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31 * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
35 #ifndef _NETINET_TCP_TIMER_H_
36 #define _NETINET_TCP_TIMER_H_
39 * The TCPT_REXMT timer is used to force retransmissions.
40 * The TCP has the TCPT_REXMT timer set whenever segments
41 * have been sent for which ACKs are expected but not yet
42 * received. If an ACK is received which advances tp->snd_una,
43 * then the retransmit timer is cleared (if there are no more
44 * outstanding segments) or reset to the base value (if there
45 * are more ACKs expected). Whenever the retransmit timer goes off,
46 * we retransmit one unacknowledged segment, and do a backoff
47 * on the retransmit timer.
49 * The TCPT_PERSIST timer is used to keep window size information
50 * flowing even if the window goes shut. If all previous transmissions
51 * have been acknowledged (so that there are no retransmissions in progress),
52 * and the window is too small to bother sending anything, then we start
53 * the TCPT_PERSIST timer. When it expires, if the window is nonzero,
54 * we go to transmit state. Otherwise, at intervals send a single byte
55 * into the peer's window to force him to update our window information.
56 * We do this at most as often as TCPT_PERSMIN time intervals,
57 * but no more frequently than the current estimate of round-trip
58 * packet time. The TCPT_PERSIST timer is cleared whenever we receive
59 * a window update from the peer.
61 * The TCPT_KEEP timer is used to keep connections alive. If an
62 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
63 * but not yet established, then we drop the connection. Once the connection
64 * is established, if the connection is idle for TCPTV_KEEP_IDLE time
65 * (and keepalives have been enabled on the socket), we begin to probe
66 * the connection. We force the peer to send us a segment by sending:
67 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
68 * This segment is (deliberately) outside the window, and should elicit
69 * an ack segment in response from the peer. If, despite the TCPT_KEEP
70 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
71 * amount of time probing, then we drop the connection.
77 #define TCPTV_MSL ( 30*hz) /* max seg lifetime (hah!) */
78 #define TCPTV_SRTTBASE 0 /* base roundtrip time;
80 #define TCPTV_RTOBASE ( 1*hz) /* assumed RTO if no info */
82 #define TCPTV_PERSMIN ( 5*hz) /* minimum persist interval */
83 #define TCPTV_PERSMAX ( 60*hz) /* maximum persist interval */
85 #define TCPTV_KEEP_INIT ( 75*hz) /* initial connect keepalive */
86 #define TCPTV_KEEP_IDLE (120*60*hz) /* dflt time before probing */
87 #define TCPTV_KEEPINTVL ( 75*hz) /* default probe interval */
88 #define TCPTV_KEEPCNT 8 /* max probes before drop */
89 #define TCPTV_MAXUNACKTIME 0 /* max time without making progress */
91 #define TCPTV_FINWAIT2_TIMEOUT (60*hz) /* FIN_WAIT_2 timeout if no receiver */
94 * Minimum retransmit timer is 3 ticks, for algorithmic stability.
95 * TCPT_RANGESET() will add another TCPTV_CPU_VAR to deal with
96 * the expected worst-case processing variances by the kernels
97 * representing the end points. Such variances do not always show
98 * up in the srtt because the timestamp is often calculated at
99 * the interface rather then at the TCP layer. This value is
100 * typically 50ms. However, it is also possible that delayed
101 * acks (typically 100ms) could create issues so we set the slop
102 * to 200ms to try to cover it. Note that, properly speaking,
103 * delayed-acks should not create a major issue for interactive
104 * environments which 'P'ush the last segment, at least as
105 * long as implementations do the required 'at least one ack
106 * for every two packets' for the non-interactive streaming case.
107 * (maybe the RTO calculation should use 2*RTT instead of RTT
108 * to handle the ack-every-other-packet case).
110 * The prior minimum of 1*hz (1 second) badly breaks throughput on any
111 * networks faster then a modem that has minor (e.g. 1%) packet loss.
113 #define TCPTV_MIN ( hz/33 ) /* minimum allowable value */
114 #define TCPTV_CPU_VAR ( hz/5 ) /* cpu variance allowed (200ms) */
115 #define TCPTV_REXMTMAX ( 64*hz) /* max allowable REXMT value */
117 #define TCPTV_TWTRUNC 8 /* RTO factor to truncate TW */
119 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
121 #define TCPTV_DELACK ( hz/25 ) /* 40ms timeout */
124 * If we exceed this number of retransmits for a single segment, we'll consider
125 * the current srtt measurement no longer valid and will recalculate from
126 * scratch starting with the next ACK.
128 #define TCP_RTT_INVALIDATE (TCP_MAXRXTSHIFT / 4)
131 static const char *tcptimers[] =
132 { "REXMT", "PERSIST", "KEEP", "2MSL", "DELACK" };
136 * Force a time value to be in a certain range.
138 #define TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
139 (tv) = (value) + tcp_rexmit_slop; \
140 if ((u_long)(tv) < (u_long)(tvmin)) \
142 if ((u_long)(tv) > (u_long)(tvmax)) \
151 struct callout tt_rexmt; /* retransmit timer */
152 struct callout tt_persist; /* retransmit persistence */
153 struct callout tt_keep; /* keepalive */
154 struct callout tt_2msl; /* 2*msl TIME_WAIT timer */
155 struct callout tt_delack; /* delayed ACK timer */
156 uint32_t tt_flags; /* Timers flags */
157 uint32_t tt_draincnt; /* Count being drained */
161 * Flags for the tt_flags field.
163 #define TT_DELACK 0x0001
164 #define TT_REXMT 0x0002
165 #define TT_PERSIST 0x0004
166 #define TT_KEEP 0x0008
167 #define TT_2MSL 0x0010
168 #define TT_MASK (TT_DELACK|TT_REXMT|TT_PERSIST|TT_KEEP|TT_2MSL)
171 * Suspend flags - used when suspending a timer
172 * from ever running again.
174 #define TT_DELACK_SUS 0x0100
175 #define TT_REXMT_SUS 0x0200
176 #define TT_PERSIST_SUS 0x0400
177 #define TT_KEEP_SUS 0x0800
178 #define TT_2MSL_SUS 0x1000
180 #define TT_STOPPED 0x00010000
182 #define TP_KEEPINIT(tp) ((tp)->t_keepinit ? (tp)->t_keepinit : tcp_keepinit)
183 #define TP_KEEPIDLE(tp) ((tp)->t_keepidle ? (tp)->t_keepidle : tcp_keepidle)
184 #define TP_KEEPINTVL(tp) ((tp)->t_keepintvl ? (tp)->t_keepintvl : tcp_keepintvl)
185 #define TP_KEEPCNT(tp) ((tp)->t_keepcnt ? (tp)->t_keepcnt : tcp_keepcnt)
186 #define TP_MAXIDLE(tp) (TP_KEEPCNT(tp) * TP_KEEPINTVL(tp))
187 #define TP_MAXUNACKTIME(tp) \
188 ((tp)->t_maxunacktime ? (tp)->t_maxunacktime : tcp_maxunacktime)
191 * Obtain the time until the restransmit timer should fire.
192 * This macro ensures the restransmit timer fires at the earlier of the
193 * t_rxtcur value or the time the maxunacktime would be exceeded.
195 #define TP_RXTCUR(tp) \
196 ((TP_MAXUNACKTIME(tp) == 0 || tp->t_acktime == 0) ? tp->t_rxtcur : \
197 max(1, min(tp->t_rxtcur, tp->t_acktime + TP_MAXUNACKTIME(tp) - ticks)))
199 extern int tcp_persmin; /* minimum persist interval */
200 extern int tcp_persmax; /* maximum persist interval */
201 extern int tcp_keepinit; /* time to establish connection */
202 extern int tcp_keepidle; /* time before keepalive probes begin */
203 extern int tcp_keepintvl; /* time between keepalive probes */
204 extern int tcp_keepcnt; /* number of keepalives */
205 extern int tcp_delacktime; /* time before sending a delayed ACK */
206 extern int tcp_maxunacktime; /* max time without making progress */
207 extern int tcp_maxpersistidle;
208 extern int tcp_rexmit_initial;
209 extern int tcp_rexmit_min;
210 extern int tcp_rexmit_slop;
211 extern int tcp_ttl; /* time to live for TCP segs */
212 extern int tcp_backoff[];
213 extern int tcp_totbackoff;
214 extern int tcp_rexmit_drop_options;
216 extern int tcp_finwait2_timeout;
217 extern int tcp_fast_finwait2_recycle;
219 VNET_DECLARE(int, tcp_always_keepalive);
220 #define V_tcp_always_keepalive VNET(tcp_always_keepalive)
221 VNET_DECLARE(int, tcp_pmtud_blackhole_detect);
222 #define V_tcp_pmtud_blackhole_detect VNET(tcp_pmtud_blackhole_detect)
223 VNET_DECLARE(int, tcp_pmtud_blackhole_mss);
224 #define V_tcp_pmtud_blackhole_mss VNET(tcp_pmtud_blackhole_mss)
225 VNET_DECLARE(int, tcp_v6pmtud_blackhole_mss);
226 #define V_tcp_v6pmtud_blackhole_mss VNET(tcp_v6pmtud_blackhole_mss)
227 VNET_DECLARE(int, tcp_msl);
228 #define V_tcp_msl VNET(tcp_msl)
230 void tcp_timer_init(void);
231 void tcp_timer_2msl(void *xtp);
232 void tcp_timer_keep(void *xtp);
233 void tcp_timer_persist(void *xtp);
234 void tcp_timer_rexmt(void *xtp);
235 void tcp_timer_delack(void *xtp);
239 #endif /* !_NETINET_TCP_TIMER_H_ */