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 LIMITED 25 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 26 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE 27 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 28 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 29 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 30 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 31 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 32 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 33 * 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 #include "util/log.h" 45 46 /** calculate RTO from rtt information */ 47 static int 48 calc_rto(const struct rtt_info* rtt) 49 { 50 /* From Stevens, Unix Network Programming, Vol1, 3rd ed., p.598 */ 51 int rto = rtt->srtt + 4*rtt->rttvar; 52 if(rto < RTT_MIN_TIMEOUT) 53 rto = RTT_MIN_TIMEOUT; 54 if(rto > RTT_MAX_TIMEOUT) 55 rto = RTT_MAX_TIMEOUT; 56 return rto; 57 } 58 59 void 60 rtt_init(struct rtt_info* rtt) 61 { 62 rtt->srtt = 0; 63 rtt->rttvar = 94; 64 rtt->rto = calc_rto(rtt); 65 /* default value from the book is 0 + 4*0.75 = 3 seconds */ 66 /* first RTO is 0 + 4*0.094 = 0.376 seconds */ 67 } 68 69 int 70 rtt_timeout(const struct rtt_info* rtt) 71 { 72 return rtt->rto; 73 } 74 75 int 76 rtt_unclamped(const struct rtt_info* rtt) 77 { 78 if(calc_rto(rtt) != rtt->rto) { 79 /* timeout fallback has happened */ 80 return rtt->rto; 81 } 82 /* return unclamped value */ 83 return rtt->srtt + 4*rtt->rttvar; 84 } 85 86 void 87 rtt_update(struct rtt_info* rtt, int ms) 88 { 89 int delta = ms - rtt->srtt; 90 rtt->srtt += delta / 8; /* g = 1/8 */ 91 if(delta < 0) 92 delta = -delta; /* |delta| */ 93 rtt->rttvar += (delta - rtt->rttvar) / 4; /* h = 1/4 */ 94 rtt->rto = calc_rto(rtt); 95 } 96 97 void 98 rtt_lost(struct rtt_info* rtt, int orig) 99 { 100 /* exponential backoff */ 101 102 /* if a query succeeded and put down the rto meanwhile, ignore this */ 103 if(rtt->rto < orig) 104 return; 105 106 /* the original rto is doubled, not the current one to make sure 107 * that the values in the cache are not increased by lots of 108 * queries simultaneously as they time out at the same time */ 109 orig *= 2; 110 if(rtt->rto <= orig) { 111 rtt->rto = orig; 112 if(rtt->rto > RTT_MAX_TIMEOUT) 113 rtt->rto = RTT_MAX_TIMEOUT; 114 } 115 } 116 117 int rtt_notimeout(const struct rtt_info* rtt) 118 { 119 return calc_rto(rtt); 120 } 121