tools/perf/util/stat.c

   1 #include <math.h>
   2
   3 #include "stat.h"
   4
   5 void update_stats(struct stats *stats, u64 val)
   6 {
   7         double delta;
   8
   9         stats->n++;
  10         delta = val - stats->mean;
  11         stats->mean += delta / stats->n;
  12         stats->M2 += delta*(val - stats->mean);
  13
  14         if (val > stats->max)
  15                 stats->max = val;
  16
  17         if (val < stats->min)
  18                 stats->min = val;
  19 }
  20
  21 double avg_stats(struct stats *stats)
  22 {
  23         return stats->mean;
  24 }
  25
  26 /*
  27  * http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance
  28  *
  29  *       (\Sum n_i^2) - ((\Sum n_i)^2)/n
  30  * s^2 = -------------------------------
  31  *                  n - 1
  32  *
  33  * http://en.wikipedia.org/wiki/Stddev
  34  *
  35  * The std dev of the mean is related to the std dev by:
  36  *
  37  *             s
  38  * s_mean = -------
  39  *          sqrt(n)
  40  *
  41  */
  42 double stddev_stats(struct stats *stats)
  43 {
  44         double variance, variance_mean;
  45
  46         if (stats->n < 2)
  47                 return 0.0;
  48
  49         variance = stats->M2 / (stats->n - 1);
  50         variance_mean = variance / stats->n;
  51
  52         return sqrt(variance_mean);
  53 }
  54
  55 double rel_stddev_stats(double stddev, double avg)
  56 {
  57         double pct = 0.0;
  58
  59         if (avg)
  60                 pct = 100.0 * stddev/avg;
  61
  62         return pct;
  63 }