca = inet_csk_ca(sk); 301 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; 302 ca->delayed_ack += cnt; 303 } 304 } 305 306 307 static struct tcp_congestion_ops bictcp = { 308 .init = bictcp_init, 309 .ssthresh = bictcp_recalc_ssthresh, 310 .cong_avoid = bictcp_cong_avoid, 311 .set_state = bictcp_state, 312 .undo_cwnd = bictcp_undo_cwnd, 313 .min_cwnd = bictcp_min_cwnd, 314 .pkts_acked = bictcp_acked, 315 .owner = THIS_MODULE, 316 .name = "bic", 317 }; 318 319 static int __init bictcp_register(void) 320 { 321 BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); 322 return tcp_register_congestion_control(&bictcp); 323 } 324 325 static void __exit bictcp_unregister(void) 326 { 327 tcp_unregister_congestion_control(&bictcp); 328 } 329 330 module_init(bictcp_register); 331 module_exit(bictcp_unregister); 332 333 MODULE_AUTHOR("Stephen Hemminger"); 334 MODULE_LICENSE("GPL"); 335 MODULE_DESCRIPTION("BIC TCP"); 336