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perf stats: Fix divide by 0 in variance

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Number of samples needs to be greater 1 to have a variance.

Fixes nan% in perf-kvm-live output.

Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Runzhen Wang <runzhen@linux.vnet.ibm.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1369527896-3650-9-git-send-email-dsahern@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
David Ahern 2013-05-25 18:24:48 -06:00 committed by Arnaldo Carvalho de Melo
parent 6ca5f3081f
commit 45528f7c69
1 changed files with 1 additions and 1 deletions
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2
tools/perf/util/stat.c
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@ -37,7 +37,7 @@ double stddev_stats(struct stats *stats)
{
double variance, variance_mean;
if (!stats->n)
if (stats->n < 2)
return 0.0;
variance = stats->M2 / (stats->n - 1);