timer.c revision 1244480976d357447aeddd3f44977586bfa0462b 
1/*
2 * linux/net/sunrpc/timer.c
3 *
4 * Estimate RPC request round trip time.
5 *
6 * Based on packet round-trip and variance estimator algorithms described
7 * in appendix A of "Congestion Avoidance and Control" by Van Jacobson
8 * and Michael J. Karels (ACM Computer Communication Review; Proceedings
9 * of the Sigcomm '88 Symposium in Stanford, CA, August, 1988).
10 *
11 * This RTT estimator is used only for RPC over datagram protocols.
12 *
13 * Copyright (C) 2002 Trond Myklebust <trond.myklebust@fys.uio.no>
14 */
15
16#include <asm/param.h>
17
18#include <linux/types.h>
19#include <linux/unistd.h>
20#include <linux/module.h>
21
22#include <linux/sunrpc/clnt.h>
23
24#define RPC_RTO_MAX (60*HZ)
25#define RPC_RTO_INIT (HZ/5)
26#define RPC_RTO_MIN (HZ/10)
27
28void
29rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo)
30{
31	unsigned long init = 0;
32	unsigned i;
33
34	rt->timeo = timeo;
35
36	if (timeo > RPC_RTO_INIT)
37		init = (timeo - RPC_RTO_INIT) << 3;
38	for (i = 0; i < 5; i++) {
39		rt->srtt[i] = init;
40		rt->sdrtt[i] = RPC_RTO_INIT;
41		rt->ntimeouts[i] = 0;
42	}
43}
44EXPORT_SYMBOL_GPL(rpc_init_rtt);
45
46/*
47 * NB: When computing the smoothed RTT and standard deviation,
48 *     be careful not to produce negative intermediate results.
49 */
50void
51rpc_update_rtt(struct rpc_rtt *rt, unsigned timer, long m)
52{
53	long *srtt, *sdrtt;
54
55	if (timer-- == 0)
56		return;
57
58	/* jiffies wrapped; ignore this one */
59	if (m < 0)
60		return;
61
62	if (m == 0)
63		m = 1L;
64
65	srtt = (long *)&rt->srtt[timer];
66	m -= *srtt >> 3;
67	*srtt += m;
68
69	if (m < 0)
70		m = -m;
71
72	sdrtt = (long *)&rt->sdrtt[timer];
73	m -= *sdrtt >> 2;
74	*sdrtt += m;
75
76	/* Set lower bound on the variance */
77	if (*sdrtt < RPC_RTO_MIN)
78		*sdrtt = RPC_RTO_MIN;
79}
80EXPORT_SYMBOL_GPL(rpc_update_rtt);
81
82/*
83 * Estimate rto for an nfs rpc sent via. an unreliable datagram.
84 * Use the mean and mean deviation of rtt for the appropriate type of rpc
85 * for the frequent rpcs and a default for the others.
86 * The justification for doing "other" this way is that these rpcs
87 * happen so infrequently that timer est. would probably be stale.
88 * Also, since many of these rpcs are
89 * non-idempotent, a conservative timeout is desired.
90 * getattr, lookup,
91 * read, write, commit     - A+4D
92 * other                   - timeo
93 */
94
95unsigned long
96rpc_calc_rto(struct rpc_rtt *rt, unsigned timer)
97{
98	unsigned long res;
99
100	if (timer-- == 0)
101		return rt->timeo;
102
103	res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];
104	if (res > RPC_RTO_MAX)
105		res = RPC_RTO_MAX;
106
107	return res;
108}
109EXPORT_SYMBOL_GPL(rpc_calc_rto);
110