// SPDX-License-Identifier: GPL-2.0-only
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/*
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* linux/net/sunrpc/timer.c
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*
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* Estimate RPC request round trip time.
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*
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* Based on packet round-trip and variance estimator algorithms described
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* in appendix A of "Congestion Avoidance and Control" by Van Jacobson
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* and Michael J. Karels (ACM Computer Communication Review; Proceedings
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* of the Sigcomm '88 Symposium in Stanford, CA, August, 1988).
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*
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* This RTT estimator is used only for RPC over datagram protocols.
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*
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* Copyright (C) 2002 Trond Myklebust <trond.myklebust@fys.uio.no>
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*/
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#include <asm/param.h>
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#include <linux/types.h>
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#include <linux/unistd.h>
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#include <linux/module.h>
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#include <linux/sunrpc/clnt.h>
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#define RPC_RTO_MAX (60*HZ)
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#define RPC_RTO_INIT (HZ/5)
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#define RPC_RTO_MIN (HZ/10)
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/**
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* rpc_init_rtt - Initialize an RPC RTT estimator context
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* @rt: context to initialize
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* @timeo: initial timeout value, in jiffies
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*
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*/
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void rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo)
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{
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unsigned long init = 0;
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unsigned int i;
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rt->timeo = timeo;
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if (timeo > RPC_RTO_INIT)
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init = (timeo - RPC_RTO_INIT) << 3;
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for (i = 0; i < 5; i++) {
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rt->srtt[i] = init;
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rt->sdrtt[i] = RPC_RTO_INIT;
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rt->ntimeouts[i] = 0;
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}
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}
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EXPORT_SYMBOL_GPL(rpc_init_rtt);
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/**
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* rpc_update_rtt - Update an RPC RTT estimator context
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* @rt: context to update
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* @timer: timer array index (request type)
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* @m: recent actual RTT, in jiffies
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*
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* NB: When computing the smoothed RTT and standard deviation,
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* be careful not to produce negative intermediate results.
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*/
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void rpc_update_rtt(struct rpc_rtt *rt, unsigned int timer, long m)
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{
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long *srtt, *sdrtt;
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if (timer-- == 0)
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return;
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/* jiffies wrapped; ignore this one */
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if (m < 0)
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return;
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if (m == 0)
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m = 1L;
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srtt = (long *)&rt->srtt[timer];
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m -= *srtt >> 3;
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*srtt += m;
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if (m < 0)
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m = -m;
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sdrtt = (long *)&rt->sdrtt[timer];
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m -= *sdrtt >> 2;
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*sdrtt += m;
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/* Set lower bound on the variance */
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if (*sdrtt < RPC_RTO_MIN)
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*sdrtt = RPC_RTO_MIN;
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}
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EXPORT_SYMBOL_GPL(rpc_update_rtt);
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/**
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* rpc_calc_rto - Provide an estimated timeout value
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* @rt: context to use for calculation
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* @timer: timer array index (request type)
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*
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* Estimate RTO for an NFS RPC sent via an unreliable datagram. Use
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* the mean and mean deviation of RTT for the appropriate type of RPC
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* for frequently issued RPCs, and a fixed default for the others.
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*
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* The justification for doing "other" this way is that these RPCs
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* happen so infrequently that timer estimation would probably be
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* stale. Also, since many of these RPCs are non-idempotent, a
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* conservative timeout is desired.
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*
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* getattr, lookup,
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* read, write, commit - A+4D
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* other - timeo
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*/
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unsigned long rpc_calc_rto(struct rpc_rtt *rt, unsigned int timer)
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{
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unsigned long res;
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if (timer-- == 0)
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return rt->timeo;
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res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];
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if (res > RPC_RTO_MAX)
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res = RPC_RTO_MAX;
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return res;
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}
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EXPORT_SYMBOL_GPL(rpc_calc_rto);
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