Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 8a02631a authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

perf stat: More advanced variance computation 



Use the more advanced single pass variance algorithm outlined
on the wikipedia page. This is numerically more stable for
larger sample sets.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 63d40deb

tools/perf/builtin-stat.c

+12 −12
Original line number Diff line number Diff line
@@ -79,28 +79,29 @@ static int event_scaled[MAX_COUNTERS]; 


struct stats

{

	double sum;

	double sum_sq;

	double n, mean, M2;

};



static void update_stats(struct stats *stats, u64 val)

{

	double sq = val;

	double delta;



	stats->sum += val;

	stats->sum_sq += sq * sq;

	stats->n++;

	delta = val - stats->mean;

	stats->mean += delta / stats->n;

	stats->M2 += delta*(val - stats->mean);

}



static double avg_stats(struct stats *stats)

{

	return stats->sum / run_count;

	return stats->mean;

}



/*

 * http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance

 *

 *       (\Sum n_i^2) - ((\Sum n_i)^2)/n

 * s^2  -------------------------------

 * s^2 = -------------------------------

 *                  n - 1

 *

 * http://en.wikipedia.org/wiki/Stddev
@@ -114,9 +115,8 @@ static double avg_stats(struct stats *stats) 
 */

static double stddev_stats(struct stats *stats)

{

	double avg = stats->sum / run_count;

	double variance = (stats->sum_sq - stats->sum*avg)/(run_count - 1);

	double variance_mean = variance / run_count;

	double variance = stats->M2 / (stats->n - 1);

	double variance_mean = variance / stats->n;



	return sqrt(variance_mean);

}