1238106Sdes/* 2238106Sdes * util/rtt.c - UDP round trip time estimator for resend timeouts. 3238106Sdes * 4238106Sdes * Copyright (c) 2007, NLnet Labs. All rights reserved. 5238106Sdes * 6238106Sdes * This software is open source. 7238106Sdes * 8238106Sdes * Redistribution and use in source and binary forms, with or without 9238106Sdes * modification, are permitted provided that the following conditions 10238106Sdes * are met: 11238106Sdes * 12238106Sdes * Redistributions of source code must retain the above copyright notice, 13238106Sdes * this list of conditions and the following disclaimer. 14238106Sdes * 15238106Sdes * Redistributions in binary form must reproduce the above copyright notice, 16238106Sdes * this list of conditions and the following disclaimer in the documentation 17238106Sdes * and/or other materials provided with the distribution. 18238106Sdes * 19238106Sdes * Neither the name of the NLNET LABS nor the names of its contributors may 20238106Sdes * be used to endorse or promote products derived from this software without 21238106Sdes * specific prior written permission. 22238106Sdes * 23238106Sdes * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 24269257Sdes * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 25269257Sdes * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 26269257Sdes * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 27269257Sdes * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 28269257Sdes * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED 29269257Sdes * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 30269257Sdes * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 31269257Sdes * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 32269257Sdes * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 33269257Sdes * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 34238106Sdes */ 35238106Sdes 36238106Sdes/** 37238106Sdes * \file 38238106Sdes * 39238106Sdes * This file contains a data type and functions to help estimate good 40238106Sdes * round trip times for UDP resend timeout values. 41238106Sdes */ 42238106Sdes#include "config.h" 43238106Sdes#include "util/rtt.h" 44238106Sdes 45238106Sdes/** calculate RTO from rtt information */ 46238106Sdesstatic int 47238106Sdescalc_rto(const struct rtt_info* rtt) 48238106Sdes{ 49238106Sdes /* From Stevens, Unix Network Programming, Vol1, 3rd ed., p.598 */ 50238106Sdes int rto = rtt->srtt + 4*rtt->rttvar; 51238106Sdes if(rto < RTT_MIN_TIMEOUT) 52238106Sdes rto = RTT_MIN_TIMEOUT; 53238106Sdes if(rto > RTT_MAX_TIMEOUT) 54238106Sdes rto = RTT_MAX_TIMEOUT; 55238106Sdes return rto; 56238106Sdes} 57238106Sdes 58238106Sdesvoid 59238106Sdesrtt_init(struct rtt_info* rtt) 60238106Sdes{ 61238106Sdes rtt->srtt = 0; 62238106Sdes rtt->rttvar = 94; 63238106Sdes rtt->rto = calc_rto(rtt); 64238106Sdes /* default value from the book is 0 + 4*0.75 = 3 seconds */ 65238106Sdes /* first RTO is 0 + 4*0.094 = 0.376 seconds */ 66238106Sdes} 67238106Sdes 68238106Sdesint 69238106Sdesrtt_timeout(const struct rtt_info* rtt) 70238106Sdes{ 71238106Sdes return rtt->rto; 72238106Sdes} 73238106Sdes 74238106Sdesint 75238106Sdesrtt_unclamped(const struct rtt_info* rtt) 76238106Sdes{ 77238106Sdes if(calc_rto(rtt) != rtt->rto) { 78238106Sdes /* timeout fallback has happened */ 79238106Sdes return rtt->rto; 80238106Sdes } 81238106Sdes /* return unclamped value */ 82238106Sdes return rtt->srtt + 4*rtt->rttvar; 83238106Sdes} 84238106Sdes 85238106Sdesvoid 86238106Sdesrtt_update(struct rtt_info* rtt, int ms) 87238106Sdes{ 88238106Sdes int delta = ms - rtt->srtt; 89238106Sdes rtt->srtt += delta / 8; /* g = 1/8 */ 90238106Sdes if(delta < 0) 91238106Sdes delta = -delta; /* |delta| */ 92238106Sdes rtt->rttvar += (delta - rtt->rttvar) / 4; /* h = 1/4 */ 93238106Sdes rtt->rto = calc_rto(rtt); 94238106Sdes} 95238106Sdes 96238106Sdesvoid 97238106Sdesrtt_lost(struct rtt_info* rtt, int orig) 98238106Sdes{ 99238106Sdes /* exponential backoff */ 100238106Sdes 101238106Sdes /* if a query succeeded and put down the rto meanwhile, ignore this */ 102238106Sdes if(rtt->rto < orig) 103238106Sdes return; 104238106Sdes 105238106Sdes /* the original rto is doubled, not the current one to make sure 106238106Sdes * that the values in the cache are not increased by lots of 107238106Sdes * queries simultaneously as they time out at the same time */ 108238106Sdes orig *= 2; 109238106Sdes if(rtt->rto <= orig) { 110238106Sdes rtt->rto = orig; 111238106Sdes if(rtt->rto > RTT_MAX_TIMEOUT) 112238106Sdes rtt->rto = RTT_MAX_TIMEOUT; 113238106Sdes } 114238106Sdes} 115238106Sdes 116238106Sdesint rtt_notimeout(const struct rtt_info* rtt) 117238106Sdes{ 118238106Sdes return calc_rto(rtt); 119238106Sdes} 120