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 /* overwritten by config: infra_cache_max_rtt: */
49 int RTT_MAX_TIMEOUT = 120000;
50
51 /** calculate RTO from rtt information */
52 static int
calc_rto(const struct rtt_info * rtt)53 calc_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
64 void
rtt_init(struct rtt_info * rtt)65 rtt_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
74 int
rtt_timeout(const struct rtt_info * rtt)75 rtt_timeout(const struct rtt_info* rtt)
76 {
77 return rtt->rto;
78 }
79
80 int
rtt_unclamped(const struct rtt_info * rtt)81 rtt_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
91 void
rtt_update(struct rtt_info * rtt,int ms)92 rtt_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
102 void
rtt_lost(struct rtt_info * rtt,int orig)103 rtt_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
rtt_notimeout(const struct rtt_info * rtt)122 int rtt_notimeout(const struct rtt_info* rtt)
123 {
124 return calc_rto(rtt);
125 }
126