Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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sys/netinet/tcp_timer.c
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1 /*- 2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 4. Neither the name of the University nor the names of its contributors 14 * may be used to endorse or promote products derived from this software 15 * without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * @(#)tcp_timer.c 8.2 (Berkeley) 5/24/95 30 */ 31 32 #include <sys/cdefs.h> 33 __FBSDID("$FreeBSD: releng/8.1/sys/netinet/tcp_timer.c 208768 2010-06-03 09:06:50Z rwatson $"); 34 35 #include "opt_inet6.h" 36 #include "opt_tcpdebug.h" 37 38 #include <sys/param.h> 39 #include <sys/kernel.h> 40 #include <sys/lock.h> 41 #include <sys/mbuf.h> 42 #include <sys/mutex.h> 43 #include <sys/protosw.h> 44 #include <sys/socket.h> 45 #include <sys/socketvar.h> 46 #include <sys/sysctl.h> 47 #include <sys/systm.h> 48 49 #include <net/if.h> 50 #include <net/route.h> 51 #include <net/vnet.h> 52 53 #include <netinet/in.h> 54 #include <netinet/in_pcb.h> 55 #include <netinet/in_systm.h> 56 #ifdef INET6 57 #include <netinet6/in6_pcb.h> 58 #endif 59 #include <netinet/ip_var.h> 60 #include <netinet/tcp.h> 61 #include <netinet/tcp_fsm.h> 62 #include <netinet/tcp_timer.h> 63 #include <netinet/tcp_var.h> 64 #include <netinet/tcpip.h> 65 #ifdef TCPDEBUG 66 #include <netinet/tcp_debug.h> 67 #endif 68 69 int tcp_keepinit; 70 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT|CTLFLAG_RW, 71 &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", "time to establish connection"); 72 73 int tcp_keepidle; 74 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT|CTLFLAG_RW, 75 &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", "time before keepalive probes begin"); 76 77 int tcp_keepintvl; 78 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT|CTLFLAG_RW, 79 &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", "time between keepalive probes"); 80 81 int tcp_delacktime; 82 SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime, CTLTYPE_INT|CTLFLAG_RW, 83 &tcp_delacktime, 0, sysctl_msec_to_ticks, "I", 84 "Time before a delayed ACK is sent"); 85 86 int tcp_msl; 87 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW, 88 &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime"); 89 90 int tcp_rexmit_min; 91 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min, CTLTYPE_INT|CTLFLAG_RW, 92 &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I", 93 "Minimum Retransmission Timeout"); 94 95 int tcp_rexmit_slop; 96 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop, CTLTYPE_INT|CTLFLAG_RW, 97 &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I", 98 "Retransmission Timer Slop"); 99 100 static int always_keepalive = 1; 101 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW, 102 &always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections"); 103 104 int tcp_fast_finwait2_recycle = 0; 105 SYSCTL_INT(_net_inet_tcp, OID_AUTO, fast_finwait2_recycle, CTLFLAG_RW, 106 &tcp_fast_finwait2_recycle, 0, 107 "Recycle closed FIN_WAIT_2 connections faster"); 108 109 int tcp_finwait2_timeout; 110 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, finwait2_timeout, CTLTYPE_INT|CTLFLAG_RW, 111 &tcp_finwait2_timeout, 0, sysctl_msec_to_ticks, "I", "FIN-WAIT2 timeout"); 112 113 114 static int tcp_keepcnt = TCPTV_KEEPCNT; 115 /* max idle probes */ 116 int tcp_maxpersistidle; 117 /* max idle time in persist */ 118 int tcp_maxidle; 119 120 /* 121 * Tcp protocol timeout routine called every 500 ms. 122 * Updates timestamps used for TCP 123 * causes finite state machine actions if timers expire. 124 */ 125 void 126 tcp_slowtimo(void) 127 { 128 VNET_ITERATOR_DECL(vnet_iter); 129 130 VNET_LIST_RLOCK_NOSLEEP(); 131 VNET_FOREACH(vnet_iter) { 132 CURVNET_SET(vnet_iter); 133 tcp_maxidle = tcp_keepcnt * tcp_keepintvl; 134 INP_INFO_WLOCK(&V_tcbinfo); 135 (void) tcp_tw_2msl_scan(0); 136 INP_INFO_WUNLOCK(&V_tcbinfo); 137 CURVNET_RESTORE(); 138 } 139 VNET_LIST_RUNLOCK_NOSLEEP(); 140 } 141 142 int tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] = 143 { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 }; 144 145 int tcp_backoff[TCP_MAXRXTSHIFT + 1] = 146 { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 }; 147 148 static int tcp_totbackoff = 2559; /* sum of tcp_backoff[] */ 149 150 static int tcp_timer_race; 151 SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_race, CTLFLAG_RD, &tcp_timer_race, 152 0, "Count of t_inpcb races on tcp_discardcb"); 153 154 /* 155 * TCP timer processing. 156 */ 157 158 void 159 tcp_timer_delack(void *xtp) 160 { 161 struct tcpcb *tp = xtp; 162 struct inpcb *inp; 163 CURVNET_SET(tp->t_vnet); 164 165 inp = tp->t_inpcb; 166 /* 167 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 168 * tear-down mean we need it as a work-around for races between 169 * timers and tcp_discardcb(). 170 * 171 * KASSERT(inp != NULL, ("tcp_timer_delack: inp == NULL")); 172 */ 173 if (inp == NULL) { 174 tcp_timer_race++; 175 CURVNET_RESTORE(); 176 return; 177 } 178 INP_WLOCK(inp); 179 if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_delack) 180 || !callout_active(&tp->t_timers->tt_delack)) { 181 INP_WUNLOCK(inp); 182 CURVNET_RESTORE(); 183 return; 184 } 185 callout_deactivate(&tp->t_timers->tt_delack); 186 187 tp->t_flags |= TF_ACKNOW; 188 TCPSTAT_INC(tcps_delack); 189 (void) tcp_output(tp); 190 INP_WUNLOCK(inp); 191 CURVNET_RESTORE(); 192 } 193 194 void 195 tcp_timer_2msl(void *xtp) 196 { 197 struct tcpcb *tp = xtp; 198 struct inpcb *inp; 199 CURVNET_SET(tp->t_vnet); 200 #ifdef TCPDEBUG 201 int ostate; 202 203 ostate = tp->t_state; 204 #endif 205 /* 206 * XXXRW: Does this actually happen? 207 */ 208 INP_INFO_WLOCK(&V_tcbinfo); 209 inp = tp->t_inpcb; 210 /* 211 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 212 * tear-down mean we need it as a work-around for races between 213 * timers and tcp_discardcb(). 214 * 215 * KASSERT(inp != NULL, ("tcp_timer_2msl: inp == NULL")); 216 */ 217 if (inp == NULL) { 218 tcp_timer_race++; 219 INP_INFO_WUNLOCK(&V_tcbinfo); 220 CURVNET_RESTORE(); 221 return; 222 } 223 INP_WLOCK(inp); 224 tcp_free_sackholes(tp); 225 if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_2msl) || 226 !callout_active(&tp->t_timers->tt_2msl)) { 227 INP_WUNLOCK(tp->t_inpcb); 228 INP_INFO_WUNLOCK(&V_tcbinfo); 229 CURVNET_RESTORE(); 230 return; 231 } 232 callout_deactivate(&tp->t_timers->tt_2msl); 233 /* 234 * 2 MSL timeout in shutdown went off. If we're closed but 235 * still waiting for peer to close and connection has been idle 236 * too long, or if 2MSL time is up from TIME_WAIT, delete connection 237 * control block. Otherwise, check again in a bit. 238 * 239 * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed, 240 * there's no point in hanging onto FIN_WAIT_2 socket. Just close it. 241 * Ignore fact that there were recent incoming segments. 242 */ 243 if (tcp_fast_finwait2_recycle && tp->t_state == TCPS_FIN_WAIT_2 && 244 tp->t_inpcb && tp->t_inpcb->inp_socket && 245 (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE)) { 246 TCPSTAT_INC(tcps_finwait2_drops); 247 tp = tcp_close(tp); 248 } else { 249 if (tp->t_state != TCPS_TIME_WAIT && 250 ticks - tp->t_rcvtime <= tcp_maxidle) 251 callout_reset(&tp->t_timers->tt_2msl, tcp_keepintvl, 252 tcp_timer_2msl, tp); 253 else 254 tp = tcp_close(tp); 255 } 256 257 #ifdef TCPDEBUG 258 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 259 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 260 PRU_SLOWTIMO); 261 #endif 262 if (tp != NULL) 263 INP_WUNLOCK(inp); 264 INP_INFO_WUNLOCK(&V_tcbinfo); 265 CURVNET_RESTORE(); 266 } 267 268 void 269 tcp_timer_keep(void *xtp) 270 { 271 struct tcpcb *tp = xtp; 272 struct tcptemp *t_template; 273 struct inpcb *inp; 274 CURVNET_SET(tp->t_vnet); 275 #ifdef TCPDEBUG 276 int ostate; 277 278 ostate = tp->t_state; 279 #endif 280 INP_INFO_WLOCK(&V_tcbinfo); 281 inp = tp->t_inpcb; 282 /* 283 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 284 * tear-down mean we need it as a work-around for races between 285 * timers and tcp_discardcb(). 286 * 287 * KASSERT(inp != NULL, ("tcp_timer_keep: inp == NULL")); 288 */ 289 if (inp == NULL) { 290 tcp_timer_race++; 291 INP_INFO_WUNLOCK(&V_tcbinfo); 292 CURVNET_RESTORE(); 293 return; 294 } 295 INP_WLOCK(inp); 296 if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_keep) 297 || !callout_active(&tp->t_timers->tt_keep)) { 298 INP_WUNLOCK(inp); 299 INP_INFO_WUNLOCK(&V_tcbinfo); 300 CURVNET_RESTORE(); 301 return; 302 } 303 callout_deactivate(&tp->t_timers->tt_keep); 304 /* 305 * Keep-alive timer went off; send something 306 * or drop connection if idle for too long. 307 */ 308 TCPSTAT_INC(tcps_keeptimeo); 309 if (tp->t_state < TCPS_ESTABLISHED) 310 goto dropit; 311 if ((always_keepalive || inp->inp_socket->so_options & SO_KEEPALIVE) && 312 tp->t_state <= TCPS_CLOSING) { 313 if (ticks - tp->t_rcvtime >= tcp_keepidle + tcp_maxidle) 314 goto dropit; 315 /* 316 * Send a packet designed to force a response 317 * if the peer is up and reachable: 318 * either an ACK if the connection is still alive, 319 * or an RST if the peer has closed the connection 320 * due to timeout or reboot. 321 * Using sequence number tp->snd_una-1 322 * causes the transmitted zero-length segment 323 * to lie outside the receive window; 324 * by the protocol spec, this requires the 325 * correspondent TCP to respond. 326 */ 327 TCPSTAT_INC(tcps_keepprobe); 328 t_template = tcpip_maketemplate(inp); 329 if (t_template) { 330 tcp_respond(tp, t_template->tt_ipgen, 331 &t_template->tt_t, (struct mbuf *)NULL, 332 tp->rcv_nxt, tp->snd_una - 1, 0); 333 free(t_template, M_TEMP); 334 } 335 callout_reset(&tp->t_timers->tt_keep, tcp_keepintvl, tcp_timer_keep, tp); 336 } else 337 callout_reset(&tp->t_timers->tt_keep, tcp_keepidle, tcp_timer_keep, tp); 338 339 #ifdef TCPDEBUG 340 if (inp->inp_socket->so_options & SO_DEBUG) 341 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 342 PRU_SLOWTIMO); 343 #endif 344 INP_WUNLOCK(inp); 345 INP_INFO_WUNLOCK(&V_tcbinfo); 346 CURVNET_RESTORE(); 347 return; 348 349 dropit: 350 TCPSTAT_INC(tcps_keepdrops); 351 tp = tcp_drop(tp, ETIMEDOUT); 352 353 #ifdef TCPDEBUG 354 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 355 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 356 PRU_SLOWTIMO); 357 #endif 358 if (tp != NULL) 359 INP_WUNLOCK(tp->t_inpcb); 360 INP_INFO_WUNLOCK(&V_tcbinfo); 361 CURVNET_RESTORE(); 362 } 363 364 void 365 tcp_timer_persist(void *xtp) 366 { 367 struct tcpcb *tp = xtp; 368 struct inpcb *inp; 369 CURVNET_SET(tp->t_vnet); 370 #ifdef TCPDEBUG 371 int ostate; 372 373 ostate = tp->t_state; 374 #endif 375 INP_INFO_WLOCK(&V_tcbinfo); 376 inp = tp->t_inpcb; 377 /* 378 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 379 * tear-down mean we need it as a work-around for races between 380 * timers and tcp_discardcb(). 381 * 382 * KASSERT(inp != NULL, ("tcp_timer_persist: inp == NULL")); 383 */ 384 if (inp == NULL) { 385 tcp_timer_race++; 386 INP_INFO_WUNLOCK(&V_tcbinfo); 387 CURVNET_RESTORE(); 388 return; 389 } 390 INP_WLOCK(inp); 391 if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_persist) 392 || !callout_active(&tp->t_timers->tt_persist)) { 393 INP_WUNLOCK(inp); 394 INP_INFO_WUNLOCK(&V_tcbinfo); 395 CURVNET_RESTORE(); 396 return; 397 } 398 callout_deactivate(&tp->t_timers->tt_persist); 399 /* 400 * Persistance timer into zero window. 401 * Force a byte to be output, if possible. 402 */ 403 TCPSTAT_INC(tcps_persisttimeo); 404 /* 405 * Hack: if the peer is dead/unreachable, we do not 406 * time out if the window is closed. After a full 407 * backoff, drop the connection if the idle time 408 * (no responses to probes) reaches the maximum 409 * backoff that we would use if retransmitting. 410 */ 411 if (tp->t_rxtshift == TCP_MAXRXTSHIFT && 412 (ticks - tp->t_rcvtime >= tcp_maxpersistidle || 413 ticks - tp->t_rcvtime >= TCP_REXMTVAL(tp) * tcp_totbackoff)) { 414 TCPSTAT_INC(tcps_persistdrop); 415 tp = tcp_drop(tp, ETIMEDOUT); 416 goto out; 417 } 418 tcp_setpersist(tp); 419 tp->t_flags |= TF_FORCEDATA; 420 (void) tcp_output(tp); 421 tp->t_flags &= ~TF_FORCEDATA; 422 423 out: 424 #ifdef TCPDEBUG 425 if (tp != NULL && tp->t_inpcb->inp_socket->so_options & SO_DEBUG) 426 tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO); 427 #endif 428 if (tp != NULL) 429 INP_WUNLOCK(inp); 430 INP_INFO_WUNLOCK(&V_tcbinfo); 431 CURVNET_RESTORE(); 432 } 433 434 void 435 tcp_timer_rexmt(void * xtp) 436 { 437 struct tcpcb *tp = xtp; 438 CURVNET_SET(tp->t_vnet); 439 int rexmt; 440 int headlocked; 441 struct inpcb *inp; 442 #ifdef TCPDEBUG 443 int ostate; 444 445 ostate = tp->t_state; 446 #endif 447 INP_INFO_WLOCK(&V_tcbinfo); 448 headlocked = 1; 449 inp = tp->t_inpcb; 450 /* 451 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 452 * tear-down mean we need it as a work-around for races between 453 * timers and tcp_discardcb(). 454 * 455 * KASSERT(inp != NULL, ("tcp_timer_rexmt: inp == NULL")); 456 */ 457 if (inp == NULL) { 458 tcp_timer_race++; 459 INP_INFO_WUNLOCK(&V_tcbinfo); 460 CURVNET_RESTORE(); 461 return; 462 } 463 INP_WLOCK(inp); 464 if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_rexmt) 465 || !callout_active(&tp->t_timers->tt_rexmt)) { 466 INP_WUNLOCK(inp); 467 INP_INFO_WUNLOCK(&V_tcbinfo); 468 CURVNET_RESTORE(); 469 return; 470 } 471 callout_deactivate(&tp->t_timers->tt_rexmt); 472 tcp_free_sackholes(tp); 473 /* 474 * Retransmission timer went off. Message has not 475 * been acked within retransmit interval. Back off 476 * to a longer retransmit interval and retransmit one segment. 477 */ 478 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) { 479 tp->t_rxtshift = TCP_MAXRXTSHIFT; 480 TCPSTAT_INC(tcps_timeoutdrop); 481 tp = tcp_drop(tp, tp->t_softerror ? 482 tp->t_softerror : ETIMEDOUT); 483 goto out; 484 } 485 INP_INFO_WUNLOCK(&V_tcbinfo); 486 headlocked = 0; 487 if (tp->t_rxtshift == 1) { 488 /* 489 * first retransmit; record ssthresh and cwnd so they can 490 * be recovered if this turns out to be a "bad" retransmit. 491 * A retransmit is considered "bad" if an ACK for this 492 * segment is received within RTT/2 interval; the assumption 493 * here is that the ACK was already in flight. See 494 * "On Estimating End-to-End Network Path Properties" by 495 * Allman and Paxson for more details. 496 */ 497 tp->snd_cwnd_prev = tp->snd_cwnd; 498 tp->snd_ssthresh_prev = tp->snd_ssthresh; 499 tp->snd_recover_prev = tp->snd_recover; 500 if (IN_FASTRECOVERY(tp)) 501 tp->t_flags |= TF_WASFRECOVERY; 502 else 503 tp->t_flags &= ~TF_WASFRECOVERY; 504 tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1)); 505 } 506 TCPSTAT_INC(tcps_rexmttimeo); 507 if (tp->t_state == TCPS_SYN_SENT) 508 rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift]; 509 else 510 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift]; 511 TCPT_RANGESET(tp->t_rxtcur, rexmt, 512 tp->t_rttmin, TCPTV_REXMTMAX); 513 /* 514 * Disable rfc1323 if we havn't got any response to 515 * our third SYN to work-around some broken terminal servers 516 * (most of which have hopefully been retired) that have bad VJ 517 * header compression code which trashes TCP segments containing 518 * unknown-to-them TCP options. 519 */ 520 if ((tp->t_state == TCPS_SYN_SENT) && (tp->t_rxtshift == 3)) 521 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP); 522 /* 523 * If we backed off this far, our srtt estimate is probably bogus. 524 * Clobber it so we'll take the next rtt measurement as our srtt; 525 * move the current srtt into rttvar to keep the current 526 * retransmit times until then. 527 */ 528 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) { 529 #ifdef INET6 530 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) 531 in6_losing(tp->t_inpcb); 532 else 533 #endif 534 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT); 535 tp->t_srtt = 0; 536 } 537 tp->snd_nxt = tp->snd_una; 538 tp->snd_recover = tp->snd_max; 539 /* 540 * Force a segment to be sent. 541 */ 542 tp->t_flags |= TF_ACKNOW; 543 /* 544 * If timing a segment in this window, stop the timer. 545 */ 546 tp->t_rtttime = 0; 547 /* 548 * Close the congestion window down to one segment 549 * (we'll open it by one segment for each ack we get). 550 * Since we probably have a window's worth of unacked 551 * data accumulated, this "slow start" keeps us from 552 * dumping all that data as back-to-back packets (which 553 * might overwhelm an intermediate gateway). 554 * 555 * There are two phases to the opening: Initially we 556 * open by one mss on each ack. This makes the window 557 * size increase exponentially with time. If the 558 * window is larger than the path can handle, this 559 * exponential growth results in dropped packet(s) 560 * almost immediately. To get more time between 561 * drops but still "push" the network to take advantage 562 * of improving conditions, we switch from exponential 563 * to linear window opening at some threshhold size. 564 * For a threshhold, we use half the current window 565 * size, truncated to a multiple of the mss. 566 * 567 * (the minimum cwnd that will give us exponential 568 * growth is 2 mss. We don't allow the threshhold 569 * to go below this.) 570 */ 571 { 572 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; 573 if (win < 2) 574 win = 2; 575 tp->snd_cwnd = tp->t_maxseg; 576 tp->snd_ssthresh = win * tp->t_maxseg; 577 tp->t_dupacks = 0; 578 } 579 EXIT_FASTRECOVERY(tp); 580 tp->t_bytes_acked = 0; 581 (void) tcp_output(tp); 582 583 out: 584 #ifdef TCPDEBUG 585 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 586 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 587 PRU_SLOWTIMO); 588 #endif 589 if (tp != NULL) 590 INP_WUNLOCK(inp); 591 if (headlocked) 592 INP_INFO_WUNLOCK(&V_tcbinfo); 593 CURVNET_RESTORE(); 594 } 595 596 void 597 tcp_timer_activate(struct tcpcb *tp, int timer_type, u_int delta) 598 { 599 struct callout *t_callout; 600 void *f_callout; 601 602 switch (timer_type) { 603 case TT_DELACK: 604 t_callout = &tp->t_timers->tt_delack; 605 f_callout = tcp_timer_delack; 606 break; 607 case TT_REXMT: 608 t_callout = &tp->t_timers->tt_rexmt; 609 f_callout = tcp_timer_rexmt; 610 break; 611 case TT_PERSIST: 612 t_callout = &tp->t_timers->tt_persist; 613 f_callout = tcp_timer_persist; 614 break; 615 case TT_KEEP: 616 t_callout = &tp->t_timers->tt_keep; 617 f_callout = tcp_timer_keep; 618 break; 619 case TT_2MSL: 620 t_callout = &tp->t_timers->tt_2msl; 621 f_callout = tcp_timer_2msl; 622 break; 623 default: 624 panic("bad timer_type"); 625 } 626 if (delta == 0) { 627 callout_stop(t_callout); 628 } else { 629 callout_reset(t_callout, delta, f_callout, tp); 630 } 631 } 632 633 int 634 tcp_timer_active(struct tcpcb *tp, int timer_type) 635 { 636 struct callout *t_callout; 637 638 switch (timer_type) { 639 case TT_DELACK: 640 t_callout = &tp->t_timers->tt_delack; 641 break; 642 case TT_REXMT: 643 t_callout = &tp->t_timers->tt_rexmt; 644 break; 645 case TT_PERSIST: 646 t_callout = &tp->t_timers->tt_persist; 647 break; 648 case TT_KEEP: 649 t_callout = &tp->t_timers->tt_keep; 650 break; 651 case TT_2MSL: 652 t_callout = &tp->t_timers->tt_2msl; 653 break; 654 default: 655 panic("bad timer_type"); 656 } 657 return callout_active(t_callout); 658 }
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