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
  15 double avg_stats(struct stats *stats)
  16 {
  17         return stats->mean;
  18 }
  19
  20 /*
  21  * http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance
  22  *
  23  *       (\Sum n_i^2) - ((\Sum n_i)^2)/n
  24  * s^2 = -------------------------------
  25  *                  n - 1
  26  *
  27  * http://en.wikipedia.org/wiki/Stddev
  28  *
  29  * The std dev of the mean is related to the std dev by:
  30  *
  31  *             s
  32  * s_mean = -------
  33  *          sqrt(n)
  34  *
  35  */
  36 double stddev_stats(struct stats *stats)
  37 {
  38         double variance, variance_mean;
  39
  40         if (!stats->n)
  41                 return 0.0;
  42
  43         variance = stats->M2 / (stats->n - 1);
  44         variance_mean = variance / stats->n;
  45
  46         return sqrt(variance_mean);
  47 }
  48
  49 double rel_stddev_stats(double stddev, double avg)
  50 {
  51         double pct = 0.0;
  52
  53         if (avg)
  54                 pct = 100.0 * stddev/avg;
  55
  56         return pct;
  57 }