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 #include "iterator/iterator.h" 45 46 /* overwritten by config: infra_cache_min_rtt: */ 47 int RTT_MIN_TIMEOUT = 50; 48 /** calculate RTO from rtt information */ 49 static int 50 calc_rto(const struct rtt_info* rtt) 51 { 52 /* From Stevens, Unix Network Programming, Vol1, 3rd ed., p.598 */ 53 int rto = rtt->srtt + 4*rtt->rttvar; 54 if(rto < RTT_MIN_TIMEOUT) 55 rto = RTT_MIN_TIMEOUT; 56 if(rto > RTT_MAX_TIMEOUT) 57 rto = RTT_MAX_TIMEOUT; 58 return rto; 59 } 60 61 void 62 rtt_init(struct rtt_info* rtt) 63 { 64 rtt->srtt = 0; 65 rtt->rttvar = UNKNOWN_SERVER_NICENESS/4; 66 rtt->rto = calc_rto(rtt); 67 /* default value from the book is 0 + 4*0.75 = 3 seconds */ 68 /* first RTO is 0 + 4*0.094 = 0.376 seconds */ 69 } 70 71 int 72 rtt_timeout(const struct rtt_info* rtt) 73 { 74 return rtt->rto; 75 } 76 77 int 78 rtt_unclamped(const struct rtt_info* rtt) 79 { 80 if(calc_rto(rtt) != rtt->rto) { 81 /* timeout fallback has happened */ 82 return rtt->rto; 83 } 84 /* return unclamped value */ 85 return rtt->srtt + 4*rtt->rttvar; 86 } 87 88 void 89 rtt_update(struct rtt_info* rtt, int ms) 90 { 91 int delta = ms - rtt->srtt; 92 rtt->srtt += delta / 8; /* g = 1/8 */ 93 if(delta < 0) 94 delta = -delta; /* |delta| */ 95 rtt->rttvar += (delta - rtt->rttvar) / 4; /* h = 1/4 */ 96 rtt->rto = calc_rto(rtt); 97 } 98 99 void 100 rtt_lost(struct rtt_info* rtt, int orig) 101 { 102 /* exponential backoff */ 103 104 /* if a query succeeded and put down the rto meanwhile, ignore this */ 105 if(rtt->rto < orig) 106 return; 107 108 /* the original rto is doubled, not the current one to make sure 109 * that the values in the cache are not increased by lots of 110 * queries simultaneously as they time out at the same time */ 111 orig *= 2; 112 if(rtt->rto <= orig) { 113 rtt->rto = orig; 114 if(rtt->rto > RTT_MAX_TIMEOUT) 115 rtt->rto = RTT_MAX_TIMEOUT; 116 } 117 } 118 119 int rtt_notimeout(const struct rtt_info* rtt) 120 { 121 return calc_rto(rtt); 122 } 123