2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
3 * The Regents of the University of California. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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.
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
29 * @(#)tcp_timer.c 8.2 (Berkeley) 5/24/95
32 #include <sys/cdefs.h>
33 __FBSDID("$FreeBSD$");
36 #include "opt_inet6.h"
37 #include "opt_tcpdebug.h"
39 #include <sys/param.h>
40 #include <sys/kernel.h>
43 #include <sys/mutex.h>
44 #include <sys/protosw.h>
46 #include <sys/socket.h>
47 #include <sys/socketvar.h>
48 #include <sys/sysctl.h>
49 #include <sys/systm.h>
52 #include <net/route.h>
55 #include <netinet/cc.h>
56 #include <netinet/in.h>
57 #include <netinet/in_pcb.h>
58 #include <netinet/in_systm.h>
60 #include <netinet6/in6_pcb.h>
62 #include <netinet/ip_var.h>
63 #include <netinet/tcp_fsm.h>
64 #include <netinet/tcp_timer.h>
65 #include <netinet/tcp_var.h>
66 #include <netinet/tcpip.h>
68 #include <netinet/tcp_debug.h>
72 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT|CTLFLAG_RW,
73 &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", "time to establish connection");
76 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT|CTLFLAG_RW,
77 &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", "time before keepalive probes begin");
80 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT|CTLFLAG_RW,
81 &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", "time between keepalive probes");
84 SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime, CTLTYPE_INT|CTLFLAG_RW,
85 &tcp_delacktime, 0, sysctl_msec_to_ticks, "I",
86 "Time before a delayed ACK is sent");
89 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW,
90 &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime");
93 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min, CTLTYPE_INT|CTLFLAG_RW,
94 &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I",
95 "Minimum Retransmission Timeout");
98 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop, CTLTYPE_INT|CTLFLAG_RW,
99 &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I",
100 "Retransmission Timer Slop");
102 static int always_keepalive = 1;
103 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW,
104 &always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections");
106 int tcp_fast_finwait2_recycle = 0;
107 SYSCTL_INT(_net_inet_tcp, OID_AUTO, fast_finwait2_recycle, CTLFLAG_RW,
108 &tcp_fast_finwait2_recycle, 0,
109 "Recycle closed FIN_WAIT_2 connections faster");
111 int tcp_finwait2_timeout;
112 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, finwait2_timeout, CTLTYPE_INT|CTLFLAG_RW,
113 &tcp_finwait2_timeout, 0, sysctl_msec_to_ticks, "I", "FIN-WAIT2 timeout");
115 int tcp_keepcnt = TCPTV_KEEPCNT;
116 SYSCTL_INT(_net_inet_tcp, OID_AUTO, keepcnt, CTLFLAG_RW, &tcp_keepcnt, 0,
117 "Number of keepalive probes to send");
119 /* max idle probes */
120 int tcp_maxpersistidle;
122 static int tcp_rexmit_drop_options = 1;
123 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rexmit_drop_options, CTLFLAG_RW,
124 &tcp_rexmit_drop_options, 0,
125 "Drop TCP options from 3rd and later retransmitted SYN");
127 static int per_cpu_timers = 0;
128 SYSCTL_INT(_net_inet_tcp, OID_AUTO, per_cpu_timers, CTLFLAG_RW,
129 &per_cpu_timers , 0, "run tcp timers on all cpus");
131 #define INP_CPU(inp) (per_cpu_timers ? (!CPU_ABSENT(((inp)->inp_flowid % (mp_maxid+1))) ? \
132 ((inp)->inp_flowid % (mp_maxid+1)) : curcpu) : 0)
135 * Tcp protocol timeout routine called every 500 ms.
136 * Updates timestamps used for TCP
137 * causes finite state machine actions if timers expire.
142 VNET_ITERATOR_DECL(vnet_iter);
144 VNET_LIST_RLOCK_NOSLEEP();
145 VNET_FOREACH(vnet_iter) {
146 CURVNET_SET(vnet_iter);
147 INP_INFO_WLOCK(&V_tcbinfo);
148 (void) tcp_tw_2msl_scan(0);
149 INP_INFO_WUNLOCK(&V_tcbinfo);
152 VNET_LIST_RUNLOCK_NOSLEEP();
155 int tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] =
156 { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 };
158 int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
159 { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 };
161 static int tcp_totbackoff = 2559; /* sum of tcp_backoff[] */
163 static int tcp_timer_race;
164 SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_race, CTLFLAG_RD, &tcp_timer_race,
165 0, "Count of t_inpcb races on tcp_discardcb");
168 * TCP timer processing.
172 tcp_timer_delack(void *xtp)
174 struct tcpcb *tp = xtp;
176 CURVNET_SET(tp->t_vnet);
180 * XXXRW: While this assert is in fact correct, bugs in the tcpcb
181 * tear-down mean we need it as a work-around for races between
182 * timers and tcp_discardcb().
184 * KASSERT(inp != NULL, ("tcp_timer_delack: inp == NULL"));
192 if (callout_pending(&tp->t_timers->tt_delack) ||
193 !callout_active(&tp->t_timers->tt_delack)) {
198 callout_deactivate(&tp->t_timers->tt_delack);
199 if ((inp->inp_flags & INP_DROPPED) != 0) {
205 tp->t_flags |= TF_ACKNOW;
206 TCPSTAT_INC(tcps_delack);
207 (void) tcp_output(tp);
213 tcp_timer_2msl(void *xtp)
215 struct tcpcb *tp = xtp;
217 CURVNET_SET(tp->t_vnet);
221 ostate = tp->t_state;
224 * XXXRW: Does this actually happen?
226 INP_INFO_WLOCK(&V_tcbinfo);
229 * XXXRW: While this assert is in fact correct, bugs in the tcpcb
230 * tear-down mean we need it as a work-around for races between
231 * timers and tcp_discardcb().
233 * KASSERT(inp != NULL, ("tcp_timer_2msl: inp == NULL"));
237 INP_INFO_WUNLOCK(&V_tcbinfo);
242 tcp_free_sackholes(tp);
243 if (callout_pending(&tp->t_timers->tt_2msl) ||
244 !callout_active(&tp->t_timers->tt_2msl)) {
245 INP_WUNLOCK(tp->t_inpcb);
246 INP_INFO_WUNLOCK(&V_tcbinfo);
250 callout_deactivate(&tp->t_timers->tt_2msl);
251 if ((inp->inp_flags & INP_DROPPED) != 0) {
253 INP_INFO_WUNLOCK(&V_tcbinfo);
258 * 2 MSL timeout in shutdown went off. If we're closed but
259 * still waiting for peer to close and connection has been idle
260 * too long, or if 2MSL time is up from TIME_WAIT, delete connection
261 * control block. Otherwise, check again in a bit.
263 * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed,
264 * there's no point in hanging onto FIN_WAIT_2 socket. Just close it.
265 * Ignore fact that there were recent incoming segments.
267 if (tcp_fast_finwait2_recycle && tp->t_state == TCPS_FIN_WAIT_2 &&
268 tp->t_inpcb && tp->t_inpcb->inp_socket &&
269 (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE)) {
270 TCPSTAT_INC(tcps_finwait2_drops);
273 if (tp->t_state != TCPS_TIME_WAIT &&
274 ticks - tp->t_rcvtime <= TP_MAXIDLE(tp))
275 callout_reset_on(&tp->t_timers->tt_2msl,
276 TP_KEEPINTVL(tp), tcp_timer_2msl, tp, INP_CPU(inp));
282 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
283 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
288 INP_INFO_WUNLOCK(&V_tcbinfo);
293 tcp_timer_keep(void *xtp)
295 struct tcpcb *tp = xtp;
296 struct tcptemp *t_template;
298 CURVNET_SET(tp->t_vnet);
302 ostate = tp->t_state;
304 INP_INFO_WLOCK(&V_tcbinfo);
307 * XXXRW: While this assert is in fact correct, bugs in the tcpcb
308 * tear-down mean we need it as a work-around for races between
309 * timers and tcp_discardcb().
311 * KASSERT(inp != NULL, ("tcp_timer_keep: inp == NULL"));
315 INP_INFO_WUNLOCK(&V_tcbinfo);
320 if (callout_pending(&tp->t_timers->tt_keep) ||
321 !callout_active(&tp->t_timers->tt_keep)) {
323 INP_INFO_WUNLOCK(&V_tcbinfo);
327 callout_deactivate(&tp->t_timers->tt_keep);
328 if ((inp->inp_flags & INP_DROPPED) != 0) {
330 INP_INFO_WUNLOCK(&V_tcbinfo);
335 * Keep-alive timer went off; send something
336 * or drop connection if idle for too long.
338 TCPSTAT_INC(tcps_keeptimeo);
339 if (tp->t_state < TCPS_ESTABLISHED)
341 if ((always_keepalive || inp->inp_socket->so_options & SO_KEEPALIVE) &&
342 tp->t_state <= TCPS_CLOSING) {
343 if (ticks - tp->t_rcvtime >= TP_KEEPIDLE(tp) + TP_MAXIDLE(tp))
346 * Send a packet designed to force a response
347 * if the peer is up and reachable:
348 * either an ACK if the connection is still alive,
349 * or an RST if the peer has closed the connection
350 * due to timeout or reboot.
351 * Using sequence number tp->snd_una-1
352 * causes the transmitted zero-length segment
353 * to lie outside the receive window;
354 * by the protocol spec, this requires the
355 * correspondent TCP to respond.
357 TCPSTAT_INC(tcps_keepprobe);
358 t_template = tcpip_maketemplate(inp);
360 tcp_respond(tp, t_template->tt_ipgen,
361 &t_template->tt_t, (struct mbuf *)NULL,
362 tp->rcv_nxt, tp->snd_una - 1, 0);
363 free(t_template, M_TEMP);
365 callout_reset_on(&tp->t_timers->tt_keep, TP_KEEPINTVL(tp),
366 tcp_timer_keep, tp, INP_CPU(inp));
368 callout_reset_on(&tp->t_timers->tt_keep, TP_KEEPIDLE(tp),
369 tcp_timer_keep, tp, INP_CPU(inp));
372 if (inp->inp_socket->so_options & SO_DEBUG)
373 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
377 INP_INFO_WUNLOCK(&V_tcbinfo);
382 TCPSTAT_INC(tcps_keepdrops);
383 tp = tcp_drop(tp, ETIMEDOUT);
386 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
387 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
391 INP_WUNLOCK(tp->t_inpcb);
392 INP_INFO_WUNLOCK(&V_tcbinfo);
397 tcp_timer_persist(void *xtp)
399 struct tcpcb *tp = xtp;
401 CURVNET_SET(tp->t_vnet);
405 ostate = tp->t_state;
407 INP_INFO_WLOCK(&V_tcbinfo);
410 * XXXRW: While this assert is in fact correct, bugs in the tcpcb
411 * tear-down mean we need it as a work-around for races between
412 * timers and tcp_discardcb().
414 * KASSERT(inp != NULL, ("tcp_timer_persist: inp == NULL"));
418 INP_INFO_WUNLOCK(&V_tcbinfo);
423 if (callout_pending(&tp->t_timers->tt_persist) ||
424 !callout_active(&tp->t_timers->tt_persist)) {
426 INP_INFO_WUNLOCK(&V_tcbinfo);
430 callout_deactivate(&tp->t_timers->tt_persist);
431 if ((inp->inp_flags & INP_DROPPED) != 0) {
433 INP_INFO_WUNLOCK(&V_tcbinfo);
438 * Persistance timer into zero window.
439 * Force a byte to be output, if possible.
441 TCPSTAT_INC(tcps_persisttimeo);
443 * Hack: if the peer is dead/unreachable, we do not
444 * time out if the window is closed. After a full
445 * backoff, drop the connection if the idle time
446 * (no responses to probes) reaches the maximum
447 * backoff that we would use if retransmitting.
449 if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
450 (ticks - tp->t_rcvtime >= tcp_maxpersistidle ||
451 ticks - tp->t_rcvtime >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
452 TCPSTAT_INC(tcps_persistdrop);
453 tp = tcp_drop(tp, ETIMEDOUT);
457 tp->t_flags |= TF_FORCEDATA;
458 (void) tcp_output(tp);
459 tp->t_flags &= ~TF_FORCEDATA;
463 if (tp != NULL && tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
464 tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
468 INP_INFO_WUNLOCK(&V_tcbinfo);
473 tcp_timer_rexmt(void * xtp)
475 struct tcpcb *tp = xtp;
476 CURVNET_SET(tp->t_vnet);
483 ostate = tp->t_state;
485 INP_INFO_RLOCK(&V_tcbinfo);
488 * XXXRW: While this assert is in fact correct, bugs in the tcpcb
489 * tear-down mean we need it as a work-around for races between
490 * timers and tcp_discardcb().
492 * KASSERT(inp != NULL, ("tcp_timer_rexmt: inp == NULL"));
496 INP_INFO_RUNLOCK(&V_tcbinfo);
501 if (callout_pending(&tp->t_timers->tt_rexmt) ||
502 !callout_active(&tp->t_timers->tt_rexmt)) {
504 INP_INFO_RUNLOCK(&V_tcbinfo);
508 callout_deactivate(&tp->t_timers->tt_rexmt);
509 if ((inp->inp_flags & INP_DROPPED) != 0) {
511 INP_INFO_RUNLOCK(&V_tcbinfo);
515 tcp_free_sackholes(tp);
517 * Retransmission timer went off. Message has not
518 * been acked within retransmit interval. Back off
519 * to a longer retransmit interval and retransmit one segment.
521 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
522 tp->t_rxtshift = TCP_MAXRXTSHIFT;
523 TCPSTAT_INC(tcps_timeoutdrop);
525 INP_INFO_RUNLOCK(&V_tcbinfo);
527 INP_INFO_WLOCK(&V_tcbinfo);
529 if (in_pcbrele_wlocked(inp)) {
530 INP_INFO_WUNLOCK(&V_tcbinfo);
534 if (inp->inp_flags & INP_DROPPED) {
536 INP_INFO_WUNLOCK(&V_tcbinfo);
541 tp = tcp_drop(tp, tp->t_softerror ?
542 tp->t_softerror : ETIMEDOUT);
546 INP_INFO_RUNLOCK(&V_tcbinfo);
548 if (tp->t_state == TCPS_SYN_SENT) {
550 * If the SYN was retransmitted, indicate CWND to be
551 * limited to 1 segment in cc_conn_init().
554 } else if (tp->t_rxtshift == 1) {
556 * first retransmit; record ssthresh and cwnd so they can
557 * be recovered if this turns out to be a "bad" retransmit.
558 * A retransmit is considered "bad" if an ACK for this
559 * segment is received within RTT/2 interval; the assumption
560 * here is that the ACK was already in flight. See
561 * "On Estimating End-to-End Network Path Properties" by
562 * Allman and Paxson for more details.
564 tp->snd_cwnd_prev = tp->snd_cwnd;
565 tp->snd_ssthresh_prev = tp->snd_ssthresh;
566 tp->snd_recover_prev = tp->snd_recover;
567 if (IN_FASTRECOVERY(tp->t_flags))
568 tp->t_flags |= TF_WASFRECOVERY;
570 tp->t_flags &= ~TF_WASFRECOVERY;
571 if (IN_CONGRECOVERY(tp->t_flags))
572 tp->t_flags |= TF_WASCRECOVERY;
574 tp->t_flags &= ~TF_WASCRECOVERY;
575 tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
576 tp->t_flags |= TF_PREVVALID;
578 tp->t_flags &= ~TF_PREVVALID;
579 TCPSTAT_INC(tcps_rexmttimeo);
580 if (tp->t_state == TCPS_SYN_SENT)
581 rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift];
583 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
584 TCPT_RANGESET(tp->t_rxtcur, rexmt,
585 tp->t_rttmin, TCPTV_REXMTMAX);
587 * Disable rfc1323 if we haven't got any response to
588 * our third SYN to work-around some broken terminal servers
589 * (most of which have hopefully been retired) that have bad VJ
590 * header compression code which trashes TCP segments containing
591 * unknown-to-them TCP options.
593 if (tcp_rexmit_drop_options && (tp->t_state == TCPS_SYN_SENT) &&
594 (tp->t_rxtshift == 3))
595 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP);
597 * If we backed off this far, our srtt estimate is probably bogus.
598 * Clobber it so we'll take the next rtt measurement as our srtt;
599 * move the current srtt into rttvar to keep the current
600 * retransmit times until then.
602 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
604 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
605 in6_losing(tp->t_inpcb);
608 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
611 tp->snd_nxt = tp->snd_una;
612 tp->snd_recover = tp->snd_max;
614 * Force a segment to be sent.
616 tp->t_flags |= TF_ACKNOW;
618 * If timing a segment in this window, stop the timer.
622 cc_cong_signal(tp, NULL, CC_RTO);
624 (void) tcp_output(tp);
628 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
629 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
635 INP_INFO_WUNLOCK(&V_tcbinfo);
640 tcp_timer_activate(struct tcpcb *tp, int timer_type, u_int delta)
642 struct callout *t_callout;
644 struct inpcb *inp = tp->t_inpcb;
645 int cpu = INP_CPU(inp);
648 if (tp->t_flags & TF_TOE)
652 switch (timer_type) {
654 t_callout = &tp->t_timers->tt_delack;
655 f_callout = tcp_timer_delack;
658 t_callout = &tp->t_timers->tt_rexmt;
659 f_callout = tcp_timer_rexmt;
662 t_callout = &tp->t_timers->tt_persist;
663 f_callout = tcp_timer_persist;
666 t_callout = &tp->t_timers->tt_keep;
667 f_callout = tcp_timer_keep;
670 t_callout = &tp->t_timers->tt_2msl;
671 f_callout = tcp_timer_2msl;
674 panic("bad timer_type");
677 callout_stop(t_callout);
679 callout_reset_on(t_callout, delta, f_callout, tp, cpu);
684 tcp_timer_active(struct tcpcb *tp, int timer_type)
686 struct callout *t_callout;
688 switch (timer_type) {
690 t_callout = &tp->t_timers->tt_delack;
693 t_callout = &tp->t_timers->tt_rexmt;
696 t_callout = &tp->t_timers->tt_persist;
699 t_callout = &tp->t_timers->tt_keep;
702 t_callout = &tp->t_timers->tt_2msl;
705 panic("bad timer_type");
707 return callout_active(t_callout);
710 #define ticks_to_msecs(t) (1000*(t) / hz)
713 tcp_timer_to_xtimer(struct tcpcb *tp, struct tcp_timer *timer, struct xtcp_timer *xtimer)
715 bzero(xtimer, sizeof(struct xtcp_timer));
718 if (callout_active(&timer->tt_delack))
719 xtimer->tt_delack = ticks_to_msecs(timer->tt_delack.c_time - ticks);
720 if (callout_active(&timer->tt_rexmt))
721 xtimer->tt_rexmt = ticks_to_msecs(timer->tt_rexmt.c_time - ticks);
722 if (callout_active(&timer->tt_persist))
723 xtimer->tt_persist = ticks_to_msecs(timer->tt_persist.c_time - ticks);
724 if (callout_active(&timer->tt_keep))
725 xtimer->tt_keep = ticks_to_msecs(timer->tt_keep.c_time - ticks);
726 if (callout_active(&timer->tt_2msl))
727 xtimer->tt_2msl = ticks_to_msecs(timer->tt_2msl.c_time - ticks);
728 xtimer->t_rcvtime = ticks_to_msecs(ticks - tp->t_rcvtime);