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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
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
21#include <linux/sunrpc/clnt.h>
22#include <linux/sunrpc/xprt.h>
23#include <linux/sunrpc/timer.h>
24
25#define RPC_RTO_MAX (60*HZ)
26#define RPC_RTO_INIT (HZ/5)
27#define RPC_RTO_MIN (HZ/10)
28
29void
30rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo)
31{
32 unsigned long init = 0;
33 unsigned i;
34
35 rt->timeo = timeo;
36
37 if (timeo > RPC_RTO_INIT)
38 init = (timeo - RPC_RTO_INIT) << 3;
39 for (i = 0; i < 5; i++) {
40 rt->srtt[i] = init;
41 rt->sdrtt[i] = RPC_RTO_INIT;
42 rt->ntimeouts[i] = 0;
43 }
44}
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}
80
81/*
82 * Estimate rto for an nfs rpc sent via. an unreliable datagram.
83 * Use the mean and mean deviation of rtt for the appropriate type of rpc
84 * for the frequent rpcs and a default for the others.
85 * The justification for doing "other" this way is that these rpcs
86 * happen so infrequently that timer est. would probably be stale.
87 * Also, since many of these rpcs are
88 * non-idempotent, a conservative timeout is desired.
89 * getattr, lookup,
90 * read, write, commit - A+4D
91 * other - timeo
92 */
93
94unsigned long
95rpc_calc_rto(struct rpc_rtt *rt, unsigned timer)
96{
97 unsigned long res;
98
99 if (timer-- == 0)
100 return rt->timeo;
101
102 res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];
103 if (res > RPC_RTO_MAX)
104 res = RPC_RTO_MAX;
105
106 return res;
107}