LXR linux/net/sunrpc/timer.c

   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