From: Juri Lelli <juri.lelli@gmail.com>
Date: Wed, 12 Jun 2013 10:03:18 +0000 (+0200)
Subject: ftrace: Fix stddev calculation in function profiler
X-Git-Tag: v3.11-rc1~33^2~22
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=52d85d763086594f139bf7d3a5641abeb91d9f57;p=pandora-kernel.git

ftrace: Fix stddev calculation in function profiler

When FUNCTION_GRAPH_TRACER is enabled, ftrace can profile kernel functions
and print basic statistics about them. Unfortunately, running stddev
calculation is wrong. This patch corrects it implementing Welford’s method:

        s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2) .
Link: http://lkml.kernel.org/r/1371031398-24048-1-git-send-email-juri.lelli@gmail.com

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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