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 76 static void cubic_ack_received(struct cc_var *ccv, ccsignal_t type); 77 static void cubic_cb_destroy(struct cc_var *ccv); 78 static int cubic_cb_init(struct cc_var *ccv, void *ptr); 79 static void cubic_cong_signal(struct cc_var *ccv, ccsignal_t type); 80 static void cubic_conn_init(struct cc_var *ccv); 81 static int cubic_mod_init(void); 82 static void cubic_post_recovery(struct cc_var *ccv); 83 static void cubic_record_rtt(struct cc_var *ccv); 84 static void cubic_ssthresh_update(struct cc_var *ccv, uint32_t maxseg); 85 static void cubic_after_idle(struct cc_var *ccv); 86 static size_t cubic_data_sz(void); 87 static void cubic_newround(struct cc_var *ccv, uint32_t round_cnt); 88 static void cubic_rttsample(struct cc_var *ccv, uint32_t usec_rtt, 89 uint32_t rxtcnt, uint32_t fas); 90 91 struct 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 }; 105 106 static void 107 cubic_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->tp; 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 } 156 157 static void 158 cubic_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 } 234 235 static void 236 cubic_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 W_est = tf_cwnd(ccv); 293 294 /* 295 * The mean RTT is used to best reflect the equations in 296 * the I-D. 297 */ 298 W_cubic = cubic_cwnd(usecs_since_epoch + 299 cubic_data->mean_rtt_usecs, 300 cubic_data->W_max, 301 CCV(ccv, t_maxseg), 302 cubic_data->K); 303 304 if (W_cubic < W_est) { 305 /* 306 * TCP-friendly region, follow tf 307 * cwnd growth. 308 */ 309 CCV(ccv, snd_cwnd) = ulmin(W_est, INT_MAX); 310 cubic_data->flags |= CUBICFLAG_IN_TF; 311 } else if (CCV(ccv, snd_cwnd) < W_cubic) { 312 /* 313 * Concave or convex region, follow CUBIC 314 * cwnd growth. 315 * Only update snd_cwnd, if it doesn't shrink. 316 */ 317 CCV(ccv, snd_cwnd) = ulmin(W_cubic, INT_MAX); 318 cubic_data->flags &= ~CUBICFLAG_IN_TF; 319 } 320 321 /* 322 * If we're not in slow start and we're probing for a 323 * new cwnd limit at the start of a connection 324 * (happens when hostcache has a relevant entry), 325 * keep updating our current estimate of the 326 * W_max. 327 */ 328 if (((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) && 329 cubic_data->W_max < CCV(ccv, snd_cwnd)) { 330 cubic_data->W_max = CCV(ccv, snd_cwnd); 331 cubic_data->K = cubic_k(cubic_data->W_max / 332 CCV(ccv, t_maxseg)); 333 } 334 } 335 } else if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) && 336 !(ccv->flags & CCF_CWND_LIMITED)) { 337 cubic_data->flags |= CUBICFLAG_IN_APPLIMIT; 338 } 339 } 340 341 /* 342 * This is a CUBIC specific implementation of after_idle. 343 * - Reset cwnd by calling New Reno implementation of after_idle. 344 * - Reset t_epoch. 345 */ 346 static void 347 cubic_after_idle(struct cc_var *ccv) 348 { 349 struct cubic *cubic_data; 350 351 cubic_data = ccv->cc_data; 352 353 cubic_data->W_max = ulmax(cubic_data->W_max, CCV(ccv, snd_cwnd)); 354 cubic_data->K = cubic_k(cubic_data->W_max / CCV(ccv, t_maxseg)); 355 if ((cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) == 0) { 356 /* 357 * Re-enable hystart if we have been idle. 358 */ 359 cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 360 cubic_data->flags |= CUBICFLAG_HYSTART_ENABLED; 361 cubic_log_hystart_event(ccv, cubic_data, 12, CCV(ccv, snd_ssthresh)); 362 } 363 newreno_cc_after_idle(ccv); 364 cubic_data->t_epoch = ticks; 365 } 366 367 static void 368 cubic_cb_destroy(struct cc_var *ccv) 369 { 370 free(ccv->cc_data, M_CC_MEM); 371 } 372 373 static size_t 374 cubic_data_sz(void) 375 { 376 return (sizeof(struct cubic)); 377 } 378 379 static int 380 cubic_cb_init(struct cc_var *ccv, void *ptr) 381 { 382 struct cubic *cubic_data; 383 384 INP_WLOCK_ASSERT(tptoinpcb(ccv->tp)); 385 if (ptr == NULL) { 386 cubic_data = malloc(sizeof(struct cubic), M_CC_MEM, M_NOWAIT|M_ZERO); 387 if (cubic_data == NULL) 388 return (ENOMEM); 389 } else 390 cubic_data = ptr; 391 392 /* Init some key variables with sensible defaults. */ 393 cubic_data->t_epoch = ticks; 394 cubic_data->min_rtt_usecs = TCPTV_SRTTBASE; 395 cubic_data->mean_rtt_usecs = 1; 396 397 ccv->cc_data = cubic_data; 398 cubic_data->flags = CUBICFLAG_HYSTART_ENABLED; 399 /* At init set both to infinity */ 400 cubic_data->css_lastround_minrtt = 0xffffffff; 401 cubic_data->css_current_round_minrtt = 0xffffffff; 402 cubic_data->css_current_round = 0; 403 cubic_data->css_baseline_minrtt = 0xffffffff; 404 cubic_data->css_rttsample_count = 0; 405 cubic_data->css_entered_at_round = 0; 406 cubic_data->css_fas_at_css_entry = 0; 407 cubic_data->css_lowrtt_fas = 0; 408 cubic_data->css_last_fas = 0; 409 410 return (0); 411 } 412 413 /* 414 * Perform any necessary tasks before we enter congestion recovery. 415 */ 416 static void 417 cubic_cong_signal(struct cc_var *ccv, ccsignal_t type) 418 { 419 struct cubic *cubic_data; 420 uint32_t mss, pipe; 421 422 cubic_data = ccv->cc_data; 423 mss = tcp_fixed_maxseg(ccv->tp); 424 425 switch (type) { 426 case CC_NDUPACK: 427 if (cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) { 428 /* Make sure the flags are all off we had a loss */ 429 cubic_data->flags &= ~CUBICFLAG_HYSTART_ENABLED; 430 cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 431 cubic_log_hystart_event(ccv, cubic_data, 10, CCV(ccv, snd_ssthresh)); 432 } 433 if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) { 434 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { 435 cubic_ssthresh_update(ccv, mss); 436 cubic_data->flags |= CUBICFLAG_CONG_EVENT; 437 cubic_data->t_epoch = ticks; 438 cubic_data->K = cubic_k(cubic_data->W_max / mss); 439 } 440 ENTER_RECOVERY(CCV(ccv, t_flags)); 441 } 442 break; 443 444 case CC_ECN: 445 if (cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) { 446 /* Make sure the flags are all off we had a loss */ 447 cubic_data->flags &= ~CUBICFLAG_HYSTART_ENABLED; 448 cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 449 cubic_log_hystart_event(ccv, cubic_data, 9, CCV(ccv, snd_ssthresh)); 450 } 451 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { 452 cubic_ssthresh_update(ccv, mss); 453 cubic_data->flags |= CUBICFLAG_CONG_EVENT; 454 cubic_data->t_epoch = ticks; 455 cubic_data->K = cubic_k(cubic_data->W_max / mss); 456 CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh); 457 ENTER_CONGRECOVERY(CCV(ccv, t_flags)); 458 } 459 break; 460 461 case CC_RTO: 462 /* RFC8312 Section 4.7 */ 463 if (CCV(ccv, t_rxtshift) == 1) { 464 /* 465 * Remember the state only for the first RTO event. This 466 * will help us restore the state to the values seen 467 * at the most recent congestion avoidance stage before 468 * the current RTO event. 469 */ 470 cubic_data->undo_t_epoch = cubic_data->t_epoch; 471 cubic_data->undo_cwnd_epoch = cubic_data->cwnd_epoch; 472 cubic_data->undo_W_est = cubic_data->W_est; 473 cubic_data->undo_cwnd_prior = cubic_data->cwnd_prior; 474 cubic_data->undo_W_max = cubic_data->W_max; 475 cubic_data->undo_K = cubic_data->K; 476 if (V_tcp_do_newsack) { 477 pipe = tcp_compute_pipe(ccv->tp); 478 } else { 479 pipe = CCV(ccv, snd_max) - 480 CCV(ccv, snd_fack) + 481 CCV(ccv, sackhint.sack_bytes_rexmit); 482 } 483 CCV(ccv, snd_ssthresh) = max(2, 484 (((uint64_t)min(CCV(ccv, snd_wnd), pipe) * 485 CUBIC_BETA) >> CUBIC_SHIFT) / mss) * mss; 486 } 487 cubic_data->flags |= CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT; 488 cubic_data->undo_W_max = cubic_data->W_max; 489 CCV(ccv, snd_cwnd) = mss; 490 break; 491 492 case CC_RTO_ERR: 493 cubic_data->flags &= ~(CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT); 494 cubic_data->K = cubic_data->undo_K; 495 cubic_data->cwnd_prior = cubic_data->undo_cwnd_prior; 496 cubic_data->W_max = cubic_data->undo_W_max; 497 cubic_data->W_est = cubic_data->undo_W_est; 498 cubic_data->cwnd_epoch = cubic_data->undo_cwnd_epoch; 499 cubic_data->t_epoch = cubic_data->undo_t_epoch; 500 break; 501 default: 502 break; 503 } 504 } 505 506 static void 507 cubic_conn_init(struct cc_var *ccv) 508 { 509 struct cubic *cubic_data; 510 511 cubic_data = ccv->cc_data; 512 513 /* 514 * Ensure we have a sane initial value for W_max recorded. Without 515 * this here bad things happen when entries from the TCP hostcache 516 * get used. 517 */ 518 cubic_data->W_max = CCV(ccv, snd_cwnd); 519 } 520 521 static int 522 cubic_mod_init(void) 523 { 524 return (0); 525 } 526 527 /* 528 * Perform any necessary tasks before we exit congestion recovery. 529 */ 530 static void 531 cubic_post_recovery(struct cc_var *ccv) 532 { 533 struct cubic *cubic_data; 534 int pipe; 535 536 cubic_data = ccv->cc_data; 537 pipe = 0; 538 539 if (IN_FASTRECOVERY(CCV(ccv, t_flags))) { 540 /* 541 * If inflight data is less than ssthresh, set cwnd 542 * conservatively to avoid a burst of data, as suggested in 543 * the NewReno RFC. Otherwise, use the CUBIC method. 544 * 545 * XXXLAS: Find a way to do this without needing curack 546 */ 547 if (V_tcp_do_newsack) 548 pipe = tcp_compute_pipe(ccv->tp); 549 else 550 pipe = CCV(ccv, snd_max) - ccv->curack; 551 552 if (pipe < CCV(ccv, snd_ssthresh)) 553 /* 554 * Ensure that cwnd does not collapse to 1 MSS under 555 * adverse conditions. Implements RFC6582 556 */ 557 CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) + 558 CCV(ccv, t_maxseg); 559 else 560 /* Update cwnd based on beta and adjusted W_max. */ 561 CCV(ccv, snd_cwnd) = max(((uint64_t)cubic_data->W_max * 562 CUBIC_BETA) >> CUBIC_SHIFT, 563 2 * CCV(ccv, t_maxseg)); 564 } 565 566 /* Calculate the average RTT between congestion epochs. */ 567 if (cubic_data->epoch_ack_count > 0 && 568 cubic_data->sum_rtt_usecs >= cubic_data->epoch_ack_count) { 569 cubic_data->mean_rtt_usecs = (int)(cubic_data->sum_rtt_usecs / 570 cubic_data->epoch_ack_count); 571 } 572 573 cubic_data->epoch_ack_count = 0; 574 cubic_data->sum_rtt_usecs = 0; 575 } 576 577 /* 578 * Record the min RTT and sum samples for the epoch average RTT calculation. 579 */ 580 static void 581 cubic_record_rtt(struct cc_var *ccv) 582 { 583 struct cubic *cubic_data; 584 uint32_t t_srtt_usecs; 585 586 /* Ignore srtt until a min number of samples have been taken. */ 587 if (CCV(ccv, t_rttupdated) >= CUBIC_MIN_RTT_SAMPLES) { 588 cubic_data = ccv->cc_data; 589 t_srtt_usecs = tcp_get_srtt(ccv->tp, 590 TCP_TMR_GRANULARITY_USEC); 591 /* 592 * Record the current SRTT as our minrtt if it's the smallest 593 * we've seen or minrtt is currently equal to its initialised 594 * value. 595 * 596 * XXXLAS: Should there be some hysteresis for minrtt? 597 */ 598 if ((t_srtt_usecs < cubic_data->min_rtt_usecs || 599 cubic_data->min_rtt_usecs == TCPTV_SRTTBASE)) { 600 /* A minimal rtt is a single unshifted tick of a ticks 601 * timer. */ 602 cubic_data->min_rtt_usecs = max(tick >> TCP_RTT_SHIFT, 603 t_srtt_usecs); 604 605 /* 606 * If the connection is within its first congestion 607 * epoch, ensure we prime mean_rtt_usecs with a 608 * reasonable value until the epoch average RTT is 609 * calculated in cubic_post_recovery(). 610 */ 611 if (cubic_data->min_rtt_usecs > 612 cubic_data->mean_rtt_usecs) 613 cubic_data->mean_rtt_usecs = 614 cubic_data->min_rtt_usecs; 615 } 616 617 /* Sum samples for epoch average RTT calculation. */ 618 cubic_data->sum_rtt_usecs += t_srtt_usecs; 619 cubic_data->epoch_ack_count++; 620 } 621 } 622 623 /* 624 * Update the ssthresh in the event of congestion. 625 */ 626 static void 627 cubic_ssthresh_update(struct cc_var *ccv, uint32_t maxseg) 628 { 629 struct cubic *cubic_data; 630 uint32_t ssthresh; 631 uint32_t cwnd; 632 633 cubic_data = ccv->cc_data; 634 cwnd = CCV(ccv, snd_cwnd); 635 636 /* Fast convergence heuristic. */ 637 if (cwnd < cubic_data->W_max) { 638 cwnd = ((uint64_t)cwnd * CUBIC_FC_FACTOR) >> CUBIC_SHIFT; 639 } 640 cubic_data->undo_W_max = cubic_data->W_max; 641 cubic_data->W_max = cwnd; 642 643 if (cubic_data->flags & CUBICFLAG_IN_TF) { 644 /* If in the TCP friendly region, follow what newreno does */ 645 ssthresh = newreno_cc_cwnd_on_multiplicative_decrease(ccv, maxseg); 646 647 } else if ((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) { 648 /* 649 * On the first congestion event, set ssthresh to cwnd * 0.5 650 * and reduce W_max to cwnd * beta. This aligns the cubic 651 * concave region appropriately. 652 */ 653 ssthresh = cwnd >> 1; 654 cubic_data->W_max = ((uint64_t)cwnd * CUBIC_BETA) >> CUBIC_SHIFT; 655 } else { 656 /* 657 * On subsequent congestion events, set ssthresh to cwnd * beta. 658 */ 659 ssthresh = ((uint64_t)cwnd * CUBIC_BETA) >> CUBIC_SHIFT; 660 } 661 CCV(ccv, snd_ssthresh) = max(ssthresh, 2 * maxseg); 662 } 663 664 static void 665 cubic_rttsample(struct cc_var *ccv, uint32_t usec_rtt, uint32_t rxtcnt, uint32_t fas) 666 { 667 struct cubic *cubicd; 668 669 cubicd = ccv->cc_data; 670 if (rxtcnt > 1) { 671 /* 672 * Only look at RTT's that are non-ambiguous. 673 */ 674 return; 675 } 676 cubicd->css_rttsample_count++; 677 cubicd->css_last_fas = fas; 678 if (cubicd->css_current_round_minrtt > usec_rtt) { 679 cubicd->css_current_round_minrtt = usec_rtt; 680 cubicd->css_lowrtt_fas = cubicd->css_last_fas; 681 } 682 if ((cubicd->css_rttsample_count >= hystart_n_rttsamples) && 683 (cubicd->css_current_round_minrtt != 0xffffffff) && 684 (cubicd->css_current_round_minrtt < cubicd->css_baseline_minrtt) && 685 (cubicd->css_lastround_minrtt != 0xffffffff)) { 686 /* 687 * We were in CSS and the RTT is now less, we 688 * entered CSS erroneously. 689 */ 690 cubicd->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 691 cubic_log_hystart_event(ccv, cubicd, 8, cubicd->css_baseline_minrtt); 692 cubicd->css_baseline_minrtt = 0xffffffff; 693 } 694 if (cubicd->flags & CUBICFLAG_HYSTART_ENABLED) 695 cubic_log_hystart_event(ccv, cubicd, 5, usec_rtt); 696 } 697 698 static void 699 cubic_newround(struct cc_var *ccv, uint32_t round_cnt) 700 { 701 struct cubic *cubicd; 702 703 cubicd = ccv->cc_data; 704 /* We have entered a new round */ 705 cubicd->css_lastround_minrtt = cubicd->css_current_round_minrtt; 706 cubicd->css_current_round_minrtt = 0xffffffff; 707 cubicd->css_rttsample_count = 0; 708 cubicd->css_current_round = round_cnt; 709 if ((cubicd->flags & CUBICFLAG_HYSTART_IN_CSS) && 710 ((round_cnt - cubicd->css_entered_at_round) >= hystart_css_rounds)) { 711 /* Enter CA */ 712 if (ccv->flags & CCF_HYSTART_CAN_SH_CWND) { 713 /* 714 * We engage more than snd_ssthresh, engage 715 * the brakes!! Though we will stay in SS to 716 * creep back up again, so lets leave CSS active 717 * and give us hystart_css_rounds more rounds. 718 */ 719 if (ccv->flags & CCF_HYSTART_CONS_SSTH) { 720 CCV(ccv, snd_ssthresh) = ((cubicd->css_lowrtt_fas + cubicd->css_fas_at_css_entry) / 2); 721 } else { 722 CCV(ccv, snd_ssthresh) = cubicd->css_lowrtt_fas; 723 } 724 CCV(ccv, snd_cwnd) = cubicd->css_fas_at_css_entry; 725 cubicd->css_entered_at_round = round_cnt; 726 } else { 727 CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd); 728 /* Turn off the CSS flag */ 729 cubicd->flags &= ~CUBICFLAG_HYSTART_IN_CSS; 730 /* Disable use of CSS in the future except long idle */ 731 cubicd->flags &= ~CUBICFLAG_HYSTART_ENABLED; 732 } 733 cubic_log_hystart_event(ccv, cubicd, 6, CCV(ccv, snd_ssthresh)); 734 } 735 if (cubicd->flags & CUBICFLAG_HYSTART_ENABLED) 736 cubic_log_hystart_event(ccv, cubicd, 4, round_cnt); 737 } 738 739 DECLARE_CC_MODULE(cubic, &cubic_cc_algo); 740 MODULE_VERSION(cubic, 2); 741