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15 * This product includes software developed by the University of
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33 * @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93
34 * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
39 int tcp_keepidle
= TCPTV_KEEP_IDLE
;
40 int tcp_keepintvl
= TCPTV_KEEPINTVL
;
42 int so_options
= DO_KEEPALIVE
;
45 struct tcpstat tcpstat
; /* tcp statistics */
48 u_int32_t tcp_now
; /* for RFC 1323 timestamps */
51 * Fast timeout routine for processing delayed acks
56 register struct socket
*so
;
57 register struct tcpcb
*tp
;
59 DEBUG_CALL("tcp_fasttimo");
63 for (; so
!= &tcb
; so
= so
->so_next
)
64 if ((tp
= (struct tcpcb
*)so
->so_tcpcb
) &&
65 (tp
->t_flags
& TF_DELACK
)) {
66 tp
->t_flags
&= ~TF_DELACK
;
67 tp
->t_flags
|= TF_ACKNOW
;
68 STAT(tcpstat
.tcps_delack
++);
69 (void) tcp_output(tp
);
74 * Tcp protocol timeout routine called every 500 ms.
75 * Updates the timers in all active tcb's and
76 * causes finite state machine actions if timers expire.
81 register struct socket
*ip
, *ipnxt
;
82 register struct tcpcb
*tp
;
85 DEBUG_CALL("tcp_slowtimo");
87 tcp_maxidle
= TCPTV_KEEPCNT
* tcp_keepintvl
;
89 * Search through tcb's and update active timers.
94 for (; ip
!= &tcb
; ip
= ipnxt
) {
99 for (i
= 0; i
< TCPT_NTIMERS
; i
++) {
100 if (tp
->t_timer
[i
] && --tp
->t_timer
[i
] == 0) {
102 if (ipnxt
->so_prev
!= ip
)
112 tcp_iss
+= TCP_ISSINCR
/PR_SLOWHZ
; /* increment iss */
114 if ((int)tcp_iss
< 0)
115 tcp_iss
= 0; /* XXX */
117 tcp_now
++; /* for timestamps */
121 * Cancel all timers for TCP tp.
129 for (i
= 0; i
< TCPT_NTIMERS
; i
++)
133 int tcp_backoff
[TCP_MAXRXTSHIFT
+ 1] =
134 { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
137 * TCP timer processing.
140 tcp_timers(tp
, timer
)
141 register struct tcpcb
*tp
;
146 DEBUG_CALL("tcp_timers");
151 * 2 MSL timeout in shutdown went off. If we're closed but
152 * still waiting for peer to close and connection has been idle
153 * too long, or if 2MSL time is up from TIME_WAIT, delete connection
154 * control block. Otherwise, check again in a bit.
157 if (tp
->t_state
!= TCPS_TIME_WAIT
&&
158 tp
->t_idle
<= tcp_maxidle
)
159 tp
->t_timer
[TCPT_2MSL
] = tcp_keepintvl
;
165 * Retransmission timer went off. Message has not
166 * been acked within retransmit interval. Back off
167 * to a longer retransmit interval and retransmit one segment.
172 * XXXXX If a packet has timed out, then remove all the queued
173 * packets for that session.
176 if (++tp
->t_rxtshift
> TCP_MAXRXTSHIFT
) {
178 * This is a hack to suit our terminal server here at the uni of canberra
179 * since they have trouble with zeroes... It usually lets them through
180 * unharmed, but under some conditions, it'll eat the zeros. If we
181 * keep retransmitting it, it'll keep eating the zeroes, so we keep
182 * retransmitting, and eventually the connection dies...
183 * (this only happens on incoming data)
185 * So, if we were gonna drop the connection from too many retransmits,
186 * don't... instead halve the t_maxseg, which might break up the NULLs and
193 if (tp
->t_maxseg
< 32) {
195 * We tried our best, now the connection must die!
197 tp
->t_rxtshift
= TCP_MAXRXTSHIFT
;
198 STAT(tcpstat
.tcps_timeoutdrop
++);
199 tp
= tcp_drop(tp
, tp
->t_softerror
);
200 /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
201 return (tp
); /* XXX */
205 * Set rxtshift to 6, which is still at the maximum
210 STAT(tcpstat
.tcps_rexmttimeo
++);
211 rexmt
= TCP_REXMTVAL(tp
) * tcp_backoff
[tp
->t_rxtshift
];
212 TCPT_RANGESET(tp
->t_rxtcur
, rexmt
,
213 (short)tp
->t_rttmin
, TCPTV_REXMTMAX
); /* XXX */
214 tp
->t_timer
[TCPT_REXMT
] = tp
->t_rxtcur
;
216 * If losing, let the lower level know and try for
217 * a better route. Also, if we backed off this far,
218 * our srtt estimate is probably bogus. Clobber it
219 * so we'll take the next rtt measurement as our srtt;
220 * move the current srtt into rttvar to keep the current
221 * retransmit times until then.
223 if (tp
->t_rxtshift
> TCP_MAXRXTSHIFT
/ 4) {
224 /* in_losing(tp->t_inpcb); */
225 tp
->t_rttvar
+= (tp
->t_srtt
>> TCP_RTT_SHIFT
);
228 tp
->snd_nxt
= tp
->snd_una
;
230 * If timing a segment in this window, stop the timer.
234 * Close the congestion window down to one segment
235 * (we'll open it by one segment for each ack we get).
236 * Since we probably have a window's worth of unacked
237 * data accumulated, this "slow start" keeps us from
238 * dumping all that data as back-to-back packets (which
239 * might overwhelm an intermediate gateway).
241 * There are two phases to the opening: Initially we
242 * open by one mss on each ack. This makes the window
243 * size increase exponentially with time. If the
244 * window is larger than the path can handle, this
245 * exponential growth results in dropped packet(s)
246 * almost immediately. To get more time between
247 * drops but still "push" the network to take advantage
248 * of improving conditions, we switch from exponential
249 * to linear window opening at some threshold size.
250 * For a threshold, we use half the current window
251 * size, truncated to a multiple of the mss.
253 * (the minimum cwnd that will give us exponential
254 * growth is 2 mss. We don't allow the threshold
258 u_int win
= min(tp
->snd_wnd
, tp
->snd_cwnd
) / 2 / tp
->t_maxseg
;
261 tp
->snd_cwnd
= tp
->t_maxseg
;
262 tp
->snd_ssthresh
= win
* tp
->t_maxseg
;
265 (void) tcp_output(tp
);
269 * Persistence timer into zero window.
270 * Force a byte to be output, if possible.
273 STAT(tcpstat
.tcps_persisttimeo
++);
276 (void) tcp_output(tp
);
281 * Keep-alive timer went off; send something
282 * or drop connection if idle for too long.
285 STAT(tcpstat
.tcps_keeptimeo
++);
286 if (tp
->t_state
< TCPS_ESTABLISHED
)
289 /* if (tp->t_socket->so_options & SO_KEEPALIVE && */
290 if ((so_options
) && tp
->t_state
<= TCPS_CLOSE_WAIT
) {
291 if (tp
->t_idle
>= tcp_keepidle
+ tcp_maxidle
)
294 * Send a packet designed to force a response
295 * if the peer is up and reachable:
296 * either an ACK if the connection is still alive,
297 * or an RST if the peer has closed the connection
298 * due to timeout or reboot.
299 * Using sequence number tp->snd_una-1
300 * causes the transmitted zero-length segment
301 * to lie outside the receive window;
302 * by the protocol spec, this requires the
303 * correspondent TCP to respond.
305 STAT(tcpstat
.tcps_keepprobe
++);
308 * The keepalive packet must have nonzero length
309 * to get a 4.2 host to respond.
311 tcp_respond(tp
, &tp
->t_template
, (struct mbuf
*)NULL
,
312 tp
->rcv_nxt
- 1, tp
->snd_una
- 1, 0);
314 tcp_respond(tp
, &tp
->t_template
, (struct mbuf
*)NULL
,
315 tp
->rcv_nxt
, tp
->snd_una
- 1, 0);
317 tp
->t_timer
[TCPT_KEEP
] = tcp_keepintvl
;
319 tp
->t_timer
[TCPT_KEEP
] = tcp_keepidle
;
323 STAT(tcpstat
.tcps_keepdrops
++);
324 tp
= tcp_drop(tp
, 0); /* ETIMEDOUT); */