1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * linux/net/sunrpc/timer.c
4 *
5 * Estimate RPC request round trip time.
6 *
7 * Based on packet round-trip and variance estimator algorithms described
8 * in appendix A of "Congestion Avoidance and Control" by Van Jacobson
9 * and Michael J. Karels (ACM Computer Communication Review; Proceedings
10 * of the Sigcomm '88 Symposium in Stanford, CA, August, 1988).
11 *
12 * This RTT estimator is used only for RPC over datagram protocols.
13 *
14 * Copyright (C) 2002 Trond Myklebust <trond.myklebust@fys.uio.no>
15 */
16
17#include <asm/param.h>
18
19#include <linux/types.h>
20#include <linux/unistd.h>
21#include <linux/module.h>
22
23#include <linux/sunrpc/clnt.h>
24
25#define RPC_RTO_MAX (60*HZ)
26#define RPC_RTO_INIT (HZ/5)
27#define RPC_RTO_MIN (HZ/10)
28
29/**
30 * rpc_init_rtt - Initialize an RPC RTT estimator context
31 * @rt: context to initialize
32 * @timeo: initial timeout value, in jiffies
33 *
34 */
35void rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo)
36{
37 unsigned long init = 0;
38 unsigned int i;
39
40 rt->timeo = timeo;
41
42 if (timeo > RPC_RTO_INIT)
43 init = (timeo - RPC_RTO_INIT) << 3;
44 for (i = 0; i < 5; i++) {
45 rt->srtt[i] = init;
46 rt->sdrtt[i] = RPC_RTO_INIT;
47 rt->ntimeouts[i] = 0;
48 }
49}
50EXPORT_SYMBOL_GPL(rpc_init_rtt);
51
52/**
53 * rpc_update_rtt - Update an RPC RTT estimator context
54 * @rt: context to update
55 * @timer: timer array index (request type)
56 * @m: recent actual RTT, in jiffies
57 *
58 * NB: When computing the smoothed RTT and standard deviation,
59 * be careful not to produce negative intermediate results.
60 */
61void rpc_update_rtt(struct rpc_rtt *rt, unsigned int timer, long m)
62{
63 long *srtt, *sdrtt;
64
65 if (timer-- == 0)
66 return;
67
68 /* jiffies wrapped; ignore this one */
69 if (m < 0)
70 return;
71
72 if (m == 0)
73 m = 1L;
74
75 srtt = (long *)&rt->srtt[timer];
76 m -= *srtt >> 3;
77 *srtt += m;
78
79 if (m < 0)
80 m = -m;
81
82 sdrtt = (long *)&rt->sdrtt[timer];
83 m -= *sdrtt >> 2;
84 *sdrtt += m;
85
86 /* Set lower bound on the variance */
87 if (*sdrtt < RPC_RTO_MIN)
88 *sdrtt = RPC_RTO_MIN;
89}
90EXPORT_SYMBOL_GPL(rpc_update_rtt);
91
92/**
93 * rpc_calc_rto - Provide an estimated timeout value
94 * @rt: context to use for calculation
95 * @timer: timer array index (request type)
96 *
97 * Estimate RTO for an NFS RPC sent via an unreliable datagram. Use
98 * the mean and mean deviation of RTT for the appropriate type of RPC
99 * for frequently issued RPCs, and a fixed default for the others.
100 *
101 * The justification for doing "other" this way is that these RPCs
102 * happen so infrequently that timer estimation would probably be
103 * stale. Also, since many of these RPCs are non-idempotent, a
104 * conservative timeout is desired.
105 *
106 * getattr, lookup,
107 * read, write, commit - A+4D
108 * other - timeo
109 */
110unsigned long rpc_calc_rto(struct rpc_rtt *rt, unsigned int timer)
111{
112 unsigned long res;
113
114 if (timer-- == 0)
115 return rt->timeo;
116
117 res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];
118 if (res > RPC_RTO_MAX)
119 res = RPC_RTO_MAX;
120
121 return res;
122}
123EXPORT_SYMBOL_GPL(rpc_calc_rto);
124