ceph/src/common/DecayCounter.h

   1 // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
   2 // vim: ts=8 sw=2 smarttab
   3 /*
   4  * Ceph - scalable distributed file system
   5  *
   6  * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
   7  *
   8  * This is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License version 2.1, as published by the Free Software
  11  * Foundation.  See file COPYING.
  12  *
  13  */
  14
  15 #ifndef CEPH_DECAYCOUNTER_H
  16 #define CEPH_DECAYCOUNTER_H
  17
  18 #include "include/utime.h"
  19
  20 /**
  21  *
  22  * TODO: normalize value based on some fucntion of half_life,
  23  *  so that it can be interpreted as an approximation of a
  24  *  moving average of N seconds.  currently, changing half-life
  25  *  skews the scale of the value, even at steady state.
  26  *
  27  */
  28
  29 class DecayRate {
  30   double k;             // k = ln(.5)/half_life
  31
  32   friend class DecayCounter;
  33
  34 public:
  35   DecayRate() : k(0) {}
  36   DecayRate(const DecayRate &dr) : k(dr.k) {}
  37
  38   // cppcheck-suppress noExplicitConstructor
  39   DecayRate(double hl) { set_halflife(hl); }
  40   void set_halflife(double hl) {
  41     k = ::log(.5) / hl;
  42   }
  43 };
  44
  45 class DecayCounter {
  46 public:
  47   double val;           // value
  48   double delta;         // delta since last decay
  49   double vel;           // recent velocity
  50   utime_t last_decay;   // time of last decay
  51   DecayRate rate;
  52
  53   void encode(bufferlist& bl) const;
  54   void decode(const utime_t &t, bufferlist::iterator& p);
  55   void dump(Formatter *f) const;
  56   static void generate_test_instances(list<DecayCounter*>& ls);
  57
  58   explicit DecayCounter(const utime_t &now)
  59     : val(0), delta(0), vel(0), last_decay(now)
  60   {
  61   }
  62
  63   explicit DecayCounter(const utime_t &now, const DecayRate &rate)
  64     : val(0), delta(0), vel(0), last_decay(now), rate(rate)
  65   {
  66   }
  67
  68   // these two functions are for the use of our dencoder testing infrastructure
  69   DecayCounter() : val(0), delta(0), vel(0), last_decay() {}
  70
  71   void decode(bufferlist::iterator& p) {
  72     utime_t fake_time;
  73     decode(fake_time, p);
  74   }
  75
  76   /**
  77    * reading
  78    */
  79
  80   double get(utime_t now, const DecayRate& rate) {
  81     decay(now, rate);
  82     return val+delta;
  83   }
  84   double get(utime_t now) {
  85     decay(now, rate);
  86     return val+delta;
  87   }
  88
  89   double get_last() const {
  90     return val;
  91   }
  92
  93   double get_last_vel() const {
  94     return vel;
  95   }
  96
  97   utime_t get_last_decay() const {
  98     return last_decay;
  99   }
 100
 101   /**
 102    * adjusting
 103    */
 104
 105   double hit(utime_t now, const DecayRate& rate, double v = 1.0) {
 106     decay(now, rate);
 107     delta += v;
 108     return val+delta;
 109   }
 110   double hit(utime_t now, double v = 1.0) {
 111     decay(now, rate);
 112     delta += v;
 113     return val+delta;
 114   }
 115
 116   void adjust(double a) {
 117     val += a;
 118   }
 119   void adjust(utime_t now, const DecayRate& rate, double a) {
 120     decay(now, rate);
 121     val += a;
 122   }
 123   void scale(double f) {
 124     val *= f;
 125     delta *= f;
 126     vel *= f;
 127   }
 128
 129   /**
 130    * decay etc.
 131    */
 132
 133   void reset(utime_t now) {
 134     last_decay = now;
 135     val = delta = 0;
 136   }
 137
 138   void decay(utime_t now, const DecayRate &rate);
 139 };
 140
 141 inline void encode(const DecayCounter &c, bufferlist &bl) { c.encode(bl); }
 142 inline void decode(DecayCounter &c, const utime_t &t, bufferlist::iterator &p) {
 143   c.decode(t, p);
 144 }
 145 // for dencoder
 146 inline void decode(DecayCounter &c, bufferlist::iterator &p) {
 147   utime_t t;
 148   c.decode(t, p);
 149 }
 150
 151
 152 #endif