1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2008-2010 Lawrence Stewart <lstewart@freebsd.org> 5 * Copyright (c) 2010 The FreeBSD Foundation 6 * All rights reserved. 7 * 8 * This software was developed by Lawrence Stewart while studying at the Centre 9 * for Advanced Internet Architectures, Swinburne University of Technology, made 10 * possible in part by a grant from the Cisco University Research Program Fund 11 * at Community Foundation Silicon Valley. 12 * 13 * Portions of this software were developed at the Centre for Advanced 14 * Internet Architectures, Swinburne University of Technology, Melbourne, 15 * Australia by David Hayes under sponsorship from the FreeBSD Foundation. 16 * 17 * Redistribution and use in source and binary forms, with or without 18 * modification, are permitted provided that the following conditions 19 * are met: 20 * 1. Redistributions of source code must retain the above copyright 21 * notice, this list of conditions and the following disclaimer. 22 * 2. Redistributions in binary form must reproduce the above copyright 23 * notice, this list of conditions and the following disclaimer in the 24 * documentation and/or other materials provided with the distribution. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 */ 38 39 /* 40 * An implementation of the CUBIC congestion control algorithm for FreeBSD, 41 * based on the Internet Draft "draft-rhee-tcpm-cubic-02" by Rhee, Xu and Ha. 42 * Originally released as part of the NewTCP research project at Swinburne 43 * University of Technology's Centre for Advanced Internet Architectures, 44 * Melbourne, Australia, which was made possible in part by a grant from the 45 * Cisco University Research Program Fund at Community Foundation Silicon 46 * Valley. More details are available at: 47 * http://caia.swin.edu.au/urp/newtcp/ 48 */ 49 50 #include <sys/cdefs.h> 51 __FBSDID("$FreeBSD$"); 52 53 #include <sys/param.h> 54 #include <sys/kernel.h> 55 #include <sys/limits.h> 56 #include <sys/malloc.h> 57 #include <sys/module.h> 58 #include <sys/socket.h> 59 #include <sys/socketvar.h> 60 #include <sys/sysctl.h> 61 #include <sys/systm.h> 62 63 #include <net/vnet.h> 64 65 #include <net/route.h> 66 #include <net/route/nhop.h> 67 68 #include <netinet/in_pcb.h> 69 #include <netinet/tcp.h> 70 #include <netinet/tcp_seq.h> 71 #include <netinet/tcp_timer.h> 72 #include <netinet/tcp_var.h> 73 #include <netinet/tcp_log_buf.h> 74 #include <netinet/tcp_hpts.h> 75 #include <netinet/cc/cc.h> 76 #include <netinet/cc/cc_cubic.h> 77 #include <netinet/cc/cc_module.h> 78 79 static void cubic_ack_received(struct cc_var *ccv, uint16_t type); 80 static void cubic_cb_destroy(struct cc_var *ccv); 81 static int cubic_cb_init(struct cc_var *ccv, void *ptr); 82 static void cubic_cong_signal(struct cc_var *ccv, uint32_t type); 83 static void cubic_conn_init(struct cc_var *ccv); 84 static int cubic_mod_init(void); 85 static void cubic_post_recovery(struct cc_var *ccv); 86 static void cubic_record_rtt(struct cc_var *ccv); 87 static void cubic_ssthresh_update(struct cc_var *ccv, uint32_t maxseg); 88 static void cubic_after_idle(struct cc_var *ccv); 89 static size_t cubic_data_sz(void); 90 static void cubic_newround(struct cc_var *ccv, uint32_t round_cnt); 91 static void cubic_rttsample(struct cc_var *ccv, uint32_t usec_rtt, 92 uint32_t rxtcnt, uint32_t fas); 93 94 struct cc_algo cubic_cc_algo = { 95 .name = "cubic", 96 .ack_received = cubic_ack_received, 97 .cb_destroy = cubic_cb_destroy, 98 .cb_init = cubic_cb_init, 99 .cong_signal = cubic_cong_signal, 100 .conn_init = cubic_conn_init, 101 .mod_init = cubic_mod_init, 102 .post_recovery = cubic_post_recovery, 103 .after_idle = cubic_after_idle, 104 .cc_data_sz = cubic_data_sz, 105 .rttsample = cubic_rttsample, 106 .newround = cubic_newround 107 }; 108 109 static void 110 cubic_log_hystart_event(struct cc_var *ccv, struct cubic *cubicd, uint8_t mod, uint32_t flex1) 111 { 112 /* 113 * Types of logs (mod value) 114 * 1 - rtt_thresh in flex1, checking to see if RTT is to great. 115 * 2 - rtt is too great, rtt_thresh in flex1. 116 * 3 - CSS is active incr in flex1 117 * 4 - A new round is beginning flex1 is round count 118 * 5 - A new RTT measurement flex1 is the new measurement. 119 * 6 - We enter CA ssthresh is also in flex1. 120 * 7 - Socket option to change hystart executed opt.val in flex1. 121 * 8 - Back out of CSS into SS, flex1 is the css_baseline_minrtt 122 * 9 - We enter CA, via an ECN mark. 123 * 10 - We enter CA, via a loss. 124 * 11 - We have slipped out of SS into CA via cwnd growth. 125 * 12 - After idle has re-enabled hystart++ 126 */ 127 struct tcpcb *tp; 128 129 if (hystart_bblogs == 0) 130 return; 131 tp = ccv->ccvc.tcp; 132 if (tcp_bblogging_on(tp)) { 133 union tcp_log_stackspecific log; 134 struct timeval tv; 135 136 memset(&log, 0, sizeof(log)); 137 log.u_bbr.flex1 = flex1; 138 log.u_bbr.flex2 = cubicd->css_current_round_minrtt; 139 log.u_bbr.flex3 = cubicd->css_lastround_minrtt; 140 log.u_bbr.flex4 = cubicd->css_rttsample_count; 141 log.u_bbr.flex5 = cubicd->css_entered_at_round; 142 log.u_bbr.flex6 = cubicd->css_baseline_minrtt; 143 /* We only need bottom 16 bits of flags */ 144 log.u_bbr.flex7 = cubicd->flags & 0x0000ffff; 145 log.u_bbr.flex8 = mod; 146 log.u_bbr.epoch = cubicd->css_current_round; 147 log.u_bbr.timeStamp = tcp_get_usecs(&tv); 148 log.u_bbr.lt_epoch = cubicd->css_fas_at_css_entry; 149 log.u_bbr.pkts_out = cubicd->css_last_fas; 150 log.u_bbr.delivered = cubicd->css_lowrtt_fas; 151 log.u_bbr.pkt_epoch = ccv->flags; 152 TCP_LOG_EVENTP(tp, NULL, 153 &tptosocket(tp)->so_rcv, 154 &tptosocket(tp)->so_snd, 155 TCP_HYSTART, 0, 156 0, &log, false, &tv); 157 } 158 } 159 160 static void 161 cubic_does_slow_start(struct cc_var *ccv, struct cubic *cubicd) 162 { 163 /* 164 * In slow-start with ABC enabled and no RTO in sight? 165 * (Must not use abc_l_var > 1 if slow starting after 166 * an RTO. On RTO, snd_nxt = snd_una, so the 167 * snd_nxt == snd_max check is sufficient to 168 * handle this). 169 * 170 * XXXLAS: Find a way to signal SS after RTO that 171 * doesn't rely on tcpcb vars. 172 */ 173 u_int cw = CCV(ccv, snd_cwnd); 174 u_int incr = CCV(ccv, t_maxseg); 175 uint16_t abc_val; 176 177 cubicd->flags |= CUBICFLAG_IN_SLOWSTART; 178 if (ccv->flags & CCF_USE_LOCAL_ABC) 179 abc_val = ccv->labc; 180 else 181 abc_val = V_tcp_abc_l_var; 182 if ((ccv->flags & CCF_HYSTART_ALLOWED) && 183 (cubicd->flags & CUBICFLAG_HYSTART_ENABLED) && 184 ((cubicd->flags & CUBICFLAG_HYSTART_IN_CSS) == 0)) { 185 /* 186 * Hystart is allowed and still enabled and we are not yet 187 * in CSS. Lets check to see if we can make a decision on 188 * if we need to go into CSS. 189 */ 190 if ((cubicd->css_rttsample_count >= hystart_n_rttsamples) && 191 (cubicd->css_current_round_minrtt != 0xffffffff) && 192 (cubicd->css_lastround_minrtt != 0xffffffff)) { 193 uint32_t rtt_thresh; 194 195 /* Clamp (minrtt_thresh, lastround/8, maxrtt_thresh) */ 196 rtt_thresh = (cubicd->css_lastround_minrtt >> 3); 197 if (rtt_thresh < hystart_minrtt_thresh) 198 rtt_thresh = hystart_minrtt_thresh; 199 if (rtt_thresh > hystart_maxrtt_thresh) 200 rtt_thresh = hystart_maxrtt_thresh; 201 cubic_log_hystart_event(ccv, cubicd, 1, rtt_thresh); 202 203 if (cubicd->css_current_round_minrtt >= (cubicd->css_lastround_minrtt + rtt_thresh)) { 204 /* Enter CSS */ 205 cubicd->flags |= CUBICFLAG_HYSTART_IN_CSS; 206 cubicd->css_fas_at_css_entry = cubicd->css_lowrtt_fas; 207 /* 208 * The draft (v4) calls for us to set baseline to css_current_round_min 209 * but that can cause an oscillation. We probably shoudl be using 210 * css_lastround_minrtt, but the authors insist that will cause 211 * issues on exiting early. We will leave the draft version for now 212 * but I suspect this is incorrect. 213 */ 214 cubicd->css_baseline_minrtt = cubicd->css_current_round_minrtt; 215 cubicd->css_entered_at_round = cubicd->css_current_round; 216 cubic_log_hystart_event(ccv, cubicd, 2, rtt_thresh); 217 } 218 } 219 } 220 if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max)) 221 incr = min(ccv->bytes_this_ack, 222 ccv->nsegs * abc_val * 223 CCV(ccv, t_maxseg)); 224 else 225 incr = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg)); 226 227 /* Only if Hystart is enabled will the flag get set */ 228 if (cubicd->flags & CUBICFLAG_HYSTART_IN_CSS) { 229 incr /= hystart_css_growth_div; 230 cubic_log_hystart_event(ccv, cubicd, 3, incr); 231 } 232 /* ABC is on by default, so incr equals 0 frequently. */ 233 if (incr > 0) 234 CCV(ccv, snd_cwnd) = min((cw + incr), 235 TCP_MAXWIN << CCV(ccv, snd_scale)); 236 } 237 238 static void 239 cubic_ack_received(struct cc_var *ccv, uint16_t type) 240 { 241 struct cubic *cubic_data; 242 unsigned long w_tf, w_cubic_next; 243 int usecs_since_cong; 244 245 cubic_data = ccv->cc_data; 246 cubic_record_rtt(ccv); 247 248 /* 249 * For a regular ACK and we're not in cong/fast recovery and 250 * we're cwnd limited, always recalculate cwnd. 251 */ 252 if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) && 253 (ccv->flags & CCF_CWND_LIMITED)) { 254 /* Use the logic in NewReno ack_received() for slow start. */ 255 if (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) || 256 cubic_data->min_rtt_usecs == TCPTV_SRTTBASE) { 257 cubic_does_slow_start(ccv, cubic_data); 258 } else { 259 if (cubic_data->flags & CUBICFLAG_HYSTART_IN_CSS) { 260 /* 261 * We have slipped into CA with 262 * CSS active. Deactivate all. 263 */ 264 /* Turn off the CSS flag */ 265 cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 266 /* Disable use of CSS in the future except long idle */ 267 cubic_data->flags &= ~CUBICFLAG_HYSTART_ENABLED; 268 cubic_log_hystart_event(ccv, cubic_data, 11, CCV(ccv, snd_ssthresh)); 269 } 270 if ((cubic_data->flags & CUBICFLAG_RTO_EVENT) && 271 (cubic_data->flags & CUBICFLAG_IN_SLOWSTART)) { 272 /* RFC8312 Section 4.7 */ 273 cubic_data->flags &= ~(CUBICFLAG_RTO_EVENT | 274 CUBICFLAG_IN_SLOWSTART); 275 cubic_data->max_cwnd = CCV(ccv, snd_cwnd); 276 cubic_data->K = 0; 277 } else if (cubic_data->flags & (CUBICFLAG_IN_SLOWSTART | 278 CUBICFLAG_IN_APPLIMIT)) { 279 cubic_data->flags &= ~(CUBICFLAG_IN_SLOWSTART | 280 CUBICFLAG_IN_APPLIMIT); 281 cubic_data->t_last_cong = ticks; 282 cubic_data->K = cubic_k(cubic_data->max_cwnd / 283 CCV(ccv, t_maxseg)); 284 } 285 usecs_since_cong = (ticks - cubic_data->t_last_cong) * tick; 286 if (usecs_since_cong < 0) { 287 /* 288 * dragging t_last_cong along 289 */ 290 usecs_since_cong = INT_MAX; 291 cubic_data->t_last_cong = ticks - INT_MAX; 292 } 293 /* 294 * The mean RTT is used to best reflect the equations in 295 * the I-D. Using min_rtt in the tf_cwnd calculation 296 * causes w_tf to grow much faster than it should if the 297 * RTT is dominated by network buffering rather than 298 * propagation delay. 299 */ 300 w_tf = tf_cwnd(usecs_since_cong, cubic_data->mean_rtt_usecs, 301 cubic_data->max_cwnd, CCV(ccv, t_maxseg)); 302 303 w_cubic_next = cubic_cwnd(usecs_since_cong + 304 cubic_data->mean_rtt_usecs, 305 cubic_data->max_cwnd, 306 CCV(ccv, t_maxseg), 307 cubic_data->K); 308 309 ccv->flags &= ~CCF_ABC_SENTAWND; 310 311 if (w_cubic_next < w_tf) { 312 /* 313 * TCP-friendly region, follow tf 314 * cwnd growth. 315 */ 316 if (CCV(ccv, snd_cwnd) < w_tf) 317 CCV(ccv, snd_cwnd) = ulmin(w_tf, INT_MAX); 318 } else if (CCV(ccv, snd_cwnd) < w_cubic_next) { 319 /* 320 * Concave or convex region, follow CUBIC 321 * cwnd growth. 322 * Only update snd_cwnd, if it doesn't shrink. 323 */ 324 CCV(ccv, snd_cwnd) = ulmin(w_cubic_next, 325 INT_MAX); 326 } 327 328 /* 329 * If we're not in slow start and we're probing for a 330 * new cwnd limit at the start of a connection 331 * (happens when hostcache has a relevant entry), 332 * keep updating our current estimate of the 333 * max_cwnd. 334 */ 335 if (((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) && 336 cubic_data->max_cwnd < CCV(ccv, snd_cwnd)) { 337 cubic_data->max_cwnd = CCV(ccv, snd_cwnd); 338 cubic_data->K = cubic_k(cubic_data->max_cwnd / 339 CCV(ccv, t_maxseg)); 340 } 341 } 342 } else if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) && 343 !(ccv->flags & CCF_CWND_LIMITED)) { 344 cubic_data->flags |= CUBICFLAG_IN_APPLIMIT; 345 } 346 } 347 348 /* 349 * This is a CUBIC specific implementation of after_idle. 350 * - Reset cwnd by calling New Reno implementation of after_idle. 351 * - Reset t_last_cong. 352 */ 353 static void 354 cubic_after_idle(struct cc_var *ccv) 355 { 356 struct cubic *cubic_data; 357 358 cubic_data = ccv->cc_data; 359 360 cubic_data->max_cwnd = ulmax(cubic_data->max_cwnd, CCV(ccv, snd_cwnd)); 361 cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg)); 362 if ((cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) == 0) { 363 /* 364 * Re-enable hystart if we have been idle. 365 */ 366 cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 367 cubic_data->flags |= CUBICFLAG_HYSTART_ENABLED; 368 cubic_log_hystart_event(ccv, cubic_data, 12, CCV(ccv, snd_ssthresh)); 369 } 370 newreno_cc_after_idle(ccv); 371 cubic_data->t_last_cong = ticks; 372 } 373 374 static void 375 cubic_cb_destroy(struct cc_var *ccv) 376 { 377 free(ccv->cc_data, M_CC_MEM); 378 } 379 380 static size_t 381 cubic_data_sz(void) 382 { 383 return (sizeof(struct cubic)); 384 } 385 386 static int 387 cubic_cb_init(struct cc_var *ccv, void *ptr) 388 { 389 struct cubic *cubic_data; 390 391 INP_WLOCK_ASSERT(tptoinpcb(ccv->ccvc.tcp)); 392 if (ptr == NULL) { 393 cubic_data = malloc(sizeof(struct cubic), M_CC_MEM, M_NOWAIT|M_ZERO); 394 if (cubic_data == NULL) 395 return (ENOMEM); 396 } else 397 cubic_data = ptr; 398 399 /* Init some key variables with sensible defaults. */ 400 cubic_data->t_last_cong = ticks; 401 cubic_data->min_rtt_usecs = TCPTV_SRTTBASE; 402 cubic_data->mean_rtt_usecs = 1; 403 404 ccv->cc_data = cubic_data; 405 cubic_data->flags = CUBICFLAG_HYSTART_ENABLED; 406 /* At init set both to infinity */ 407 cubic_data->css_lastround_minrtt = 0xffffffff; 408 cubic_data->css_current_round_minrtt = 0xffffffff; 409 cubic_data->css_current_round = 0; 410 cubic_data->css_baseline_minrtt = 0xffffffff; 411 cubic_data->css_rttsample_count = 0; 412 cubic_data->css_entered_at_round = 0; 413 cubic_data->css_fas_at_css_entry = 0; 414 cubic_data->css_lowrtt_fas = 0; 415 cubic_data->css_last_fas = 0; 416 417 return (0); 418 } 419 420 /* 421 * Perform any necessary tasks before we enter congestion recovery. 422 */ 423 static void 424 cubic_cong_signal(struct cc_var *ccv, uint32_t type) 425 { 426 struct cubic *cubic_data; 427 u_int mss; 428 429 cubic_data = ccv->cc_data; 430 mss = tcp_maxseg(ccv->ccvc.tcp); 431 432 switch (type) { 433 case CC_NDUPACK: 434 if (cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) { 435 /* Make sure the flags are all off we had a loss */ 436 cubic_data->flags &= ~CUBICFLAG_HYSTART_ENABLED; 437 cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 438 cubic_log_hystart_event(ccv, cubic_data, 10, CCV(ccv, snd_ssthresh)); 439 } 440 if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) { 441 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { 442 cubic_ssthresh_update(ccv, mss); 443 cubic_data->flags |= CUBICFLAG_CONG_EVENT; 444 cubic_data->t_last_cong = ticks; 445 cubic_data->K = cubic_k(cubic_data->max_cwnd / mss); 446 } 447 ENTER_RECOVERY(CCV(ccv, t_flags)); 448 } 449 break; 450 451 case CC_ECN: 452 if (cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) { 453 /* Make sure the flags are all off we had a loss */ 454 cubic_data->flags &= ~CUBICFLAG_HYSTART_ENABLED; 455 cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 456 cubic_log_hystart_event(ccv, cubic_data, 9, CCV(ccv, snd_ssthresh)); 457 } 458 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { 459 cubic_ssthresh_update(ccv, mss); 460 cubic_data->flags |= CUBICFLAG_CONG_EVENT; 461 cubic_data->t_last_cong = ticks; 462 cubic_data->K = cubic_k(cubic_data->max_cwnd / mss); 463 CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh); 464 ENTER_CONGRECOVERY(CCV(ccv, t_flags)); 465 } 466 break; 467 468 case CC_RTO: 469 /* RFC8312 Section 4.7 */ 470 if (CCV(ccv, t_rxtshift) == 1) { 471 cubic_data->t_last_cong_prev = cubic_data->t_last_cong; 472 cubic_data->prev_max_cwnd_cp = cubic_data->prev_max_cwnd; 473 } 474 cubic_data->flags |= CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT; 475 cubic_data->prev_max_cwnd = cubic_data->max_cwnd; 476 CCV(ccv, snd_ssthresh) = ((uint64_t)CCV(ccv, snd_cwnd) * 477 CUBIC_BETA) >> CUBIC_SHIFT; 478 CCV(ccv, snd_cwnd) = mss; 479 break; 480 481 case CC_RTO_ERR: 482 cubic_data->flags &= ~(CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT); 483 cubic_data->max_cwnd = cubic_data->prev_max_cwnd; 484 cubic_data->prev_max_cwnd = cubic_data->prev_max_cwnd_cp; 485 cubic_data->t_last_cong = cubic_data->t_last_cong_prev; 486 cubic_data->K = cubic_k(cubic_data->max_cwnd / mss); 487 break; 488 } 489 } 490 491 static void 492 cubic_conn_init(struct cc_var *ccv) 493 { 494 struct cubic *cubic_data; 495 496 cubic_data = ccv->cc_data; 497 498 /* 499 * Ensure we have a sane initial value for max_cwnd recorded. Without 500 * this here bad things happen when entries from the TCP hostcache 501 * get used. 502 */ 503 cubic_data->max_cwnd = CCV(ccv, snd_cwnd); 504 } 505 506 static int 507 cubic_mod_init(void) 508 { 509 return (0); 510 } 511 512 /* 513 * Perform any necessary tasks before we exit congestion recovery. 514 */ 515 static void 516 cubic_post_recovery(struct cc_var *ccv) 517 { 518 struct cubic *cubic_data; 519 int pipe; 520 521 cubic_data = ccv->cc_data; 522 pipe = 0; 523 524 if (IN_FASTRECOVERY(CCV(ccv, t_flags))) { 525 /* 526 * If inflight data is less than ssthresh, set cwnd 527 * conservatively to avoid a burst of data, as suggested in 528 * the NewReno RFC. Otherwise, use the CUBIC method. 529 * 530 * XXXLAS: Find a way to do this without needing curack 531 */ 532 if (V_tcp_do_newsack) 533 pipe = tcp_compute_pipe(ccv->ccvc.tcp); 534 else 535 pipe = CCV(ccv, snd_max) - ccv->curack; 536 537 if (pipe < CCV(ccv, snd_ssthresh)) 538 /* 539 * Ensure that cwnd does not collapse to 1 MSS under 540 * adverse conditions. Implements RFC6582 541 */ 542 CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) + 543 CCV(ccv, t_maxseg); 544 else 545 /* Update cwnd based on beta and adjusted max_cwnd. */ 546 CCV(ccv, snd_cwnd) = max(((uint64_t)cubic_data->max_cwnd * 547 CUBIC_BETA) >> CUBIC_SHIFT, 548 2 * CCV(ccv, t_maxseg)); 549 } 550 551 /* Calculate the average RTT between congestion epochs. */ 552 if (cubic_data->epoch_ack_count > 0 && 553 cubic_data->sum_rtt_usecs >= cubic_data->epoch_ack_count) { 554 cubic_data->mean_rtt_usecs = (int)(cubic_data->sum_rtt_usecs / 555 cubic_data->epoch_ack_count); 556 } 557 558 cubic_data->epoch_ack_count = 0; 559 cubic_data->sum_rtt_usecs = 0; 560 } 561 562 /* 563 * Record the min RTT and sum samples for the epoch average RTT calculation. 564 */ 565 static void 566 cubic_record_rtt(struct cc_var *ccv) 567 { 568 struct cubic *cubic_data; 569 uint32_t t_srtt_usecs; 570 571 /* Ignore srtt until a min number of samples have been taken. */ 572 if (CCV(ccv, t_rttupdated) >= CUBIC_MIN_RTT_SAMPLES) { 573 cubic_data = ccv->cc_data; 574 t_srtt_usecs = tcp_get_srtt(ccv->ccvc.tcp, 575 TCP_TMR_GRANULARITY_USEC); 576 /* 577 * Record the current SRTT as our minrtt if it's the smallest 578 * we've seen or minrtt is currently equal to its initialised 579 * value. 580 * 581 * XXXLAS: Should there be some hysteresis for minrtt? 582 */ 583 if ((t_srtt_usecs < cubic_data->min_rtt_usecs || 584 cubic_data->min_rtt_usecs == TCPTV_SRTTBASE)) { 585 /* A minimal rtt is a single unshifted tick of a ticks 586 * timer. */ 587 cubic_data->min_rtt_usecs = max(tick >> TCP_RTT_SHIFT, 588 t_srtt_usecs); 589 590 /* 591 * If the connection is within its first congestion 592 * epoch, ensure we prime mean_rtt_usecs with a 593 * reasonable value until the epoch average RTT is 594 * calculated in cubic_post_recovery(). 595 */ 596 if (cubic_data->min_rtt_usecs > 597 cubic_data->mean_rtt_usecs) 598 cubic_data->mean_rtt_usecs = 599 cubic_data->min_rtt_usecs; 600 } 601 602 /* Sum samples for epoch average RTT calculation. */ 603 cubic_data->sum_rtt_usecs += t_srtt_usecs; 604 cubic_data->epoch_ack_count++; 605 } 606 } 607 608 /* 609 * Update the ssthresh in the event of congestion. 610 */ 611 static void 612 cubic_ssthresh_update(struct cc_var *ccv, uint32_t maxseg) 613 { 614 struct cubic *cubic_data; 615 uint32_t ssthresh; 616 uint32_t cwnd; 617 618 cubic_data = ccv->cc_data; 619 cwnd = CCV(ccv, snd_cwnd); 620 621 /* Fast convergence heuristic. */ 622 if (cwnd < cubic_data->max_cwnd) { 623 cwnd = ((uint64_t)cwnd * CUBIC_FC_FACTOR) >> CUBIC_SHIFT; 624 } 625 cubic_data->prev_max_cwnd = cubic_data->max_cwnd; 626 cubic_data->max_cwnd = cwnd; 627 628 /* 629 * On the first congestion event, set ssthresh to cwnd * 0.5 630 * and reduce max_cwnd to cwnd * beta. This aligns the cubic concave 631 * region appropriately. On subsequent congestion events, set 632 * ssthresh to cwnd * beta. 633 */ 634 if ((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) { 635 ssthresh = cwnd >> 1; 636 cubic_data->max_cwnd = ((uint64_t)cwnd * 637 CUBIC_BETA) >> CUBIC_SHIFT; 638 } else { 639 ssthresh = ((uint64_t)cwnd * 640 CUBIC_BETA) >> CUBIC_SHIFT; 641 } 642 CCV(ccv, snd_ssthresh) = max(ssthresh, 2 * maxseg); 643 } 644 645 static void 646 cubic_rttsample(struct cc_var *ccv, uint32_t usec_rtt, uint32_t rxtcnt, uint32_t fas) 647 { 648 struct cubic *cubicd; 649 650 cubicd = ccv->cc_data; 651 if (rxtcnt > 1) { 652 /* 653 * Only look at RTT's that are non-ambiguous. 654 */ 655 return; 656 } 657 cubicd->css_rttsample_count++; 658 cubicd->css_last_fas = fas; 659 if (cubicd->css_current_round_minrtt > usec_rtt) { 660 cubicd->css_current_round_minrtt = usec_rtt; 661 cubicd->css_lowrtt_fas = cubicd->css_last_fas; 662 } 663 if ((cubicd->css_rttsample_count >= hystart_n_rttsamples) && 664 (cubicd->css_current_round_minrtt != 0xffffffff) && 665 (cubicd->css_current_round_minrtt < cubicd->css_baseline_minrtt) && 666 (cubicd->css_lastround_minrtt != 0xffffffff)) { 667 /* 668 * We were in CSS and the RTT is now less, we 669 * entered CSS erroneously. 670 */ 671 cubicd->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 672 cubic_log_hystart_event(ccv, cubicd, 8, cubicd->css_baseline_minrtt); 673 cubicd->css_baseline_minrtt = 0xffffffff; 674 } 675 if (cubicd->flags & CUBICFLAG_HYSTART_ENABLED) 676 cubic_log_hystart_event(ccv, cubicd, 5, usec_rtt); 677 } 678 679 static void 680 cubic_newround(struct cc_var *ccv, uint32_t round_cnt) 681 { 682 struct cubic *cubicd; 683 684 cubicd = ccv->cc_data; 685 /* We have entered a new round */ 686 cubicd->css_lastround_minrtt = cubicd->css_current_round_minrtt; 687 cubicd->css_current_round_minrtt = 0xffffffff; 688 cubicd->css_rttsample_count = 0; 689 cubicd->css_current_round = round_cnt; 690 if ((cubicd->flags & CUBICFLAG_HYSTART_IN_CSS) && 691 ((round_cnt - cubicd->css_entered_at_round) >= hystart_css_rounds)) { 692 /* Enter CA */ 693 if (ccv->flags & CCF_HYSTART_CAN_SH_CWND) { 694 /* 695 * We engage more than snd_ssthresh, engage 696 * the brakes!! Though we will stay in SS to 697 * creep back up again, so lets leave CSS active 698 * and give us hystart_css_rounds more rounds. 699 */ 700 if (ccv->flags & CCF_HYSTART_CONS_SSTH) { 701 CCV(ccv, snd_ssthresh) = ((cubicd->css_lowrtt_fas + cubicd->css_fas_at_css_entry) / 2); 702 } else { 703 CCV(ccv, snd_ssthresh) = cubicd->css_lowrtt_fas; 704 } 705 CCV(ccv, snd_cwnd) = cubicd->css_fas_at_css_entry; 706 cubicd->css_entered_at_round = round_cnt; 707 } else { 708 CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd); 709 /* Turn off the CSS flag */ 710 cubicd->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 711 /* Disable use of CSS in the future except long idle */ 712 cubicd->flags &= ~CUBICFLAG_HYSTART_ENABLED; 713 } 714 cubic_log_hystart_event(ccv, cubicd, 6, CCV(ccv, snd_ssthresh)); 715 } 716 if (cubicd->flags & CUBICFLAG_HYSTART_ENABLED) 717 cubic_log_hystart_event(ccv, cubicd, 4, round_cnt); 718 } 719 720 DECLARE_CC_MODULE(cubic, &cubic_cc_algo); 721 MODULE_VERSION(cubic, 2); 722