linux/net/sunrpc/timer.c
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   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