perf stat: Use stddev_mean in stead of stddev

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When we're computing the mean by sampling the distribution,
then the std dev of the mean is related to the std dev of the
sample set by:

  stddev_mean = std_dev / sqrt(N)

Which is exactly what we want.

This results in the error on the mean decreasing with
increasing number of samples.

Also fix the scaled == -1, aka not counted case.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

...

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Peter Zijlstra 2009-09-04 17:03:13 +02:00 • committed by Ingo Molnar

parent 9e9772c458

commit 63d40deb2e

1 changed files with 19 additions and 6 deletions

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tools/perf/builtin-stat.c

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