2 * util/rtt.c - UDP round trip time estimator for resend timeouts.
4 * Copyright (c) 2007, NLnet Labs. All rights reserved.
6 * This software is open source.
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9 * modification, are permitted provided that the following conditions
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13 * this list of conditions and the following disclaimer.
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16 * this list of conditions and the following disclaimer in the documentation
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24 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
25 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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27 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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29 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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39 * This file contains a data type and functions to help estimate good
40 * round trip times for UDP resend timeout values.
44 #include "iterator/iterator.h"
46 /* overwritten by config: infra_cache_min_rtt: */
47 int RTT_MIN_TIMEOUT = 50;
48 /** calculate RTO from rtt information */
50 calc_rto(const struct rtt_info* rtt)
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;
62 rtt_init(struct rtt_info* rtt)
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 */
72 rtt_timeout(const struct rtt_info* rtt)
78 rtt_unclamped(const struct rtt_info* rtt)
80 if(calc_rto(rtt) != rtt->rto) {
81 /* timeout fallback has happened */
84 /* return unclamped value */
85 return rtt->srtt + 4*rtt->rttvar;
89 rtt_update(struct rtt_info* rtt, int ms)
91 int delta = ms - rtt->srtt;
92 rtt->srtt += delta / 8; /* g = 1/8 */
94 delta = -delta; /* |delta| */
95 rtt->rttvar += (delta - rtt->rttvar) / 4; /* h = 1/4 */
96 rtt->rto = calc_rto(rtt);
100 rtt_lost(struct rtt_info* rtt, int orig)
102 /* exponential backoff */
104 /* if a query succeeded and put down the rto meanwhile, ignore this */
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 */
112 if(rtt->rto <= orig) {
114 if(rtt->rto > RTT_MAX_TIMEOUT)
115 rtt->rto = RTT_MAX_TIMEOUT;
119 int rtt_notimeout(const struct rtt_info* rtt)
121 return calc_rto(rtt);