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/param.h> 51#include <sys/kernel.h> 52#include <sys/limits.h> 53#include <sys/malloc.h> 54#include <sys/module.h> 55#include <sys/socket.h> 56#include <sys/socketvar.h> 57#include <sys/sysctl.h> 58#include <sys/systm.h> 59 60#include <net/vnet.h> 61 62#include <net/route.h> 63#include <net/route/nhop.h> 64 65#include <netinet/in_pcb.h> 66#include <netinet/tcp.h> 67#include <netinet/tcp_seq.h> 68#include <netinet/tcp_timer.h> 69#include <netinet/tcp_var.h> 70#include <netinet/tcp_log_buf.h> 71#include <netinet/tcp_hpts.h> 72#include <netinet/cc/cc.h> 73#include <netinet/cc/cc_cubic.h> 74#include <netinet/cc/cc_module.h> 75 76static void cubic_ack_received(struct cc_var *ccv, ccsignal_t type); 77static void cubic_cb_destroy(struct cc_var *ccv); 78static int cubic_cb_init(struct cc_var *ccv, void *ptr); 79static void cubic_cong_signal(struct cc_var *ccv, ccsignal_t type); 80static void cubic_conn_init(struct cc_var *ccv); 81static int cubic_mod_init(void); 82static void cubic_post_recovery(struct cc_var *ccv); 83static void cubic_record_rtt(struct cc_var *ccv); 84static void cubic_ssthresh_update(struct cc_var *ccv, uint32_t maxseg); 85static void cubic_after_idle(struct cc_var *ccv); 86static size_t cubic_data_sz(void); 87static void cubic_newround(struct cc_var *ccv, uint32_t round_cnt); 88static void cubic_rttsample(struct cc_var *ccv, uint32_t usec_rtt, 89 uint32_t rxtcnt, uint32_t fas); 90 91struct cc_algo cubic_cc_algo = { 92 .name = "cubic", 93 .ack_received = cubic_ack_received, 94 .cb_destroy = cubic_cb_destroy, 95 .cb_init = cubic_cb_init, 96 .cong_signal = cubic_cong_signal, 97 .conn_init = cubic_conn_init, 98 .mod_init = cubic_mod_init, 99 .post_recovery = cubic_post_recovery, 100 .after_idle = cubic_after_idle, 101 .cc_data_sz = cubic_data_sz, 102 .rttsample = cubic_rttsample, 103 .newround = cubic_newround 104}; 105 106static void 107cubic_log_hystart_event(struct cc_var *ccv, struct cubic *cubicd, uint8_t mod, uint32_t flex1) 108{ 109 /* 110 * Types of logs (mod value) 111 * 1 - rtt_thresh in flex1, checking to see if RTT is to great. 112 * 2 - rtt is too great, rtt_thresh in flex1. 113 * 3 - CSS is active incr in flex1 114 * 4 - A new round is beginning flex1 is round count 115 * 5 - A new RTT measurement flex1 is the new measurement. 116 * 6 - We enter CA ssthresh is also in flex1. 117 * 7 - Socket option to change hystart executed opt.val in flex1. 118 * 8 - Back out of CSS into SS, flex1 is the css_baseline_minrtt 119 * 9 - We enter CA, via an ECN mark. 120 * 10 - We enter CA, via a loss. 121 * 11 - We have slipped out of SS into CA via cwnd growth. 122 * 12 - After idle has re-enabled hystart++ 123 */ 124 struct tcpcb *tp; 125 126 if (hystart_bblogs == 0) 127 return; 128 tp = ccv->ccvc.tcp; 129 if (tcp_bblogging_on(tp)) { 130 union tcp_log_stackspecific log; 131 struct timeval tv; 132 133 memset(&log, 0, sizeof(log)); 134 log.u_bbr.flex1 = flex1; 135 log.u_bbr.flex2 = cubicd->css_current_round_minrtt; 136 log.u_bbr.flex3 = cubicd->css_lastround_minrtt; 137 log.u_bbr.flex4 = cubicd->css_rttsample_count; 138 log.u_bbr.flex5 = cubicd->css_entered_at_round; 139 log.u_bbr.flex6 = cubicd->css_baseline_minrtt; 140 /* We only need bottom 16 bits of flags */ 141 log.u_bbr.flex7 = cubicd->flags & 0x0000ffff; 142 log.u_bbr.flex8 = mod; 143 log.u_bbr.epoch = cubicd->css_current_round; 144 log.u_bbr.timeStamp = tcp_get_usecs(&tv); 145 log.u_bbr.lt_epoch = cubicd->css_fas_at_css_entry; 146 log.u_bbr.pkts_out = cubicd->css_last_fas; 147 log.u_bbr.delivered = cubicd->css_lowrtt_fas; 148 log.u_bbr.pkt_epoch = ccv->flags; 149 TCP_LOG_EVENTP(tp, NULL, 150 &tptosocket(tp)->so_rcv, 151 &tptosocket(tp)->so_snd, 152 TCP_HYSTART, 0, 153 0, &log, false, &tv); 154 } 155} 156 157static void 158cubic_does_slow_start(struct cc_var *ccv, struct cubic *cubicd) 159{ 160 /* 161 * In slow-start with ABC enabled and no RTO in sight? 162 * (Must not use abc_l_var > 1 if slow starting after 163 * an RTO. On RTO, snd_nxt = snd_una, so the 164 * snd_nxt == snd_max check is sufficient to 165 * handle this). 166 * 167 * XXXLAS: Find a way to signal SS after RTO that 168 * doesn't rely on tcpcb vars. 169 */ 170 u_int cw = CCV(ccv, snd_cwnd); 171 u_int incr = CCV(ccv, t_maxseg); 172 uint16_t abc_val; 173 174 cubicd->flags |= CUBICFLAG_IN_SLOWSTART; 175 if (ccv->flags & CCF_USE_LOCAL_ABC) 176 abc_val = ccv->labc; 177 else 178 abc_val = V_tcp_abc_l_var; 179 if ((ccv->flags & CCF_HYSTART_ALLOWED) && 180 (cubicd->flags & CUBICFLAG_HYSTART_ENABLED) && 181 ((cubicd->flags & CUBICFLAG_HYSTART_IN_CSS) == 0)) { 182 /* 183 * Hystart is allowed and still enabled and we are not yet 184 * in CSS. Lets check to see if we can make a decision on 185 * if we need to go into CSS. 186 */ 187 if ((cubicd->css_rttsample_count >= hystart_n_rttsamples) && 188 (cubicd->css_current_round_minrtt != 0xffffffff) && 189 (cubicd->css_lastround_minrtt != 0xffffffff)) { 190 uint32_t rtt_thresh; 191 192 /* Clamp (minrtt_thresh, lastround/8, maxrtt_thresh) */ 193 rtt_thresh = (cubicd->css_lastround_minrtt >> 3); 194 if (rtt_thresh < hystart_minrtt_thresh) 195 rtt_thresh = hystart_minrtt_thresh; 196 if (rtt_thresh > hystart_maxrtt_thresh) 197 rtt_thresh = hystart_maxrtt_thresh; 198 cubic_log_hystart_event(ccv, cubicd, 1, rtt_thresh); 199 200 if (cubicd->css_current_round_minrtt >= (cubicd->css_lastround_minrtt + rtt_thresh)) { 201 /* Enter CSS */ 202 cubicd->flags |= CUBICFLAG_HYSTART_IN_CSS; 203 cubicd->css_fas_at_css_entry = cubicd->css_lowrtt_fas; 204 /* 205 * The draft (v4) calls for us to set baseline to css_current_round_min 206 * but that can cause an oscillation. We probably shoudl be using 207 * css_lastround_minrtt, but the authors insist that will cause 208 * issues on exiting early. We will leave the draft version for now 209 * but I suspect this is incorrect. 210 */ 211 cubicd->css_baseline_minrtt = cubicd->css_current_round_minrtt; 212 cubicd->css_entered_at_round = cubicd->css_current_round; 213 cubic_log_hystart_event(ccv, cubicd, 2, rtt_thresh); 214 } 215 } 216 } 217 if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max)) 218 incr = min(ccv->bytes_this_ack, 219 ccv->nsegs * abc_val * 220 CCV(ccv, t_maxseg)); 221 else 222 incr = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg)); 223 224 /* Only if Hystart is enabled will the flag get set */ 225 if (cubicd->flags & CUBICFLAG_HYSTART_IN_CSS) { 226 incr /= hystart_css_growth_div; 227 cubic_log_hystart_event(ccv, cubicd, 3, incr); 228 } 229 /* ABC is on by default, so incr equals 0 frequently. */ 230 if (incr > 0) 231 CCV(ccv, snd_cwnd) = min((cw + incr), 232 TCP_MAXWIN << CCV(ccv, snd_scale)); 233} 234 235static void 236cubic_ack_received(struct cc_var *ccv, ccsignal_t type) 237{ 238 struct cubic *cubic_data; 239 unsigned long W_est, W_cubic; 240 int usecs_since_epoch; 241 242 cubic_data = ccv->cc_data; 243 cubic_record_rtt(ccv); 244 245 /* 246 * For a regular ACK and we're not in cong/fast recovery and 247 * we're cwnd limited, always recalculate cwnd. 248 */ 249 if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) && 250 (ccv->flags & CCF_CWND_LIMITED)) { 251 /* Use the logic in NewReno ack_received() for slow start. */ 252 if (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) || 253 cubic_data->min_rtt_usecs == TCPTV_SRTTBASE) { 254 cubic_does_slow_start(ccv, cubic_data); 255 } else { 256 if (cubic_data->flags & CUBICFLAG_HYSTART_IN_CSS) { 257 /* 258 * We have slipped into CA with 259 * CSS active. Deactivate all. 260 */ 261 /* Turn off the CSS flag */ 262 cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 263 /* Disable use of CSS in the future except long idle */ 264 cubic_data->flags &= ~CUBICFLAG_HYSTART_ENABLED; 265 cubic_log_hystart_event(ccv, cubic_data, 11, CCV(ccv, snd_ssthresh)); 266 } 267 if ((cubic_data->flags & CUBICFLAG_RTO_EVENT) && 268 (cubic_data->flags & CUBICFLAG_IN_SLOWSTART)) { 269 /* RFC8312 Section 4.7 */ 270 cubic_data->flags &= ~(CUBICFLAG_RTO_EVENT | 271 CUBICFLAG_IN_SLOWSTART); 272 cubic_data->W_max = CCV(ccv, snd_cwnd); 273 cubic_data->t_epoch = ticks; 274 cubic_data->K = 0; 275 } else if (cubic_data->flags & (CUBICFLAG_IN_SLOWSTART | 276 CUBICFLAG_IN_APPLIMIT)) { 277 cubic_data->flags &= ~(CUBICFLAG_IN_SLOWSTART | 278 CUBICFLAG_IN_APPLIMIT); 279 cubic_data->t_epoch = ticks; 280 cubic_data->K = cubic_k(cubic_data->W_max / 281 CCV(ccv, t_maxseg)); 282 } 283 usecs_since_epoch = (ticks - cubic_data->t_epoch) * tick; 284 if (usecs_since_epoch < 0) { 285 /* 286 * dragging t_epoch along 287 */ 288 usecs_since_epoch = INT_MAX; 289 cubic_data->t_epoch = ticks - INT_MAX; 290 } 291 /* 292 * The mean RTT is used to best reflect the equations in 293 * the I-D. Using min_rtt in the tf_cwnd calculation 294 * causes W_est to grow much faster than it should if the 295 * RTT is dominated by network buffering rather than 296 * propagation delay. 297 */ 298 W_est = tf_cwnd(usecs_since_epoch, cubic_data->mean_rtt_usecs, 299 cubic_data->W_max, CCV(ccv, t_maxseg)); 300 301 W_cubic = cubic_cwnd(usecs_since_epoch + 302 cubic_data->mean_rtt_usecs, 303 cubic_data->W_max, 304 CCV(ccv, t_maxseg), 305 cubic_data->K); 306 307 ccv->flags &= ~CCF_ABC_SENTAWND; 308 309 if (W_cubic < W_est) { 310 /* 311 * TCP-friendly region, follow tf 312 * cwnd growth. 313 */ 314 if (CCV(ccv, snd_cwnd) < W_est) 315 CCV(ccv, snd_cwnd) = ulmin(W_est, INT_MAX); 316 } else if (CCV(ccv, snd_cwnd) < W_cubic) { 317 /* 318 * Concave or convex region, follow CUBIC 319 * cwnd growth. 320 * Only update snd_cwnd, if it doesn't shrink. 321 */ 322 CCV(ccv, snd_cwnd) = ulmin(W_cubic, INT_MAX); 323 } 324 325 /* 326 * If we're not in slow start and we're probing for a 327 * new cwnd limit at the start of a connection 328 * (happens when hostcache has a relevant entry), 329 * keep updating our current estimate of the 330 * W_max. 331 */ 332 if (((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) && 333 cubic_data->W_max < CCV(ccv, snd_cwnd)) { 334 cubic_data->W_max = CCV(ccv, snd_cwnd); 335 cubic_data->K = cubic_k(cubic_data->W_max / 336 CCV(ccv, t_maxseg)); 337 } 338 } 339 } else if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) && 340 !(ccv->flags & CCF_CWND_LIMITED)) { 341 cubic_data->flags |= CUBICFLAG_IN_APPLIMIT; 342 } 343} 344 345/* 346 * This is a CUBIC specific implementation of after_idle. 347 * - Reset cwnd by calling New Reno implementation of after_idle. 348 * - Reset t_epoch. 349 */ 350static void 351cubic_after_idle(struct cc_var *ccv) 352{ 353 struct cubic *cubic_data; 354 355 cubic_data = ccv->cc_data; 356 357 cubic_data->W_max = ulmax(cubic_data->W_max, CCV(ccv, snd_cwnd)); 358 cubic_data->K = cubic_k(cubic_data->W_max / CCV(ccv, t_maxseg)); 359 if ((cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) == 0) { 360 /* 361 * Re-enable hystart if we have been idle. 362 */ 363 cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 364 cubic_data->flags |= CUBICFLAG_HYSTART_ENABLED; 365 cubic_log_hystart_event(ccv, cubic_data, 12, CCV(ccv, snd_ssthresh)); 366 } 367 newreno_cc_after_idle(ccv); 368 cubic_data->t_epoch = ticks; 369} 370 371static void 372cubic_cb_destroy(struct cc_var *ccv) 373{ 374 free(ccv->cc_data, M_CC_MEM); 375} 376 377static size_t 378cubic_data_sz(void) 379{ 380 return (sizeof(struct cubic)); 381} 382 383static int 384cubic_cb_init(struct cc_var *ccv, void *ptr) 385{ 386 struct cubic *cubic_data; 387 388 INP_WLOCK_ASSERT(tptoinpcb(ccv->ccvc.tcp)); 389 if (ptr == NULL) { 390 cubic_data = malloc(sizeof(struct cubic), M_CC_MEM, M_NOWAIT|M_ZERO); 391 if (cubic_data == NULL) 392 return (ENOMEM); 393 } else 394 cubic_data = ptr; 395 396 /* Init some key variables with sensible defaults. */ 397 cubic_data->t_epoch = ticks; 398 cubic_data->min_rtt_usecs = TCPTV_SRTTBASE; 399 cubic_data->mean_rtt_usecs = 1; 400 401 ccv->cc_data = cubic_data; 402 cubic_data->flags = CUBICFLAG_HYSTART_ENABLED; 403 /* At init set both to infinity */ 404 cubic_data->css_lastround_minrtt = 0xffffffff; 405 cubic_data->css_current_round_minrtt = 0xffffffff; 406 cubic_data->css_current_round = 0; 407 cubic_data->css_baseline_minrtt = 0xffffffff; 408 cubic_data->css_rttsample_count = 0; 409 cubic_data->css_entered_at_round = 0; 410 cubic_data->css_fas_at_css_entry = 0; 411 cubic_data->css_lowrtt_fas = 0; 412 cubic_data->css_last_fas = 0; 413 414 return (0); 415} 416 417/* 418 * Perform any necessary tasks before we enter congestion recovery. 419 */ 420static void 421cubic_cong_signal(struct cc_var *ccv, ccsignal_t type) 422{ 423 struct cubic *cubic_data; 424 uint32_t mss, pipe; 425 426 cubic_data = ccv->cc_data; 427 mss = tcp_fixed_maxseg(ccv->ccvc.tcp); 428 429 switch (type) { 430 case CC_NDUPACK: 431 if (cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) { 432 /* Make sure the flags are all off we had a loss */ 433 cubic_data->flags &= ~CUBICFLAG_HYSTART_ENABLED; 434 cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 435 cubic_log_hystart_event(ccv, cubic_data, 10, CCV(ccv, snd_ssthresh)); 436 } 437 if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) { 438 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { 439 cubic_ssthresh_update(ccv, mss); 440 cubic_data->flags |= CUBICFLAG_CONG_EVENT; 441 cubic_data->t_epoch = ticks; 442 cubic_data->K = cubic_k(cubic_data->W_max / mss); 443 } 444 ENTER_RECOVERY(CCV(ccv, t_flags)); 445 } 446 break; 447 448 case CC_ECN: 449 if (cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) { 450 /* Make sure the flags are all off we had a loss */ 451 cubic_data->flags &= ~CUBICFLAG_HYSTART_ENABLED; 452 cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 453 cubic_log_hystart_event(ccv, cubic_data, 9, CCV(ccv, snd_ssthresh)); 454 } 455 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { 456 cubic_ssthresh_update(ccv, mss); 457 cubic_data->flags |= CUBICFLAG_CONG_EVENT; 458 cubic_data->t_epoch = ticks; 459 cubic_data->K = cubic_k(cubic_data->W_max / mss); 460 CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh); 461 ENTER_CONGRECOVERY(CCV(ccv, t_flags)); 462 } 463 break; 464 465 case CC_RTO: 466 /* RFC8312 Section 4.7 */ 467 if (CCV(ccv, t_rxtshift) == 1) { 468 /* 469 * Remember the state only for the first RTO event. This 470 * will help us restore the state to the values seen 471 * at the most recent congestion avoidance stage before 472 * the current RTO event. 473 */ 474 cubic_data->undo_t_epoch = cubic_data->t_epoch; 475 cubic_data->undo_cwnd_epoch = cubic_data->cwnd_epoch; 476 cubic_data->undo_W_est = cubic_data->W_est; 477 cubic_data->undo_cwnd_prior = cubic_data->cwnd_prior; 478 cubic_data->undo_W_max = cubic_data->W_max; 479 cubic_data->undo_K = cubic_data->K; 480 if (V_tcp_do_newsack) { 481 pipe = tcp_compute_pipe(ccv->ccvc.tcp); 482 } else { 483 pipe = CCV(ccv, snd_max) - 484 CCV(ccv, snd_fack) + 485 CCV(ccv, sackhint.sack_bytes_rexmit); 486 } 487 CCV(ccv, snd_ssthresh) = max(2, 488 (((uint64_t)min(CCV(ccv, snd_wnd), pipe) * 489 CUBIC_BETA) >> CUBIC_SHIFT) / mss) * mss; 490 } 491 cubic_data->flags |= CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT; 492 cubic_data->undo_W_max = cubic_data->W_max; 493 cubic_data->num_cong_events++; 494 CCV(ccv, snd_cwnd) = mss; 495 break; 496 497 case CC_RTO_ERR: 498 cubic_data->flags &= ~(CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT); 499 cubic_data->num_cong_events--; 500 cubic_data->K = cubic_data->undo_K; 501 cubic_data->cwnd_prior = cubic_data->undo_cwnd_prior; 502 cubic_data->W_max = cubic_data->undo_W_max; 503 cubic_data->W_est = cubic_data->undo_W_est; 504 cubic_data->cwnd_epoch = cubic_data->undo_cwnd_epoch; 505 cubic_data->t_epoch = cubic_data->undo_t_epoch; 506 break; 507 default: 508 break; 509 } 510} 511 512static void 513cubic_conn_init(struct cc_var *ccv) 514{ 515 struct cubic *cubic_data; 516 517 cubic_data = ccv->cc_data; 518 519 /* 520 * Ensure we have a sane initial value for W_max recorded. Without 521 * this here bad things happen when entries from the TCP hostcache 522 * get used. 523 */ 524 cubic_data->W_max = CCV(ccv, snd_cwnd); 525} 526 527static int 528cubic_mod_init(void) 529{ 530 return (0); 531} 532 533/* 534 * Perform any necessary tasks before we exit congestion recovery. 535 */ 536static void 537cubic_post_recovery(struct cc_var *ccv) 538{ 539 struct cubic *cubic_data; 540 int pipe; 541 542 cubic_data = ccv->cc_data; 543 pipe = 0; 544 545 if (IN_FASTRECOVERY(CCV(ccv, t_flags))) { 546 /* 547 * If inflight data is less than ssthresh, set cwnd 548 * conservatively to avoid a burst of data, as suggested in 549 * the NewReno RFC. Otherwise, use the CUBIC method. 550 * 551 * XXXLAS: Find a way to do this without needing curack 552 */ 553 if (V_tcp_do_newsack) 554 pipe = tcp_compute_pipe(ccv->ccvc.tcp); 555 else 556 pipe = CCV(ccv, snd_max) - ccv->curack; 557 558 if (pipe < CCV(ccv, snd_ssthresh)) 559 /* 560 * Ensure that cwnd does not collapse to 1 MSS under 561 * adverse conditions. Implements RFC6582 562 */ 563 CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) + 564 CCV(ccv, t_maxseg); 565 else 566 /* Update cwnd based on beta and adjusted W_max. */ 567 CCV(ccv, snd_cwnd) = max(((uint64_t)cubic_data->W_max * 568 CUBIC_BETA) >> CUBIC_SHIFT, 569 2 * CCV(ccv, t_maxseg)); 570 } 571 572 /* Calculate the average RTT between congestion epochs. */ 573 if (cubic_data->epoch_ack_count > 0 && 574 cubic_data->sum_rtt_usecs >= cubic_data->epoch_ack_count) { 575 cubic_data->mean_rtt_usecs = (int)(cubic_data->sum_rtt_usecs / 576 cubic_data->epoch_ack_count); 577 } 578 579 cubic_data->epoch_ack_count = 0; 580 cubic_data->sum_rtt_usecs = 0; 581} 582 583/* 584 * Record the min RTT and sum samples for the epoch average RTT calculation. 585 */ 586static void 587cubic_record_rtt(struct cc_var *ccv) 588{ 589 struct cubic *cubic_data; 590 uint32_t t_srtt_usecs; 591 592 /* Ignore srtt until a min number of samples have been taken. */ 593 if (CCV(ccv, t_rttupdated) >= CUBIC_MIN_RTT_SAMPLES) { 594 cubic_data = ccv->cc_data; 595 t_srtt_usecs = tcp_get_srtt(ccv->ccvc.tcp, 596 TCP_TMR_GRANULARITY_USEC); 597 /* 598 * Record the current SRTT as our minrtt if it's the smallest 599 * we've seen or minrtt is currently equal to its initialised 600 * value. 601 * 602 * XXXLAS: Should there be some hysteresis for minrtt? 603 */ 604 if ((t_srtt_usecs < cubic_data->min_rtt_usecs || 605 cubic_data->min_rtt_usecs == TCPTV_SRTTBASE)) { 606 /* A minimal rtt is a single unshifted tick of a ticks 607 * timer. */ 608 cubic_data->min_rtt_usecs = max(tick >> TCP_RTT_SHIFT, 609 t_srtt_usecs); 610 611 /* 612 * If the connection is within its first congestion 613 * epoch, ensure we prime mean_rtt_usecs with a 614 * reasonable value until the epoch average RTT is 615 * calculated in cubic_post_recovery(). 616 */ 617 if (cubic_data->min_rtt_usecs > 618 cubic_data->mean_rtt_usecs) 619 cubic_data->mean_rtt_usecs = 620 cubic_data->min_rtt_usecs; 621 } 622 623 /* Sum samples for epoch average RTT calculation. */ 624 cubic_data->sum_rtt_usecs += t_srtt_usecs; 625 cubic_data->epoch_ack_count++; 626 } 627} 628 629/* 630 * Update the ssthresh in the event of congestion. 631 */ 632static void 633cubic_ssthresh_update(struct cc_var *ccv, uint32_t maxseg) 634{ 635 struct cubic *cubic_data; 636 uint32_t ssthresh; 637 uint32_t cwnd; 638 639 cubic_data = ccv->cc_data; 640 cwnd = CCV(ccv, snd_cwnd); 641 642 /* Fast convergence heuristic. */ 643 if (cwnd < cubic_data->W_max) { 644 cwnd = ((uint64_t)cwnd * CUBIC_FC_FACTOR) >> CUBIC_SHIFT; 645 } 646 cubic_data->undo_W_max = cubic_data->W_max; 647 cubic_data->W_max = cwnd; 648 649 /* 650 * On the first congestion event, set ssthresh to cwnd * 0.5 651 * and reduce W_max to cwnd * beta. This aligns the cubic concave 652 * region appropriately. On subsequent congestion events, set 653 * ssthresh to cwnd * beta. 654 */ 655 if ((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) { 656 ssthresh = cwnd >> 1; 657 cubic_data->W_max = ((uint64_t)cwnd * 658 CUBIC_BETA) >> CUBIC_SHIFT; 659 } else { 660 ssthresh = ((uint64_t)cwnd * 661 CUBIC_BETA) >> CUBIC_SHIFT; 662 } 663 CCV(ccv, snd_ssthresh) = max(ssthresh, 2 * maxseg); 664} 665 666static void 667cubic_rttsample(struct cc_var *ccv, uint32_t usec_rtt, uint32_t rxtcnt, uint32_t fas) 668{ 669 struct cubic *cubicd; 670 671 cubicd = ccv->cc_data; 672 if (rxtcnt > 1) { 673 /* 674 * Only look at RTT's that are non-ambiguous. 675 */ 676 return; 677 } 678 cubicd->css_rttsample_count++; 679 cubicd->css_last_fas = fas; 680 if (cubicd->css_current_round_minrtt > usec_rtt) { 681 cubicd->css_current_round_minrtt = usec_rtt; 682 cubicd->css_lowrtt_fas = cubicd->css_last_fas; 683 } 684 if ((cubicd->css_rttsample_count >= hystart_n_rttsamples) && 685 (cubicd->css_current_round_minrtt != 0xffffffff) && 686 (cubicd->css_current_round_minrtt < cubicd->css_baseline_minrtt) && 687 (cubicd->css_lastround_minrtt != 0xffffffff)) { 688 /* 689 * We were in CSS and the RTT is now less, we 690 * entered CSS erroneously. 691 */ 692 cubicd->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 693 cubic_log_hystart_event(ccv, cubicd, 8, cubicd->css_baseline_minrtt); 694 cubicd->css_baseline_minrtt = 0xffffffff; 695 } 696 if (cubicd->flags & CUBICFLAG_HYSTART_ENABLED) 697 cubic_log_hystart_event(ccv, cubicd, 5, usec_rtt); 698} 699 700static void 701cubic_newround(struct cc_var *ccv, uint32_t round_cnt) 702{ 703 struct cubic *cubicd; 704 705 cubicd = ccv->cc_data; 706 /* We have entered a new round */ 707 cubicd->css_lastround_minrtt = cubicd->css_current_round_minrtt; 708 cubicd->css_current_round_minrtt = 0xffffffff; 709 cubicd->css_rttsample_count = 0; 710 cubicd->css_current_round = round_cnt; 711 if ((cubicd->flags & CUBICFLAG_HYSTART_IN_CSS) && 712 ((round_cnt - cubicd->css_entered_at_round) >= hystart_css_rounds)) { 713 /* Enter CA */ 714 if (ccv->flags & CCF_HYSTART_CAN_SH_CWND) { 715 /* 716 * We engage more than snd_ssthresh, engage 717 * the brakes!! Though we will stay in SS to 718 * creep back up again, so lets leave CSS active 719 * and give us hystart_css_rounds more rounds. 720 */ 721 if (ccv->flags & CCF_HYSTART_CONS_SSTH) { 722 CCV(ccv, snd_ssthresh) = ((cubicd->css_lowrtt_fas + cubicd->css_fas_at_css_entry) / 2); 723 } else { 724 CCV(ccv, snd_ssthresh) = cubicd->css_lowrtt_fas; 725 } 726 CCV(ccv, snd_cwnd) = cubicd->css_fas_at_css_entry; 727 cubicd->css_entered_at_round = round_cnt; 728 } else { 729 CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd); 730 /* Turn off the CSS flag */ 731 cubicd->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 732 /* Disable use of CSS in the future except long idle */ 733 cubicd->flags &= ~CUBICFLAG_HYSTART_ENABLED; 734 } 735 cubic_log_hystart_event(ccv, cubicd, 6, CCV(ccv, snd_ssthresh)); 736 } 737 if (cubicd->flags & CUBICFLAG_HYSTART_ENABLED) 738 cubic_log_hystart_event(ccv, cubicd, 4, round_cnt); 739} 740 741DECLARE_CC_MODULE(cubic, &cubic_cc_algo); 742MODULE_VERSION(cubic, 2); 743