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// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
// vim: ts=8 sw=2 smarttab
/*
* Ceph - scalable distributed file system
*
* Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
*
* This is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License version 2.1, as published by the Free Software
* Foundation. See file COPYING.
*
*/
#ifndef CEPH_DECAYCOUNTER_H
#define CEPH_DECAYCOUNTER_H
#include "include/utime.h"
#include <math.h>
/**
*
* TODO: normalize value based on some fucntion of half_life,
* so that it can be interpreted as an approximation of a
* moving average of N seconds. currently, changing half-life
* skews the scale of the value, even at steady state.
*
*/
class DecayRate {
double k; // k = ln(.5)/half_life
friend class DecayCounter;
public:
DecayRate() : k(0) {}
DecayRate(double hl) { set_halflife(hl); }
void set_halflife(double hl) {
k = ::log(.5) / hl;
}
};
class DecayCounter {
protected:
public:
double val; // value
double delta; // delta since last decay
double vel; // recent velocity
utime_t last_decay; // time of last decay
public:
void encode(bufferlist& bl) const {
__u8 struct_v = 3;
::encode(struct_v, bl);
::encode(val, bl);
::encode(delta, bl);
::encode(vel, bl);
}
void decode(const utime_t &t, bufferlist::iterator &p) {
__u8 struct_v;
::decode(struct_v, p);
if (struct_v < 2) {
double half_life;
::decode(half_life, p);
}
if (struct_v < 3) {
double k;
::decode(k, p);
}
::decode(val, p);
::decode(delta, p);
::decode(vel, p);
}
DecayCounter(const utime_t &now)
: val(0), delta(0), vel(0), last_decay(now)
{
}
/**
* reading
*/
double get(utime_t now, const DecayRate& rate) {
decay(now, rate);
return val;
}
double get_last() {
return val;
}
double get_last_vel() {
return vel;
}
utime_t get_last_decay() {
return last_decay;
}
/**
* adjusting
*/
double hit(utime_t now, const DecayRate& rate, double v = 1.0) {
decay(now, rate);
delta += v;
return val+delta;
}
void adjust(double a) {
val += a;
}
void adjust(utime_t now, const DecayRate& rate, double a) {
decay(now, rate);
val += a;
}
void scale(double f) {
val *= f;
delta *= f;
vel *= f;
}
/**
* decay etc.
*/
void reset(utime_t now) {
last_decay = now;
val = delta = 0;
}
void decay(utime_t now, const DecayRate &rate) {
utime_t el = now;
el -= last_decay;
if (el.sec() >= 1) {
// calculate new value
double newval = (val+delta) * exp((double)el * rate.k);
if (newval < .01) newval = 0.0;
// calculate velocity approx
vel += (newval - val) * (double)el;
vel *= exp((double)el * rate.k);
val = newval;
delta = 0;
last_decay = now;
}
}
};
inline void encode(const DecayCounter &c, bufferlist &bl) { c.encode(bl); }
inline void decode(DecayCounter &c, const utime_t &t, bufferlist::iterator &p) {
c.decode(t, p);
}
#endif
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