1 /* 2 * TCP CUBIC: Binary Increase Congestion control for TCP v2.0 3 * 4 * This is from the implementation of CUBIC TCP in 5 * Injong Rhee, Lisong Xu. 6 * "CUBIC: A New TCP-Friendly High-Speed TCP Variant 7 * in PFLDnet 2005 8 * Available from: 9 * http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf 10 * 11 * Unless CUBIC 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 #include <asm/div64.h> 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 #define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */ 29 30 static int fast_convergence = 1; 31 static int max_increment = 16; 32 static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */ 33 static int initial_ssthresh = 100; 34 static int bic_scale = 41; 35 static int tcp_friendliness = 1; 36 37 static u32 cube_rtt_scale; 38 static u32 beta_scale; 39 static u64 cube_factor; 40 41 /* Note parameters that are used for precomputing scale factors are read-only */ 42 module_param(fast_convergence, int, 0644); 43 MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence"); 44 module_param(max_increment, int, 0644); 45 MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search"); 46 module_param(beta, int, 0444); 47 MODULE_PARM_DESC(beta, "beta for multiplicative increase"); 48 module_param(initial_ssthresh, int, 0644); 49 MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold"); 50 module_param(bic_scale, int, 0444); 51 MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)"); 52 module_param(tcp_friendliness, int, 0644); 53 MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness"); 54 55 #include <asm/div64.h> 56 57 /* BIC TCP Parameters */ 58 struct bictcp { 59 u32 cnt; /* increase cwnd by 1 after ACKs */ 60 u32 last_max_cwnd; /* last maximum snd_cwnd */ 61 u32 loss_cwnd; /* congestion window at last loss */ 62 u32 last_cwnd; /* the last snd_cwnd */ 63 u32 last_time; /* time when updated last_cwnd */ 64 u32 bic_origin_point;/* origin point of bic function */ 65 u32 bic_K; /* time to origin point from the beginning of the current epoch */ 66 u32 delay_min; /* min delay */ 67 u32 epoch_start; /* beginning of an epoch */ 68 u32 ack_cnt; /* number of acks */ 69 u32 tcp_cwnd; /* estimated tcp cwnd */ 70 #define ACK_RATIO_SHIFT 4 71 u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ 72 }; 73 74 static inline void bictcp_reset(struct bictcp *ca) 75 { 76 ca->cnt = 0; 77 ca->last_max_cwnd = 0; 78 ca->loss_cwnd = 0; 79 ca->last_cwnd = 0; 80 ca->last_time = 0; 81 ca->bic_origin_point = 0; 82 ca->bic_K = 0; 83 ca->delay_min = 0; 84 ca->epoch_start = 0; 85 ca->delayed_ack = 2 << ACK_RATIO_SHIFT; 86 ca->ack_cnt = 0; 87 ca->tcp_cwnd = 0; 88 } 89 90 static void bictcp_init(struct sock *sk) 91 { 92 bictcp_reset(inet_csk_ca(sk)); 93 if (initial_ssthresh) 94 tcp_sk(sk)->snd_ssthresh = initial_ssthresh; 95 } 96 97 /* 64bit divisor, dividend and result. dynamic precision */ 98 static inline u_int64_t div64_64(u_int64_t dividend, u_int64_t divisor) 99 { 100 u_int32_t d = divisor; 101 102 if (divisor > 0xffffffffULL) { 103 unsigned int shift = fls(divisor >> 32); 104 105 d = divisor >> shift; 106 dividend >>= shift; 107 } 108 109 /* avoid 64 bit division if possible */ 110 if (dividend >> 32) 111 do_div(dividend, d); 112 else 113 dividend = (uint32_t) dividend / d; 114 115 return dividend; 116 } 117 118 /* 119 * calculate the cubic root of x using Newton-Raphson 120 */ 121 static u32 cubic_root(u64 a) 122 { 123 u32 x, x1; 124 125 /* Initial estimate is based on: 126 * cbrt(x) = exp(log(x) / 3) 127 */ 128 x = 1u << (fls64(a)/3); 129 130 /* 131 * Iteration based on: 132 * 2 133 * x = ( 2 * x + a / x ) / 3 134 * k+1 k k 135 */ 136 do { 137 x1 = x; 138 x = (2 * x + (uint32_t) div64_64(a, x*x)) / 3; 139 } while (abs(x1 - x) > 1); 140 141 return x; 142 } 143 144 /* 145 * Compute congestion window to use. 146 */ 147 static inline void bictcp_update(struct bictcp *ca, u32 cwnd) 148 { 149 u64 offs; 150 u32 delta, t, bic_target, min_cnt, max_cnt; 151 152 ca->ack_cnt++; /* count the number of ACKs */ 153 154 if (ca->last_cwnd == cwnd && 155 (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32) 156 return; 157 158 ca->last_cwnd = cwnd; 159 ca->last_time = tcp_time_stamp; 160 161 if (ca->epoch_start == 0) { 162 ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */ 163 ca->ack_cnt = 1; /* start counting */ 164 ca->tcp_cwnd = cwnd; /* syn with cubic */ 165 166 if (ca->last_max_cwnd <= cwnd) { 167 ca->bic_K = 0; 168 ca->bic_origin_point = cwnd; 169 } else { 170 /* Compute new K based on 171 * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ) 172 */ 173 ca->bic_K = cubic_root(cube_factor 174 * (ca->last_max_cwnd - cwnd)); 175 ca->bic_origin_point = ca->last_max_cwnd; 176 } 177 } 178 179 /* cubic function - calc*/ 180 /* calculate c * time^3 / rtt, 181 * while considering overflow in calculation of time^3 182 * (so time^3 is done by using 64 bit) 183 * and without the support of division of 64bit numbers 184 * (so all divisions are done by using 32 bit) 185 * also NOTE the unit of those veriables 186 * time = (t - K) / 2^bictcp_HZ 187 * c = bic_scale >> 10 188 * rtt = (srtt >> 3) / HZ 189 * !!! The following code does not have overflow problems, 190 * if the cwnd < 1 million packets !!! 191 */ 192 193 /* change the unit from HZ to bictcp_HZ */ 194 t = ((tcp_time_stamp + ca->delay_min - ca->epoch_start) 195 << BICTCP_HZ) / HZ; 196 197 if (t < ca->bic_K) /* t - K */ 198 offs = ca->bic_K - t; 199 else 200 offs = t - ca->bic_K; 201 202 /* c/rtt * (t-K)^3 */ 203 delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ); 204 if (t < ca->bic_K) /* below origin*/ 205 bic_target = ca->bic_origin_point - delta; 206 else /* above origin*/ 207 bic_target = ca->bic_origin_point + delta; 208 209 /* cubic function - calc bictcp_cnt*/ 210 if (bic_target > cwnd) { 211 ca->cnt = cwnd / (bic_target - cwnd); 212 } else { 213 ca->cnt = 100 * cwnd; /* very small increment*/ 214 } 215 216 if (ca->delay_min > 0) { 217 /* max increment = Smax * rtt / 0.1 */ 218 min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min); 219 if (ca->cnt < min_cnt) 220 ca->cnt = min_cnt; 221 } 222 223 /* slow start and low utilization */ 224 if (ca->loss_cwnd == 0) /* could be aggressive in slow start */ 225 ca->cnt = 50; 226 227 /* TCP Friendly */ 228 if (tcp_friendliness) { 229 u32 scale = beta_scale; 230 delta = (cwnd * scale) >> 3; 231 while (ca->ack_cnt > delta) { /* update tcp cwnd */ 232 ca->ack_cnt -= delta; 233 ca->tcp_cwnd++; 234 } 235 236 if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */ 237 delta = ca->tcp_cwnd - cwnd; 238 max_cnt = cwnd / delta; 239 if (ca->cnt > max_cnt) 240 ca->cnt = max_cnt; 241 } 242 } 243 244 ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; 245 if (ca->cnt == 0) /* cannot be zero */ 246 ca->cnt = 1; 247 } 248 249 250 /* Keep track of minimum rtt */ 251 static inline void measure_delay(struct sock *sk) 252 { 253 const struct tcp_sock *tp = tcp_sk(sk); 254 struct bictcp *ca = inet_csk_ca(sk); 255 u32 delay; 256 257 /* No time stamp */ 258 if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) || 259 /* Discard delay samples right after fast recovery */ 260 (s32)(tcp_time_stamp - ca->epoch_start) < HZ) 261 return; 262 263 delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr; 264 if (delay == 0) 265 delay = 1; 266 267 /* first time call or link delay decreases */ 268 if (ca->delay_min == 0 || ca->delay_min > delay) 269 ca->delay_min = delay; 270 } 271 272 static void bictcp_cong_avoid(struct sock *sk, u32 ack, 273 u32 seq_rtt, u32 in_flight, int data_acked) 274 { 275 struct tcp_sock *tp = tcp_sk(sk); 276 struct bictcp *ca = inet_csk_ca(sk); 277 278 if (data_acked) 279 measure_delay(sk); 280 281 if (!tcp_is_cwnd_limited(sk, in_flight)) 282 return; 283 284 if (tp->snd_cwnd <= tp->snd_ssthresh) 285 tcp_slow_start(tp); 286 else { 287 bictcp_update(ca, tp->snd_cwnd); 288 289 /* In dangerous area, increase slowly. 290 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd 291 */ 292 if (tp->snd_cwnd_cnt >= ca->cnt) { 293 if (tp->snd_cwnd < tp->snd_cwnd_clamp) 294 tp->snd_cwnd++; 295 tp->snd_cwnd_cnt = 0; 296 } else 297 tp->snd_cwnd_cnt++; 298 } 299 300 } 301 302 static u32 bictcp_recalc_ssthresh(struct sock *sk) 303 { 304 const struct tcp_sock *tp = tcp_sk(sk); 305 struct bictcp *ca = inet_csk_ca(sk); 306 307 ca->epoch_start = 0; /* end of epoch */ 308 309 /* Wmax and fast convergence */ 310 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) 311 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) 312 / (2 * BICTCP_BETA_SCALE); 313 else 314 ca->last_max_cwnd = tp->snd_cwnd; 315 316 ca->loss_cwnd = tp->snd_cwnd; 317 318 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); 319 } 320 321 static u32 bictcp_undo_cwnd(struct sock *sk) 322 { 323 struct bictcp *ca = inet_csk_ca(sk); 324 325 return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd); 326 } 327 328 static u32 bictcp_min_cwnd(struct sock *sk) 329 { 330 return tcp_sk(sk)->snd_ssthresh; 331 } 332 333 static void bictcp_state(struct sock *sk, u8 new_state) 334 { 335 if (new_state == TCP_CA_Loss) 336 bictcp_reset(inet_csk_ca(sk)); 337 } 338 339 /* Track delayed acknowledgment ratio using sliding window 340 * ratio = (15*ratio + sample) / 16 341 */ 342 static void bictcp_acked(struct sock *sk, u32 cnt) 343 { 344 const struct inet_connection_sock *icsk = inet_csk(sk); 345 346 if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) { 347 struct bictcp *ca = inet_csk_ca(sk); 348 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; 349 ca->delayed_ack += cnt; 350 } 351 } 352 353 354 static struct tcp_congestion_ops cubictcp = { 355 .init = bictcp_init, 356 .ssthresh = bictcp_recalc_ssthresh, 357 .cong_avoid = bictcp_cong_avoid, 358 .set_state = bictcp_state, 359 .undo_cwnd = bictcp_undo_cwnd, 360 .min_cwnd = bictcp_min_cwnd, 361 .pkts_acked = bictcp_acked, 362 .owner = THIS_MODULE, 363 .name = "cubic", 364 }; 365 366 static int __init cubictcp_register(void) 367 { 368 BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); 369 370 /* Precompute a bunch of the scaling factors that are used per-packet 371 * based on SRTT of 100ms 372 */ 373 374 beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta); 375 376 cube_rtt_scale = (bic_scale << 3) / 10; /* 1024*c/rtt */ 377 378 /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3 379 * so K = cubic_root( (wmax-cwnd)*rtt/c ) 380 * the unit of K is bictcp_HZ=2^10, not HZ 381 * 382 * c = bic_scale >> 10 383 * rtt = 100ms 384 * 385 * the following code has been designed and tested for 386 * cwnd < 1 million packets 387 * RTT < 100 seconds 388 * HZ < 1,000,00 (corresponding to 10 nano-second) 389 */ 390 391 /* 1/c * 2^2*bictcp_HZ * srtt */ 392 cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */ 393 394 /* divide by bic_scale and by constant Srtt (100ms) */ 395 do_div(cube_factor, bic_scale * 10); 396 397 return tcp_register_congestion_control(&cubictcp); 398 } 399 400 static void __exit cubictcp_unregister(void) 401 { 402 tcp_unregister_congestion_control(&cubictcp); 403 } 404 405 module_init(cubictcp_register); 406 module_exit(cubictcp_unregister); 407 408 MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger"); 409 MODULE_LICENSE("GPL"); 410 MODULE_DESCRIPTION("CUBIC TCP"); 411 MODULE_VERSION("2.0"); 412