rtt.c revision 356345 
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: */
47int RTT_MIN_TIMEOUT = 50;
48/** calculate RTO from rtt information */
49static int
50calc_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
61void
62rtt_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
71int
72rtt_timeout(const struct rtt_info* rtt)
73{
74	return rtt->rto;
75}
76
77int
78rtt_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
88void
89rtt_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
99void
100rtt_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
119int rtt_notimeout(const struct rtt_info* rtt)
120{
121	return calc_rto(rtt);
122}
123