120 lines
3.4 KiB
C
120 lines
3.4 KiB
C
/*
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* util/rtt.c - UDP round trip time estimator for resend timeouts.
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*
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* Copyright (c) 2007, NLnet Labs. All rights reserved.
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*
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* This software is open source.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* Neither the name of the NLNET LABS nor the names of its contributors may
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* be used to endorse or promote products derived from this software without
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* specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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/**
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* \file
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*
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* This file contains a data type and functions to help estimate good
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* round trip times for UDP resend timeout values.
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*/
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#include "config.h"
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#include "util/rtt.h"
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/** calculate RTO from rtt information */
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static int
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calc_rto(const struct rtt_info* rtt)
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{
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/* From Stevens, Unix Network Programming, Vol1, 3rd ed., p.598 */
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int rto = rtt->srtt + 4*rtt->rttvar;
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if(rto < RTT_MIN_TIMEOUT)
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rto = RTT_MIN_TIMEOUT;
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if(rto > RTT_MAX_TIMEOUT)
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rto = RTT_MAX_TIMEOUT;
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return rto;
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}
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void
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rtt_init(struct rtt_info* rtt)
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{
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rtt->srtt = 0;
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rtt->rttvar = 94;
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rtt->rto = calc_rto(rtt);
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/* default value from the book is 0 + 4*0.75 = 3 seconds */
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/* first RTO is 0 + 4*0.094 = 0.376 seconds */
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}
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int
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rtt_timeout(const struct rtt_info* rtt)
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{
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return rtt->rto;
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}
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int
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rtt_unclamped(const struct rtt_info* rtt)
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{
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if(calc_rto(rtt) != rtt->rto) {
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/* timeout fallback has happened */
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return rtt->rto;
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}
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/* return unclamped value */
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return rtt->srtt + 4*rtt->rttvar;
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}
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void
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rtt_update(struct rtt_info* rtt, int ms)
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{
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int delta = ms - rtt->srtt;
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rtt->srtt += delta / 8; /* g = 1/8 */
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if(delta < 0)
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delta = -delta; /* |delta| */
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rtt->rttvar += (delta - rtt->rttvar) / 4; /* h = 1/4 */
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rtt->rto = calc_rto(rtt);
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}
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void
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rtt_lost(struct rtt_info* rtt, int orig)
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{
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/* exponential backoff */
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/* if a query succeeded and put down the rto meanwhile, ignore this */
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if(rtt->rto < orig)
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return;
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/* the original rto is doubled, not the current one to make sure
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* that the values in the cache are not increased by lots of
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* queries simultaneously as they time out at the same time */
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orig *= 2;
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if(rtt->rto <= orig) {
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rtt->rto = orig;
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if(rtt->rto > RTT_MAX_TIMEOUT)
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rtt->rto = RTT_MAX_TIMEOUT;
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}
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}
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int rtt_notimeout(const struct rtt_info* rtt)
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{
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return calc_rto(rtt);
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}
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