From: Jens Axboe <jens.axboe@oracle.com>
Date: Wed, 10 Jan 2007 14:39:51 +0000 (+0100)
Subject: [PATCH] Fix standard deviation calculation
X-Git-Tag: fio-1.12~171
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=ddf4a69b083416fa0e626f591b3b425085656531;p=fio.git

[PATCH] Fix standard deviation calculation

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---

diff --git a/stat.c b/stat.c
index a84f28a5..6e7c2357 100644
--- a/stat.c
+++ b/stat.c
@@ -298,11 +298,11 @@ static int calc_lat(struct io_stat *is, unsigned long *min, unsigned long *max,
 	if (n <= 1.0)
 		return 1;
 
-	o = (double) is->val_sq - ((*mean * *mean) / n);
+	o = ((double) is->val_sq - (*mean * is->val)) / n;
 	if (o < 0.0)
 		*dev = -1.0;
 	else
-		*dev = sqrt(o / (n - 1.0));
+		*dev = sqrt(o);
 
 	return 1;
 }