The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_timer.h

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    1 /*
    2  * Copyright (c) 1982, 1986, 1993
    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  * 3. All advertising materials mentioning features or use of this software
   14  *    must display the following acknowledgement:
   15  *      This product includes software developed by the University of
   16  *      California, Berkeley and its contributors.
   17  * 4. Neither the name of the University nor the names of its contributors
   18  *    may be used to endorse or promote products derived from this software
   19  *    without specific prior written permission.
   20  *
   21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   31  * SUCH DAMAGE.
   32  *
   33  *      @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
   34  * $FreeBSD: src/sys/netinet/tcp_timer.h,v 1.18.2.1 2002/08/16 22:16:39 dillon Exp $
   35  * $DragonFly: src/sys/netinet/tcp_timer.h,v 1.3 2003/08/23 11:18:00 rob Exp $
   36  */
   37 
   38 #ifndef _NETINET_TCP_TIMER_H_
   39 #define _NETINET_TCP_TIMER_H_
   40 
   41 /*
   42  * The TCPT_REXMT timer is used to force retransmissions.
   43  * The TCP has the TCPT_REXMT timer set whenever segments
   44  * have been sent for which ACKs are expected but not yet
   45  * received.  If an ACK is received which advances tp->snd_una,
   46  * then the retransmit timer is cleared (if there are no more
   47  * outstanding segments) or reset to the base value (if there
   48  * are more ACKs expected).  Whenever the retransmit timer goes off,
   49  * we retransmit one unacknowledged segment, and do a backoff
   50  * on the retransmit timer.
   51  *
   52  * The TCPT_PERSIST timer is used to keep window size information
   53  * flowing even if the window goes shut.  If all previous transmissions
   54  * have been acknowledged (so that there are no retransmissions in progress),
   55  * and the window is too small to bother sending anything, then we start
   56  * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
   57  * we go to transmit state.  Otherwise, at intervals send a single byte
   58  * into the peer's window to force him to update our window information.
   59  * We do this at most as often as TCPT_PERSMIN time intervals,
   60  * but no more frequently than the current estimate of round-trip
   61  * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
   62  * a window update from the peer.
   63  *
   64  * The TCPT_KEEP timer is used to keep connections alive.  If an
   65  * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
   66  * but not yet established, then we drop the connection.  Once the connection
   67  * is established, if the connection is idle for TCPTV_KEEP_IDLE time
   68  * (and keepalives have been enabled on the socket), we begin to probe
   69  * the connection.  We force the peer to send us a segment by sending:
   70  *      <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
   71  * This segment is (deliberately) outside the window, and should elicit
   72  * an ack segment in response from the peer.  If, despite the TCPT_KEEP
   73  * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
   74  * amount of time probing, then we drop the connection.
   75  */
   76 
   77 /*
   78  * Time constants.
   79  */
   80 #define TCPTV_MSL       ( 30*hz)                /* max seg lifetime (hah!) */
   81 #define TCPTV_SRTTBASE  0                       /* base roundtrip time;
   82                                                    if 0, no idea yet */
   83 #define TCPTV_RTOBASE3  (  3*hz)                /* assumed RTO if no info */
   84 #define TCPTV_RTOBASE1  (  1*hz)                /* assumed RTO (RFC 6298) */
   85 #define TCPTV_SRTTDFLT  (  3*hz)                /* assumed RTT if no info */
   86 
   87 #define TCPTV_PERSMIN   (  5*hz)                /* retransmit persistence */
   88 #define TCPTV_PERSMAX   ( 60*hz)                /* maximum persist interval */
   89 
   90 #define TCPTV_KEEP_INIT ( 75*hz)                /* initial connect keepalive */
   91 #define TCPTV_KEEP_IDLE (120*60*hz)             /* dflt time before probing */
   92 #define TCPTV_KEEPINTVL ( 75*hz)                /* default probe interval */
   93 #define TCPTV_KEEPCNT   8                       /* max probes before drop */
   94 
   95 /*
   96  * TCPTV_MIN represents the minimum allowed retransmit interval.  It
   97  * is currently one second but will ultimately be reduced to 3 ticks
   98  * for algorithmic stability, leaving the 200ms variance to deal with
   99  * delayed-acks, protocol overheads.  A 1 second minimum badly breaks
  100  * throughput on any network faster then a modem that has minor but
  101  * continuous packet loss unrelated to congestion, such as on a wireless
  102  * network.
  103  */
  104 #define TCPTV_MIN       ( hz/2 )                /* minimum allowable value */
  105 #define TCPTV_CPU_VAR   ( hz/10)                /* cpu variance (100ms) */
  106 #define TCPTV_REXMTMAX  ( 64*hz)                /* max allowable REXMT value */
  107 
  108 #define TCPTV_TWTRUNC   8                       /* RTO factor to truncate TW */
  109 
  110 #define TCP_LINGERTIME  120                     /* linger at most 2 minutes */
  111 
  112 #define TCP_MAXRXTSHIFT 12                      /* maximum retransmits */
  113 
  114 #define TCPTV_DELACK    (hz / PR_FASTHZ / 2)    /* 100ms timeout */
  115 
  116 #ifdef  TCPTIMERS
  117 static const char *tcptimers[] =
  118     { "REXMT", "PERSIST", "KEEP", "2MSL" };
  119 #endif
  120 
  121 /*
  122  * Force a time value to be in a certain range.
  123  */
  124 #define TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
  125         (tv) = (value) + tcp_rexmit_slop; \
  126         if ((u_long)(tv) < (u_long)(tvmin)) \
  127                 (tv) = (tvmin); \
  128         else if ((u_long)(tv) > (u_long)(tvmax)) \
  129                 (tv) = (tvmax); \
  130 } while(0)
  131 
  132 #ifdef _KERNEL
  133 
  134 #define TCPTV_RTOBASE \
  135         (tcp_low_rtobase ? TCPTV_RTOBASE1 : TCPTV_RTOBASE3)
  136 
  137 struct tcpcb;
  138 struct netmsg_tcp_timer {
  139         struct netmsg_base tt_msg;
  140         struct tcpcb    *tt_tcb;
  141         int             tt_cpuid;               /* owner cpuid */
  142         lwkt_port_t     tt_msgport;             /* owner msgport */
  143         uint32_t        tt_tasks;               /* pending tasks */
  144         uint32_t        tt_running_tasks;       /* running tasks */
  145         uint32_t        tt_prev_tasks;          /* prev pending tasks (debug) */
  146 };
  147 
  148 struct tcp_callout {
  149         struct callout  tc_callout;
  150         uint32_t        tc_task;                /* callout's task id */
  151 };
  152 
  153 extern int tcp_keepinit;                /* time to establish connection */
  154 extern int tcp_keepidle;                /* time before keepalive probes begin */
  155 extern int tcp_keepintvl;               /* time between keepalive probes */
  156 extern int tcp_keepcnt;                 /* maximum number of keepalive probes */
  157 extern int tcp_delacktime;              /* time before sending a delayed ACK */
  158 extern int tcp_maxpersistidle;
  159 extern int tcp_rexmit_min;
  160 extern int tcp_rexmit_slop;
  161 extern int tcp_msl;
  162 extern int tcp_ttl;                     /* time to live for TCP segs */
  163 extern int tcp_backoff[];               /* rxt backoff for data */
  164 extern int tcp_syn_backoff[];           /* rxt backoff for SYN */
  165 extern int tcp_syn_backoff_low[];       /* rxt backoff for SYN w/ RFC6298 */
  166 
  167 void    tcp_timer_2msl(void *xtp);
  168 void    tcp_timer_keep(void *xtp);
  169 void    tcp_timer_persist(void *xtp);
  170 void    tcp_timer_rexmt(void *xtp);
  171 void    tcp_timer_delack(void *xtp);
  172 void    tcp_inittimers(struct tcpcb *);
  173 
  174 struct lwkt_port;
  175 void    tcp_create_timermsg(struct tcpcb *, struct lwkt_port *);
  176 void    tcp_destroy_timermsg(struct tcpcb *);
  177 
  178 #endif /* _KERNEL */
  179 
  180 #endif /* !_NETINET_TCP_TIMER_H_ */

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