linux-kernel - [PATCH 08/16] perf stats: fix divide by 0 in variance

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Date:	Sat, 25 May 2013 18:24:48 -0600
From:	David Ahern <dsahern@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	acme@...stprotocols.net, mingo@...nel.org, fweisbec@...il.com,
	peterz@...radead.org, jolsa@...hat.com, namhyung@...nel.org,
	xiaoguangrong@...ux.vnet.ibm.com, runzhen@...ux.vnet.ibm.com,
	David Ahern <dsahern@...il.com>
Subject: [PATCH 08/16] 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@...il.com>
Cc: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc: Runzhen Wang <runzhen@...ux.vnet.ibm.com>
---
 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);
-- 
1.7.10.1

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