xref: /freebsd/contrib/unbound/util/rtt.c (revision 9768746b)
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
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
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
75 rtt_timeout(const struct rtt_info* rtt)
76 {
77 	return rtt->rto;
78 }
79 
80 int
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
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
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 
122 int rtt_notimeout(const struct rtt_info* rtt)
123 {
124 	return calc_rto(rtt);
125 }
126