/* * 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 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 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 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);