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33 * @(#)tcp_timer.c 8.2 (Berkeley) 5/24/95
34 * $FreeBSD: src/sys/netinet/tcp_timer.c,v 1.34.2.14 2003/02/03 02:33:41 hsu Exp $
37 #include "opt_compat.h"
38 #include "opt_inet6.h"
39 #include "opt_tcpdebug.h"
41 #include <sys/param.h>
42 #include <sys/systm.h>
43 #include <sys/kernel.h>
45 #include <sys/sysctl.h>
46 #include <sys/socket.h>
47 #include <sys/socketvar.h>
48 #include <sys/protosw.h>
50 #include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */
52 #include <net/route.h>
54 #include <netinet/in.h>
55 #include <netinet/in_systm.h>
56 #include <netinet/in_pcb.h>
58 #include <netinet6/in6_pcb.h>
60 #include <netinet/ip_var.h>
61 #include <netinet/tcp.h>
62 #include <netinet/tcp_fsm.h>
63 #include <netinet/tcp_seq.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_msec_to_ticks(SYSCTL_HANDLER_ARGS)
76 tt = *(int *)oidp->oid_arg1;
77 s = (int)((int64_t)tt * 1000 / hz);
79 error = sysctl_handle_int(oidp, &s, 0, req);
80 if (error || !req->newptr)
83 tt = (int)((int64_t)s * hz / 1000);
87 *(int *)oidp->oid_arg1 = tt;
92 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT|CTLFLAG_RW,
93 &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", "");
96 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT|CTLFLAG_RW,
97 &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", "");
100 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT|CTLFLAG_RW,
101 &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", "");
104 SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime,
105 CTLTYPE_INT|CTLFLAG_RW, &tcp_delacktime, 0, sysctl_msec_to_ticks, "I",
106 "Time before a delayed ACK is sent");
109 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW,
110 &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime");
113 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min, CTLTYPE_INT|CTLFLAG_RW,
114 &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I", "Minimum Retransmission Timeout");
117 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop, CTLTYPE_INT|CTLFLAG_RW,
118 &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I", "Retransmission Timer Slop");
120 static int always_keepalive = 0;
121 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW,
122 &always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections");
124 static int tcp_keepcnt = TCPTV_KEEPCNT;
125 /* max idle probes */
126 int tcp_maxpersistidle;
127 /* max idle time in persist */
131 * Tcp protocol timeout routine called every 500 ms.
132 * Updates timestamps used for TCP
133 * causes finite state machine actions if timers expire.
142 tcp_maxidle = tcp_keepcnt * tcp_keepintvl;
148 * Cancel all timers for TCP tp.
154 callout_stop(tp->tt_2msl);
155 callout_stop(tp->tt_persist);
156 callout_stop(tp->tt_keep);
157 callout_stop(tp->tt_rexmt);
160 int tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] =
161 { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 };
163 int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
164 { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
166 static int tcp_totbackoff = 511; /* sum of tcp_backoff[] */
169 * TCP timer processing.
172 tcp_timer_delack(xtp)
175 struct tcpcb *tp = xtp;
179 if (callout_pending(tp->tt_delack) || !callout_active(tp->tt_delack)) {
183 callout_deactivate(tp->tt_delack);
185 tp->t_flags |= TF_ACKNOW;
186 tcpstat.tcps_delack++;
187 (void) tcp_output(tp);
195 struct tcpcb *tp = xtp;
200 ostate = tp->t_state;
203 if (callout_pending(tp->tt_2msl) || !callout_active(tp->tt_2msl)) {
207 callout_deactivate(tp->tt_2msl);
209 * 2 MSL timeout in shutdown went off. If we're closed but
210 * still waiting for peer to close and connection has been idle
211 * too long, or if 2MSL time is up from TIME_WAIT, delete connection
212 * control block. Otherwise, check again in a bit.
214 if (tp->t_state != TCPS_TIME_WAIT &&
215 (ticks - tp->t_rcvtime) <= tcp_maxidle)
216 callout_reset(tp->tt_2msl, tcp_keepintvl,
222 if (tp && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
223 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
233 struct tcpcb *tp = xtp;
234 struct tcptemp *t_template;
239 ostate = tp->t_state;
242 if (callout_pending(tp->tt_keep) || !callout_active(tp->tt_keep)) {
246 callout_deactivate(tp->tt_keep);
248 * Keep-alive timer went off; send something
249 * or drop connection if idle for too long.
251 tcpstat.tcps_keeptimeo++;
252 if (tp->t_state < TCPS_ESTABLISHED)
254 if ((always_keepalive ||
255 tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE) &&
256 tp->t_state <= TCPS_CLOSING) {
257 if ((ticks - tp->t_rcvtime) >= tcp_keepidle + tcp_maxidle)
260 * Send a packet designed to force a response
261 * if the peer is up and reachable:
262 * either an ACK if the connection is still alive,
263 * or an RST if the peer has closed the connection
264 * due to timeout or reboot.
265 * Using sequence number tp->snd_una-1
266 * causes the transmitted zero-length segment
267 * to lie outside the receive window;
268 * by the protocol spec, this requires the
269 * correspondent TCP to respond.
271 tcpstat.tcps_keepprobe++;
272 t_template = tcp_maketemplate(tp);
274 tcp_respond(tp, t_template->tt_ipgen,
275 &t_template->tt_t, (struct mbuf *)NULL,
276 tp->rcv_nxt, tp->snd_una - 1, 0);
277 (void) m_free(dtom(t_template));
279 callout_reset(tp->tt_keep, tcp_keepintvl, tcp_timer_keep, tp);
281 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
284 if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
285 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
292 tcpstat.tcps_keepdrops++;
293 tp = tcp_drop(tp, ETIMEDOUT);
296 if (tp && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
297 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
304 tcp_timer_persist(xtp)
307 struct tcpcb *tp = xtp;
312 ostate = tp->t_state;
315 if (callout_pending(tp->tt_persist) || !callout_active(tp->tt_persist)){
319 callout_deactivate(tp->tt_persist);
321 * Persistance timer into zero window.
322 * Force a byte to be output, if possible.
324 tcpstat.tcps_persisttimeo++;
326 * Hack: if the peer is dead/unreachable, we do not
327 * time out if the window is closed. After a full
328 * backoff, drop the connection if the idle time
329 * (no responses to probes) reaches the maximum
330 * backoff that we would use if retransmitting.
332 if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
333 ((ticks - tp->t_rcvtime) >= tcp_maxpersistidle ||
334 (ticks - tp->t_rcvtime) >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
335 tcpstat.tcps_persistdrop++;
336 tp = tcp_drop(tp, ETIMEDOUT);
341 (void) tcp_output(tp);
346 if (tp && tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
347 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
357 struct tcpcb *tp = xtp;
363 ostate = tp->t_state;
366 if (callout_pending(tp->tt_rexmt) || !callout_active(tp->tt_rexmt)) {
370 callout_deactivate(tp->tt_rexmt);
372 * Retransmission timer went off. Message has not
373 * been acked within retransmit interval. Back off
374 * to a longer retransmit interval and retransmit one segment.
376 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
377 tp->t_rxtshift = TCP_MAXRXTSHIFT;
378 tcpstat.tcps_timeoutdrop++;
379 tp = tcp_drop(tp, tp->t_softerror ?
380 tp->t_softerror : ETIMEDOUT);
383 if (tp->t_rxtshift == 1) {
385 * first retransmit; record ssthresh and cwnd so they can
386 * be recovered if this turns out to be a "bad" retransmit.
387 * A retransmit is considered "bad" if an ACK for this
388 * segment is received within RTT/2 interval; the assumption
389 * here is that the ACK was already in flight. See
390 * "On Estimating End-to-End Network Path Properties" by
391 * Allman and Paxson for more details.
393 tp->snd_cwnd_prev = tp->snd_cwnd;
394 tp->snd_ssthresh_prev = tp->snd_ssthresh;
395 tp->snd_high_prev = tp->snd_high;
396 tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
398 tcpstat.tcps_rexmttimeo++;
399 if (tp->t_state == TCPS_SYN_SENT)
400 rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift];
402 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
403 TCPT_RANGESET(tp->t_rxtcur, rexmt,
404 tp->t_rttmin, TCPTV_REXMTMAX);
406 * Disable rfc1323 and rfc1644 if we havn't got any response to
407 * our third SYN to work-around some broken terminal servers
408 * (most of which have hopefully been retired) that have bad VJ
409 * header compression code which trashes TCP segments containing
410 * unknown-to-them TCP options.
412 if ((tp->t_state == TCPS_SYN_SENT) && (tp->t_rxtshift == 3))
413 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP|TF_REQ_CC);
415 * If losing, let the lower level know and try for
416 * a better route. Also, if we backed off this far,
417 * our srtt estimate is probably bogus. Clobber it
418 * so we'll take the next rtt measurement as our srtt;
419 * move the current srtt into rttvar to keep the current
420 * retransmit times until then.
422 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
424 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
425 in6_losing(tp->t_inpcb);
428 in_losing(tp->t_inpcb);
429 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
432 tp->snd_nxt = tp->snd_una;
433 tp->snd_high = tp->snd_max;
435 * Force a segment to be sent.
437 tp->t_flags |= TF_ACKNOW;
439 * If timing a segment in this window, stop the timer.
443 * Close the congestion window down to one segment
444 * (we'll open it by one segment for each ack we get).
445 * Since we probably have a window's worth of unacked
446 * data accumulated, this "slow start" keeps us from
447 * dumping all that data as back-to-back packets (which
448 * might overwhelm an intermediate gateway).
450 * There are two phases to the opening: Initially we
451 * open by one mss on each ack. This makes the window
452 * size increase exponentially with time. If the
453 * window is larger than the path can handle, this
454 * exponential growth results in dropped packet(s)
455 * almost immediately. To get more time between
456 * drops but still "push" the network to take advantage
457 * of improving conditions, we switch from exponential
458 * to linear window opening at some threshhold size.
459 * For a threshhold, we use half the current window
460 * size, truncated to a multiple of the mss.
462 * (the minimum cwnd that will give us exponential
463 * growth is 2 mss. We don't allow the threshhold
467 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
470 tp->snd_cwnd = tp->t_maxseg;
471 tp->snd_ssthresh = win * tp->t_maxseg;
474 (void) tcp_output(tp);
478 if (tp && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
479 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,