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 = 32; 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 tcp_sock *tp) 90 { 91 bictcp_reset(tcp_ca(tp)); 92 if (initial_ssthresh) 93 tp->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 tcp_sock *tp, int flag) 160 { 161 struct bictcp *ca = tcp_ca(tp); 162 u32 dist, delay; 163 164 /* No time stamp */ 165 if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) || 166 /* Discard delay samples right after fast recovery */ 167 tcp_time_stamp < ca->epoch_start + HZ || 168 /* this delay samples may not be accurate */ 169 flag == 0) { 170 ca->last_delay = 0; 171 goto notlow; 172 } 173 174 delay = ca->last_delay<<3; /* use the same scale as tp->srtt*/ 175 ca->last_delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr; 176 if (delay == 0) /* no previous delay sample */ 177 goto notlow; 178 179 /* first time call or link delay decreases */ 180 if (ca->delay_min == 0 || ca->delay_min > delay) { 181 ca->delay_min = ca->delay_max = delay; 182 goto notlow; 183 } 184 185 if (ca->delay_max < delay) 186 ca->delay_max = delay; 187 188 /* utilization is low, if avg delay < dist*threshold 189 for checking_period time */ 190 dist = ca->delay_max - ca->delay_min; 191 if (dist <= ca->delay_min>>6 || 192 tp->srtt - ca->delay_min >= (dist*low_utilization_threshold)>>10) 193 goto notlow; 194 195 if (ca->low_utilization_start == 0) { 196 ca->low_utilization = 0; 197 ca->low_utilization_start = tcp_time_stamp; 198 } else if ((s32)(tcp_time_stamp - ca->low_utilization_start) 199 > low_utilization_period*HZ) { 200 ca->low_utilization = 1; 201 } 202 203 return; 204 205 notlow: 206 ca->low_utilization = 0; 207 ca->low_utilization_start = 0; 208 209 } 210 211 static void bictcp_cong_avoid(struct tcp_sock *tp, u32 ack, 212 u32 seq_rtt, u32 in_flight, int data_acked) 213 { 214 struct bictcp *ca = tcp_ca(tp); 215 216 bictcp_low_utilization(tp, data_acked); 217 218 if (in_flight < tp->snd_cwnd) 219 return; 220 221 if (tp->snd_cwnd <= tp->snd_ssthresh) { 222 /* In "safe" area, increase. */ 223 if (tp->snd_cwnd < tp->snd_cwnd_clamp) 224 tp->snd_cwnd++; 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 tcp_sock *tp) 246 { 247 struct bictcp *ca = tcp_ca(tp); 248 249 ca->epoch_start = 0; /* end of epoch */ 250 251 /* in case of wrong delay_max*/ 252 if (ca->delay_min > 0 && ca->delay_max > ca->delay_min) 253 ca->delay_max = ca->delay_min 254 + ((ca->delay_max - ca->delay_min)* 90) / 100; 255 256 /* Wmax and fast convergence */ 257 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) 258 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) 259 / (2 * BICTCP_BETA_SCALE); 260 else 261 ca->last_max_cwnd = tp->snd_cwnd; 262 263 ca->loss_cwnd = tp->snd_cwnd; 264 265 266 if (tp->snd_cwnd <= low_window) 267 return max(tp->snd_cwnd >> 1U, 2U); 268 else 269 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); 270 } 271 272 static u32 bictcp_undo_cwnd(struct tcp_sock *tp) 273 { 274 struct bictcp *ca = tcp_ca(tp); 275 276 return max(tp->snd_cwnd, ca->last_max_cwnd); 277 } 278 279 static u32 bictcp_min_cwnd(struct tcp_sock *tp) 280 { 281 return tp->snd_ssthresh; 282 } 283 284 static void bictcp_state(struct tcp_sock *tp, u8 new_state) 285 { 286 if (new_state == TCP_CA_Loss) 287 bictcp_reset(tcp_ca(tp)); 288 } 289 290 /* Track delayed acknowledgement ratio using sliding window 291 * ratio = (15*ratio + sample) / 16 292 */ 293 static void bictcp_acked(struct tcp_sock *tp, u32 cnt) 294 { 295 if (cnt > 0 && tp->ca_state == TCP_CA_Open) { 296 struct bictcp *ca = tcp_ca(tp); 297 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; 298 ca->delayed_ack += cnt; 299 } 300 } 301 302 303 static struct tcp_congestion_ops bictcp = { 304 .init = bictcp_init, 305 .ssthresh = bictcp_recalc_ssthresh, 306 .cong_avoid = bictcp_cong_avoid, 307 .set_state = bictcp_state, 308 .undo_cwnd = bictcp_undo_cwnd, 309 .min_cwnd = bictcp_min_cwnd, 310 .pkts_acked = bictcp_acked, 311 .owner = THIS_MODULE, 312 .name = "bic", 313 }; 314 315 static int __init bictcp_register(void) 316 { 317 BUG_ON(sizeof(struct bictcp) > TCP_CA_PRIV_SIZE); 318 return tcp_register_congestion_control(&bictcp); 319 } 320 321 static void __exit bictcp_unregister(void) 322 { 323 tcp_unregister_congestion_control(&bictcp); 324 } 325 326 module_init(bictcp_register); 327 module_exit(bictcp_unregister); 328 329 MODULE_AUTHOR("Stephen Hemminger"); 330 MODULE_LICENSE("GPL"); 331 MODULE_DESCRIPTION("BIC TCP"); 332