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  • ipipe-x86
  • kernel
  • trace
  • ftrace.c
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  • Juri Lelli's avatar
    ftrace: Fix stddev calculation in function profiler · 52d85d76
    Juri Lelli authored Jun 12, 2013
    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: default avatarJuri Lelli <juri.lelli@gmail.com>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    52d85d76

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