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/* overwritten by config: infra_cache_max_rtt: */
49int RTT_MAX_TIMEOUT = 120000;
50
51/** calculate RTO from rtt information */
52static int
53calc_rto(const struct rtt_info* rtt)
54{
55	/* From Stevens, Unix Network Programming, Vol1, 3rd ed., p.598 */
56	int rto = rtt->srtt + 4*rtt->rttvar;
57	if(rto < RTT_MIN_TIMEOUT)
58		rto = RTT_MIN_TIMEOUT;
59	if(rto > RTT_MAX_TIMEOUT)
60		rto = RTT_MAX_TIMEOUT;
61	return rto;
62}
63
64void
65rtt_init(struct rtt_info* rtt)
66{
67	rtt->srtt = 0;
68	rtt->rttvar = UNKNOWN_SERVER_NICENESS/4;
69	rtt->rto = calc_rto(rtt);
70	/* default value from the book is 0 + 4*0.75 = 3 seconds */
71	/* first RTO is 0 + 4*0.094 = 0.376 seconds */
72}
73
74int
75rtt_timeout(const struct rtt_info* rtt)
76{
77	return rtt->rto;
78}
79
80int
81rtt_unclamped(const struct rtt_info* rtt)
82{
83	if(calc_rto(rtt) != rtt->rto) {
84		/* timeout fallback has happened */
85		return rtt->rto;
86	}
87	/* return unclamped value */
88	return rtt->srtt + 4*rtt->rttvar;
89}
90
91void
92rtt_update(struct rtt_info* rtt, int ms)
93{
94	int delta = ms - rtt->srtt;
95	rtt->srtt += delta / 8; /* g = 1/8 */
96	if(delta < 0)
97		delta = -delta; /* |delta| */
98	rtt->rttvar += (delta - rtt->rttvar) / 4; /* h = 1/4 */
99	rtt->rto = calc_rto(rtt);
100}
101
102void
103rtt_lost(struct rtt_info* rtt, int orig)
104{
105	/* exponential backoff */
106
107	/* if a query succeeded and put down the rto meanwhile, ignore this */
108	if(rtt->rto < orig)
109		return;
110
111	/* the original rto is doubled, not the current one to make sure
112	 * that the values in the cache are not increased by lots of
113	 * queries simultaneously as they time out at the same time */
114	orig *= 2;
115	if(rtt->rto <= orig) {
116		rtt->rto = orig;
117		if(rtt->rto > RTT_MAX_TIMEOUT)
118			rtt->rto = RTT_MAX_TIMEOUT;
119	}
120}
121
122int rtt_notimeout(const struct rtt_info* rtt)
123{
124	return calc_rto(rtt);
125}
126