/*
   * 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);