timer.c

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/*
 * linux/net/sunrpc/timer.c
 *
 * Estimate RPC request round trip time.
 *
 * Based on packet round-trip and variance estimator algorithms described
 * in appendix A of "Congestion Avoidance and Control" by Van Jacobson
 * and Michael J. Karels (ACM Computer Communication Review; Proceedings
 * of the Sigcomm '88 Symposium in Stanford, CA, August, 1988).
 *
 * This RTT estimator is used only for RPC over datagram protocols.
 *
 * Copyright (C) 2002 Trond Myklebust <[email protected]>
 */

#include <asm/param.h>

#include <linux/types.h>
#include <linux/unistd.h>
#include <linux/module.h>

#include <linux/sunrpc/clnt.h>

#define RPC_RTO_MAX (60*HZ)
#define RPC_RTO_INIT (HZ/5)
#define RPC_RTO_MIN (HZ/10)

void rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo)
{
    unsigned long init = 0;
    unsigned int i;

    rt->timeo = timeo;

    if (timeo > RPC_RTO_INIT)
        init = (timeo - RPC_RTO_INIT) << 3;
    for (i = 0; i < 5; i++) {
        rt->srtt[i] = init;
        rt->sdrtt[i] = RPC_RTO_INIT;
        rt->ntimeouts[i] = 0;
    }
}
EXPORT_SYMBOL_GPL(rpc_init_rtt);

void rpc_update_rtt(struct rpc_rtt *rt, unsigned int timer, long m)
{
    long *srtt, *sdrtt;

    if (timer-- == 0)
        return;

    /* jiffies wrapped; ignore this one */
    if (m < 0)
        return;

    if (m == 0)
        m = 1L;

    srtt = (long *)&rt->srtt[timer];
    m -= *srtt >> 3;
    *srtt += m;

    if (m < 0)
        m = -m;

    sdrtt = (long *)&rt->sdrtt[timer];
    m -= *sdrtt >> 2;
    *sdrtt += m;

    /* Set lower bound on the variance */
    if (*sdrtt < RPC_RTO_MIN)
        *sdrtt = RPC_RTO_MIN;
}
EXPORT_SYMBOL_GPL(rpc_update_rtt);

unsigned long rpc_calc_rto(struct rpc_rtt *rt, unsigned int timer)
{
    unsigned long res;

    if (timer-- == 0)
        return rt->timeo;

    res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];
    if (res > RPC_RTO_MAX)
        res = RPC_RTO_MAX;

    return res;
}
EXPORT_SYMBOL_GPL(rpc_calc_rto);