root/net/sunrpc/timer.c

DEFINITIONS

1. rpc_init_rtt
2. rpc_update_rtt
3. rpc_calc_rto

/*
 * 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 <trond.myklebust@fys.uio.no>
 */

#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 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);

/*
 * NB: When computing the smoothed RTT and standard deviation,
 *     be careful not to produce negative intermediate results.
 */
void
rpc_update_rtt(struct rpc_rtt *rt, unsigned 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);

/*
 * Estimate rto for an nfs rpc sent via. an unreliable datagram.
 * Use the mean and mean deviation of rtt for the appropriate type of rpc
 * for the frequent rpcs and a default for the others.
 * The justification for doing "other" this way is that these rpcs
 * happen so infrequently that timer est. would probably be stale.
 * Also, since many of these rpcs are
 * non-idempotent, a conservative timeout is desired.
 * getattr, lookup,
 * read, write, commit     - A+4D
 * other                   - timeo
 */

unsigned long
rpc_calc_rto(struct rpc_rtt *rt, unsigned 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);