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 } 120