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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 <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)
/**
* rpc_init_rtt - Initialize an RPC RTT estimator context
* @rt: context to initialize
* @timeo: initial timeout value, in jiffies
*
*/
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);
/**
* rpc_update_rtt - Update an RPC RTT estimator context
* @rt: context to update
* @timer: timer array index (request type)
* @m: recent actual RTT, in jiffies
*
* 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 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);
/**
* rpc_calc_rto - Provide an estimated timeout value
* @rt: context to use for calculation
* @timer: timer array index (request type)
*
* 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 frequently issued RPCs, and a fixed default for the others.
*
* The justification for doing "other" this way is that these RPCs
* happen so infrequently that timer estimation 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 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);
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