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 /** calculate RTO from rtt information */
49 static int
calc_rto(const struct rtt_info * rtt)50 calc_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
61 void
rtt_init(struct rtt_info * rtt)62 rtt_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
71 int
rtt_timeout(const struct rtt_info * rtt)72 rtt_timeout(const struct rtt_info* rtt)
73 {
74 return rtt->rto;
75 }
76
77 int
rtt_unclamped(const struct rtt_info * rtt)78 rtt_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
88 void
rtt_update(struct rtt_info * rtt,int ms)89 rtt_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
99 void
rtt_lost(struct rtt_info * rtt,int orig)100 rtt_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
rtt_notimeout(const struct rtt_info * rtt)119 int rtt_notimeout(const struct rtt_info* rtt)
120 {
121 return calc_rto(rtt);
122 }
123