[tip:perf/core] perf stats: Fix divide by 0 in variance

[tip-bot for David Ahern]

Commit-ID:  45528f7c699a71d2f3096173980aadd43dff6eaa
Gitweb:     http://git.kernel.org/tip/45528f7c699a71d2f3096173980aadd43dff6eaa
Author:     David Ahern <dsahern@xxxxxxxxx>
AuthorDate: Sat, 25 May 2013 18:24:48 -0600
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Tue, 28 May 2013 16:24:04 +0300

perf stats: Fix divide by 0 in variance

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@xxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Runzhen Wang <runzhen@xxxxxxxxxxxxxxxxxx>
Cc: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1369527896-3650-9-git-send-email-dsahern@xxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/stat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/stat.c b/tools/perf/util/stat.c
index 2374212..7c59c28 100644
--- a/tools/perf/util/stat.c
+++ b/tools/perf/util/stat.c
@@ -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);
--
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