unbound/util/rtt.c

   1 /*
   2  * util/rtt.c - UDP round trip time estimator for resend timeouts.
   3  *
   4  * Copyright (c) 2007, NLnet Labs. All rights reserved.
   5  *
   6  * This software is open source.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  *
  12  * Redistributions of source code must retain the above copyright notice,
  13  * this list of conditions and the following disclaimer.
  14  *
  15  * Redistributions in binary form must reproduce the above copyright notice,
  16  * this list of conditions and the following disclaimer in the documentation
  17  * and/or other materials provided with the distribution.
  18  *
  19  * Neither the name of the NLNET LABS nor the names of its contributors may
  20  * be used to endorse or promote products derived from this software without
  21  * specific prior written permission.
  22  *
  23  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  24  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  25  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  26  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  27  * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  28  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
  29  * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  30  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  31  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  32  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  33  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  34  */
  35
  36 /**
  37  * \file
  38  *
  39  * This file contains a data type and functions to help estimate good
  40  * round trip times for UDP resend timeout values.
  41  */
  42 #include "config.h"
  43 #include "util/rtt.h"
  44
  45 /** calculate RTO from rtt information */
  46 static int
  47 calc_rto(const struct rtt_info* rtt)
  48 {
  49         /* From Stevens, Unix Network Programming, Vol1, 3rd ed., p.598 */
  50         int rto = rtt->srtt + 4*rtt->rttvar;
  51         if(rto < RTT_MIN_TIMEOUT)
  52                 rto = RTT_MIN_TIMEOUT;
  53         if(rto > RTT_MAX_TIMEOUT)
  54                 rto = RTT_MAX_TIMEOUT;
  55         return rto;
  56 }
  57
  58 void
  59 rtt_init(struct rtt_info* rtt)
  60 {
  61         rtt->srtt = 0;
  62         rtt->rttvar = 94;
  63         rtt->rto = calc_rto(rtt);
  64         /* default value from the book is 0 + 4*0.75 = 3 seconds */
  65         /* first RTO is 0 + 4*0.094 = 0.376 seconds */
  66 }
  67
  68 int
  69 rtt_timeout(const struct rtt_info* rtt)
  70 {
  71         return rtt->rto;
  72 }
  73
  74 int
  75 rtt_unclamped(const struct rtt_info* rtt)
  76 {
  77         if(calc_rto(rtt) != rtt->rto) {
  78                 /* timeout fallback has happened */
  79                 return rtt->rto;
  80         }
  81         /* return unclamped value */
  82         return rtt->srtt + 4*rtt->rttvar;
  83 }
  84
  85 void
  86 rtt_update(struct rtt_info* rtt, int ms)
  87 {
  88         int delta = ms - rtt->srtt;
  89         rtt->srtt += delta / 8; /* g = 1/8 */
  90         if(delta < 0)
  91                 delta = -delta; /* |delta| */
  92         rtt->rttvar += (delta - rtt->rttvar) / 4; /* h = 1/4 */
  93         rtt->rto = calc_rto(rtt);
  94 }
  95
  96 void
  97 rtt_lost(struct rtt_info* rtt, int orig)
  98 {
  99         /* exponential backoff */
 100
 101         /* if a query succeeded and put down the rto meanwhile, ignore this */
 102         if(rtt->rto < orig)
 103                 return;
 104
 105         /* the original rto is doubled, not the current one to make sure
 106          * that the values in the cache are not increased by lots of
 107          * queries simultaneously as they time out at the same time */
 108         orig *= 2;
 109         if(rtt->rto <= orig) {
 110                 rtt->rto = orig;
 111                 if(rtt->rto > RTT_MAX_TIMEOUT)
 112                         rtt->rto = RTT_MAX_TIMEOUT;
 113         }
 114 }
 115
 116 int rtt_notimeout(const struct rtt_info* rtt)
 117 {
 118         return calc_rto(rtt);
 119 }