tcp_congctl.c revision 1.13
1 /* $NetBSD: tcp_congctl.c,v 1.13 2007/07/11 21:34:16 xtraeme Exp $ */ 2 3 /*- 4 * Copyright (c) 1997, 1998, 1999, 2001, 2005, 2006 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Jason R. Thorpe and Kevin M. Lahey of the Numerical Aerospace Simulation 9 * Facility, NASA Ames Research Center. 10 * This code is derived from software contributed to The NetBSD Foundation 11 * by Charles M. Hannum. 12 * This code is derived from software contributed to The NetBSD Foundation 13 * by Rui Paulo. 14 * 15 * Redistribution and use in source and binary forms, with or without 16 * modification, are permitted provided that the following conditions 17 * are met: 18 * 1. Redistributions of source code must retain the above copyright 19 * notice, this list of conditions and the following disclaimer. 20 * 2. Redistributions in binary form must reproduce the above copyright 21 * notice, this list of conditions and the following disclaimer in the 22 * documentation and/or other materials provided with the distribution. 23 * 3. All advertising materials mentioning features or use of this software 24 * must display the following acknowledgement: 25 * This product includes software developed by the NetBSD 26 * Foundation, Inc. and its contributors. 27 * 4. Neither the name of The NetBSD Foundation nor the names of its 28 * contributors may be used to endorse or promote products derived 29 * from this software without specific prior written permission. 30 * 31 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 32 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 33 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 34 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 35 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 36 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 37 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 38 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 39 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 40 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 41 * POSSIBILITY OF SUCH DAMAGE. 42 */ 43 44 /* 45 * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project. 46 * All rights reserved. 47 * 48 * Redistribution and use in source and binary forms, with or without 49 * modification, are permitted provided that the following conditions 50 * are met: 51 * 1. Redistributions of source code must retain the above copyright 52 * notice, this list of conditions and the following disclaimer. 53 * 2. Redistributions in binary form must reproduce the above copyright 54 * notice, this list of conditions and the following disclaimer in the 55 * documentation and/or other materials provided with the distribution. 56 * 3. Neither the name of the project nor the names of its contributors 57 * may be used to endorse or promote products derived from this software 58 * without specific prior written permission. 59 * 60 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND 61 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 62 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 63 * ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE 64 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 65 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 66 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 67 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 68 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 69 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 70 * SUCH DAMAGE. 71 */ 72 73 /* 74 * @(#)COPYRIGHT 1.1 (NRL) 17 January 1995 75 * 76 * NRL grants permission for redistribution and use in source and binary 77 * forms, with or without modification, of the software and documentation 78 * created at NRL provided that the following conditions are met: 79 * 80 * 1. Redistributions of source code must retain the above copyright 81 * notice, this list of conditions and the following disclaimer. 82 * 2. Redistributions in binary form must reproduce the above copyright 83 * notice, this list of conditions and the following disclaimer in the 84 * documentation and/or other materials provided with the distribution. 85 * 3. All advertising materials mentioning features or use of this software 86 * must display the following acknowledgements: 87 * This product includes software developed by the University of 88 * California, Berkeley and its contributors. 89 * This product includes software developed at the Information 90 * Technology Division, US Naval Research Laboratory. 91 * 4. Neither the name of the NRL nor the names of its contributors 92 * may be used to endorse or promote products derived from this software 93 * without specific prior written permission. 94 * 95 * THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL AND CONTRIBUTORS ``AS 96 * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 97 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A 98 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL NRL OR 99 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 100 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 101 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 102 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 103 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 104 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 105 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 106 * 107 * The views and conclusions contained in the software and documentation 108 * are those of the authors and should not be interpreted as representing 109 * official policies, either expressed or implied, of the US Naval 110 * Research Laboratory (NRL). 111 */ 112 113 /* 114 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995 115 * The Regents of the University of California. All rights reserved. 116 * 117 * Redistribution and use in source and binary forms, with or without 118 * modification, are permitted provided that the following conditions 119 * are met: 120 * 1. Redistributions of source code must retain the above copyright 121 * notice, this list of conditions and the following disclaimer. 122 * 2. Redistributions in binary form must reproduce the above copyright 123 * notice, this list of conditions and the following disclaimer in the 124 * documentation and/or other materials provided with the distribution. 125 * 3. Neither the name of the University nor the names of its contributors 126 * may be used to endorse or promote products derived from this software 127 * without specific prior written permission. 128 * 129 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 130 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 131 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 132 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 133 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 134 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 135 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 136 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 137 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 138 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 139 * SUCH DAMAGE. 140 * 141 * @(#)tcp_input.c 8.12 (Berkeley) 5/24/95 142 */ 143 144 #include <sys/cdefs.h> 145 __KERNEL_RCSID(0, "$NetBSD: tcp_congctl.c,v 1.13 2007/07/11 21:34:16 xtraeme Exp $"); 146 147 #include "opt_inet.h" 148 #include "opt_tcp_debug.h" 149 #include "opt_tcp_congctl.h" 150 151 #include <sys/param.h> 152 #include <sys/systm.h> 153 #include <sys/malloc.h> 154 #include <sys/mbuf.h> 155 #include <sys/protosw.h> 156 #include <sys/socket.h> 157 #include <sys/socketvar.h> 158 #include <sys/errno.h> 159 #include <sys/syslog.h> 160 #include <sys/pool.h> 161 #include <sys/domain.h> 162 #include <sys/kernel.h> 163 #include <sys/mutex.h> 164 165 #include <net/if.h> 166 #include <net/route.h> 167 168 #include <netinet/in.h> 169 #include <netinet/in_systm.h> 170 #include <netinet/ip.h> 171 #include <netinet/in_pcb.h> 172 #include <netinet/in_var.h> 173 #include <netinet/ip_var.h> 174 175 #ifdef INET6 176 #ifndef INET 177 #include <netinet/in.h> 178 #endif 179 #include <netinet/ip6.h> 180 #include <netinet6/ip6_var.h> 181 #include <netinet6/in6_pcb.h> 182 #include <netinet6/ip6_var.h> 183 #include <netinet6/in6_var.h> 184 #include <netinet/icmp6.h> 185 #include <netinet6/nd6.h> 186 #endif 187 188 #include <netinet/tcp.h> 189 #include <netinet/tcp_fsm.h> 190 #include <netinet/tcp_seq.h> 191 #include <netinet/tcp_timer.h> 192 #include <netinet/tcp_var.h> 193 #include <netinet/tcpip.h> 194 #include <netinet/tcp_congctl.h> 195 #ifdef TCP_DEBUG 196 #include <netinet/tcp_debug.h> 197 #endif 198 199 /* 200 * TODO: 201 * consider separating the actual implementations in another file. 202 */ 203 204 static int tcp_reno_fast_retransmit(struct tcpcb *, const struct tcphdr *); 205 static void tcp_reno_slow_retransmit(struct tcpcb *); 206 static void tcp_reno_fast_retransmit_newack(struct tcpcb *, 207 const struct tcphdr *); 208 static void tcp_reno_newack(struct tcpcb *, const struct tcphdr *); 209 static void tcp_reno_congestion_exp(struct tcpcb *tp); 210 211 static int tcp_newreno_fast_retransmit(struct tcpcb *, const struct tcphdr *); 212 static void tcp_newreno_fast_retransmit_newack(struct tcpcb *, 213 const struct tcphdr *); 214 static void tcp_newreno_newack(struct tcpcb *, const struct tcphdr *); 215 216 217 static void tcp_congctl_fillnames(void); 218 219 extern int tcprexmtthresh; 220 221 MALLOC_DEFINE(M_TCPCONGCTL, "tcpcongctl", "TCP congestion control structures"); 222 223 /* 224 * Used to list the available congestion control algorithms. 225 */ 226 struct tcp_congctlent { 227 TAILQ_ENTRY(tcp_congctlent) congctl_ent; 228 char congctl_name[TCPCC_MAXLEN]; 229 struct tcp_congctl *congctl_ctl; 230 }; 231 TAILQ_HEAD(, tcp_congctlent) tcp_congctlhd; 232 233 static kmutex_t tcp_congctl_mtx; 234 235 void 236 tcp_congctl_init(void) 237 { 238 int r; 239 240 TAILQ_INIT(&tcp_congctlhd); 241 mutex_init(&tcp_congctl_mtx, MUTEX_DEFAULT, IPL_NONE); 242 243 /* Base algorithms. */ 244 r = tcp_congctl_register("reno", &tcp_reno_ctl); 245 KASSERT(r == 0); 246 r = tcp_congctl_register("newreno", &tcp_newreno_ctl); 247 KASSERT(r == 0); 248 249 /* NewReno is the default. */ 250 #ifndef TCP_CONGCTL_DEFAULT 251 #define TCP_CONGCTL_DEFAULT "newreno" 252 #endif 253 254 r = tcp_congctl_select(NULL, TCP_CONGCTL_DEFAULT); 255 KASSERT(r == 0); 256 } 257 258 /* 259 * Register a congestion algorithm and select it if we have none. 260 */ 261 int 262 tcp_congctl_register(const char *name, struct tcp_congctl *tcc) 263 { 264 struct tcp_congctlent *ntcc, *tccp; 265 266 TAILQ_FOREACH(tccp, &tcp_congctlhd, congctl_ent) 267 if (!strcmp(name, tccp->congctl_name)) { 268 /* name already registered */ 269 return EEXIST; 270 } 271 272 ntcc = malloc(sizeof(*ntcc), M_TCPCONGCTL, M_WAITOK); 273 274 strlcpy(ntcc->congctl_name, name, sizeof(ntcc->congctl_name) - 1); 275 ntcc->congctl_ctl = tcc; 276 277 TAILQ_INSERT_TAIL(&tcp_congctlhd, ntcc, congctl_ent); 278 tcp_congctl_fillnames(); 279 280 if (TAILQ_FIRST(&tcp_congctlhd) == ntcc) 281 tcp_congctl_select(NULL, name); 282 283 return 0; 284 } 285 286 int 287 tcp_congctl_unregister(const char *name) 288 { 289 struct tcp_congctlent *tccp, *rtccp; 290 unsigned int size; 291 292 rtccp = NULL; 293 size = 0; 294 TAILQ_FOREACH(tccp, &tcp_congctlhd, congctl_ent) { 295 if (!strcmp(name, tccp->congctl_name)) 296 rtccp = tccp; 297 size++; 298 } 299 300 if (!rtccp) 301 return ENOENT; 302 303 if (size <= 1 || tcp_congctl_global == rtccp->congctl_ctl || 304 rtccp->congctl_ctl->refcnt) 305 return EBUSY; 306 307 TAILQ_REMOVE(&tcp_congctlhd, rtccp, congctl_ent); 308 free(rtccp, M_TCPCONGCTL); 309 tcp_congctl_fillnames(); 310 311 return 0; 312 } 313 314 /* 315 * Select a congestion algorithm by name. 316 */ 317 int 318 tcp_congctl_select(struct tcpcb *tp, const char *name) 319 { 320 struct tcp_congctlent *tccp; 321 322 KASSERT(name); 323 324 TAILQ_FOREACH(tccp, &tcp_congctlhd, congctl_ent) 325 if (!strcmp(name, tccp->congctl_name)) { 326 if (tp) { 327 mutex_enter(&tcp_congctl_mtx); 328 tp->t_congctl->refcnt--; 329 tp->t_congctl = tccp->congctl_ctl; 330 tp->t_congctl->refcnt++; 331 mutex_exit(&tcp_congctl_mtx); 332 } else { 333 tcp_congctl_global = tccp->congctl_ctl; 334 strlcpy(tcp_congctl_global_name, 335 tccp->congctl_name, 336 sizeof(tcp_congctl_global_name) - 1); 337 } 338 return 0; 339 } 340 341 return EINVAL; 342 } 343 344 /* 345 * Returns the name of a congestion algorithm. 346 */ 347 const char * 348 tcp_congctl_bystruct(const struct tcp_congctl *tcc) 349 { 350 struct tcp_congctlent *tccp; 351 352 KASSERT(tcc); 353 354 TAILQ_FOREACH(tccp, &tcp_congctlhd, congctl_ent) 355 if (tccp->congctl_ctl == tcc) 356 return tccp->congctl_name; 357 358 return NULL; 359 } 360 361 static void 362 tcp_congctl_fillnames(void) 363 { 364 struct tcp_congctlent *tccp; 365 const char *delim = " "; 366 367 tcp_congctl_avail[0] = '\0'; 368 TAILQ_FOREACH(tccp, &tcp_congctlhd, congctl_ent) { 369 strlcat(tcp_congctl_avail, tccp->congctl_name, 370 sizeof(tcp_congctl_avail) - 1); 371 if (TAILQ_NEXT(tccp, congctl_ent)) 372 strlcat(tcp_congctl_avail, delim, 373 sizeof(tcp_congctl_avail) - 1); 374 } 375 376 } 377 378 /* ------------------------------------------------------------------------ */ 379 380 /* 381 * TCP/Reno congestion control. 382 */ 383 static void 384 tcp_reno_congestion_exp(struct tcpcb *tp) 385 { 386 u_int win; 387 388 /* 389 * Halve the congestion window and reduce the 390 * slow start threshold. 391 */ 392 win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_segsz; 393 if (win < 2) 394 win = 2; 395 396 tp->snd_ssthresh = win * tp->t_segsz; 397 tp->snd_recover = tp->snd_max; 398 tp->snd_cwnd = tp->snd_ssthresh; 399 400 /* 401 * When using TCP ECN, notify the peer that 402 * we reduced the cwnd. 403 */ 404 if (TCP_ECN_ALLOWED(tp)) 405 tp->t_flags |= TF_ECN_SND_CWR; 406 } 407 408 409 410 static int 411 tcp_reno_fast_retransmit(struct tcpcb *tp, const struct tcphdr *th) 412 { 413 /* 414 * We know we're losing at the current 415 * window size so do congestion avoidance 416 * (set ssthresh to half the current window 417 * and pull our congestion window back to 418 * the new ssthresh). 419 * 420 * Dup acks mean that packets have left the 421 * network (they're now cached at the receiver) 422 * so bump cwnd by the amount in the receiver 423 * to keep a constant cwnd packets in the 424 * network. 425 * 426 * If we are using TCP/SACK, then enter 427 * Fast Recovery if the receiver SACKs 428 * data that is tcprexmtthresh * MSS 429 * bytes past the last ACKed segment, 430 * irrespective of the number of DupAcks. 431 */ 432 433 tcp_seq onxt; 434 435 onxt = tp->snd_nxt; 436 tcp_reno_congestion_exp(tp); 437 tp->t_partialacks = 0; 438 TCP_TIMER_DISARM(tp, TCPT_REXMT); 439 tp->t_rtttime = 0; 440 if (TCP_SACK_ENABLED(tp)) { 441 tp->t_dupacks = tcprexmtthresh; 442 tp->sack_newdata = tp->snd_nxt; 443 tp->snd_cwnd = tp->t_segsz; 444 (void) tcp_output(tp); 445 return 0; 446 } 447 tp->snd_nxt = th->th_ack; 448 tp->snd_cwnd = tp->t_segsz; 449 (void) tcp_output(tp); 450 tp->snd_cwnd = tp->snd_ssthresh + tp->t_segsz * tp->t_dupacks; 451 if (SEQ_GT(onxt, tp->snd_nxt)) 452 tp->snd_nxt = onxt; 453 454 return 0; 455 } 456 457 static void 458 tcp_reno_slow_retransmit(struct tcpcb *tp) 459 { 460 u_int win; 461 462 /* 463 * Close the congestion window down to one segment 464 * (we'll open it by one segment for each ack we get). 465 * Since we probably have a window's worth of unacked 466 * data accumulated, this "slow start" keeps us from 467 * dumping all that data as back-to-back packets (which 468 * might overwhelm an intermediate gateway). 469 * 470 * There are two phases to the opening: Initially we 471 * open by one mss on each ack. This makes the window 472 * size increase exponentially with time. If the 473 * window is larger than the path can handle, this 474 * exponential growth results in dropped packet(s) 475 * almost immediately. To get more time between 476 * drops but still "push" the network to take advantage 477 * of improving conditions, we switch from exponential 478 * to linear window opening at some threshhold size. 479 * For a threshhold, we use half the current window 480 * size, truncated to a multiple of the mss. 481 * 482 * (the minimum cwnd that will give us exponential 483 * growth is 2 mss. We don't allow the threshhold 484 * to go below this.) 485 */ 486 487 win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_segsz; 488 if (win < 2) 489 win = 2; 490 /* Loss Window MUST be one segment. */ 491 tp->snd_cwnd = tp->t_segsz; 492 tp->snd_ssthresh = win * tp->t_segsz; 493 tp->t_partialacks = -1; 494 tp->t_dupacks = 0; 495 tp->t_bytes_acked = 0; 496 } 497 498 static void 499 tcp_reno_fast_retransmit_newack(struct tcpcb *tp, 500 const struct tcphdr *th) 501 { 502 if (tp->t_partialacks < 0) { 503 /* 504 * We were not in fast recovery. Reset the duplicate ack 505 * counter. 506 */ 507 tp->t_dupacks = 0; 508 } else { 509 /* 510 * Clamp the congestion window to the crossover point and 511 * exit fast recovery. 512 */ 513 if (tp->snd_cwnd > tp->snd_ssthresh) 514 tp->snd_cwnd = tp->snd_ssthresh; 515 tp->t_partialacks = -1; 516 tp->t_dupacks = 0; 517 tp->t_bytes_acked = 0; 518 } 519 } 520 521 static void 522 tcp_reno_newack(struct tcpcb *tp, const struct tcphdr *th) 523 { 524 /* 525 * When new data is acked, open the congestion window. 526 */ 527 528 u_int cw = tp->snd_cwnd; 529 u_int incr = tp->t_segsz; 530 531 if (tcp_do_abc) { 532 533 /* 534 * RFC 3465 Appropriate Byte Counting (ABC) 535 */ 536 537 int acked = th->th_ack - tp->snd_una; 538 539 if (cw >= tp->snd_ssthresh) { 540 tp->t_bytes_acked += acked; 541 if (tp->t_bytes_acked >= cw) { 542 /* Time to increase the window. */ 543 tp->t_bytes_acked -= cw; 544 } else { 545 /* No need to increase yet. */ 546 incr = 0; 547 } 548 } else { 549 /* 550 * use 2*SMSS or 1*SMSS for the "L" param, 551 * depending on sysctl setting. 552 * 553 * (See RFC 3465 2.3 Choosing the Limit) 554 */ 555 u_int abc_lim; 556 557 abc_lim = (tcp_abc_aggressive == 0 || 558 tp->snd_nxt != tp->snd_max) ? incr : incr * 2; 559 incr = min(acked, abc_lim); 560 } 561 } else { 562 563 /* 564 * If the window gives us less than ssthresh packets 565 * in flight, open exponentially (segsz per packet). 566 * Otherwise open linearly: segsz per window 567 * (segsz^2 / cwnd per packet). 568 */ 569 570 if (cw >= tp->snd_ssthresh) { 571 incr = incr * incr / cw; 572 } 573 } 574 575 tp->snd_cwnd = min(cw + incr, TCP_MAXWIN << tp->snd_scale); 576 } 577 578 struct tcp_congctl tcp_reno_ctl = { 579 .fast_retransmit = tcp_reno_fast_retransmit, 580 .slow_retransmit = tcp_reno_slow_retransmit, 581 .fast_retransmit_newack = tcp_reno_fast_retransmit_newack, 582 .newack = tcp_reno_newack, 583 .cong_exp = tcp_reno_congestion_exp, 584 }; 585 586 /* 587 * TCP/NewReno Congestion control. 588 */ 589 static int 590 tcp_newreno_fast_retransmit(struct tcpcb *tp, const struct tcphdr *th) 591 { 592 if (SEQ_LT(th->th_ack, tp->snd_high)) { 593 /* 594 * False fast retransmit after timeout. 595 * Do not enter fast recovery 596 */ 597 tp->t_dupacks = 0; 598 return 1; 599 } else { 600 /* 601 * Fast retransmit is same as reno. 602 */ 603 return tcp_reno_fast_retransmit(tp, th); 604 } 605 606 return 0; 607 } 608 609 /* 610 * Implement the NewReno response to a new ack, checking for partial acks in 611 * fast recovery. 612 */ 613 static void 614 tcp_newreno_fast_retransmit_newack(struct tcpcb *tp, const struct tcphdr *th) 615 { 616 if (tp->t_partialacks < 0) { 617 /* 618 * We were not in fast recovery. Reset the duplicate ack 619 * counter. 620 */ 621 tp->t_dupacks = 0; 622 } else if (SEQ_LT(th->th_ack, tp->snd_recover)) { 623 /* 624 * This is a partial ack. Retransmit the first unacknowledged 625 * segment and deflate the congestion window by the amount of 626 * acknowledged data. Do not exit fast recovery. 627 */ 628 tcp_seq onxt = tp->snd_nxt; 629 u_long ocwnd = tp->snd_cwnd; 630 631 /* 632 * snd_una has not yet been updated and the socket's send 633 * buffer has not yet drained off the ACK'd data, so we 634 * have to leave snd_una as it was to get the correct data 635 * offset in tcp_output(). 636 */ 637 if (++tp->t_partialacks == 1) 638 TCP_TIMER_DISARM(tp, TCPT_REXMT); 639 tp->t_rtttime = 0; 640 tp->snd_nxt = th->th_ack; 641 /* 642 * Set snd_cwnd to one segment beyond ACK'd offset. snd_una 643 * is not yet updated when we're called. 644 */ 645 tp->snd_cwnd = tp->t_segsz + (th->th_ack - tp->snd_una); 646 (void) tcp_output(tp); 647 tp->snd_cwnd = ocwnd; 648 if (SEQ_GT(onxt, tp->snd_nxt)) 649 tp->snd_nxt = onxt; 650 /* 651 * Partial window deflation. Relies on fact that tp->snd_una 652 * not updated yet. 653 */ 654 tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_segsz); 655 } else { 656 /* 657 * Complete ack. Inflate the congestion window to ssthresh 658 * and exit fast recovery. 659 * 660 * Window inflation should have left us with approx. 661 * snd_ssthresh outstanding data. But in case we 662 * would be inclined to send a burst, better to do 663 * it via the slow start mechanism. 664 */ 665 if (SEQ_SUB(tp->snd_max, th->th_ack) < tp->snd_ssthresh) 666 tp->snd_cwnd = SEQ_SUB(tp->snd_max, th->th_ack) 667 + tp->t_segsz; 668 else 669 tp->snd_cwnd = tp->snd_ssthresh; 670 tp->t_partialacks = -1; 671 tp->t_dupacks = 0; 672 tp->t_bytes_acked = 0; 673 } 674 } 675 676 static void 677 tcp_newreno_newack(struct tcpcb *tp, const struct tcphdr *th) 678 { 679 /* 680 * If we are still in fast recovery (meaning we are using 681 * NewReno and we have only received partial acks), do not 682 * inflate the window yet. 683 */ 684 if (tp->t_partialacks < 0) 685 tcp_reno_newack(tp, th); 686 } 687 688 689 struct tcp_congctl tcp_newreno_ctl = { 690 .fast_retransmit = tcp_newreno_fast_retransmit, 691 .slow_retransmit = tcp_reno_slow_retransmit, 692 .fast_retransmit_newack = tcp_newreno_fast_retransmit_newack, 693 .newack = tcp_newreno_newack, 694 .cong_exp = tcp_reno_congestion_exp, 695 }; 696 697 698
Indexes created Thu Sep 25 08:09:54 GMT 2025