linux-kernel - Re: [PATCH 2/2] cpuidle: Add a repeating pattern detector to the menu governor

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Message-ID: <20100522093156.406eacd5@infradead.org>
Date:	Sat, 22 May 2010 09:31:56 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	frank.rowand@...sony.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] cpuidle: Add a repeating pattern detector to the
 menu governor

On Fri, 21 May 2010 12:43:09 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:
> > Should the following division by INTERVALS be moved up 6 lines to
> > before "if (avg > data->expected_us)"?
> 
> Quite possibly.

>From 7350a9007eee802eaa9e4c1878dd5a2ea4d6f7f9 Mon Sep 17 00:00:00 2001
From: Arjan van de Ven <arjan@...ux.intel.com>
Date: Sat, 22 May 2010 09:29:29 -0700
Subject: [PATCH] cpuidle: fix bug in the pattern detector as reported by Frank Rowand

Frank Rowand found a bug in the new pattern detector code where
the average value was looked at before the sum of values got divided
by the number of samples.

Signed-off-by: Arjan van de Ven <arjan@...ux.intel.com>
CC: akpm@...ux-foundation.org
CC: frank.rowand@...sony.com
---
 drivers/cpuidle/governors/menu.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index f3d4783..52ff8aa 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -205,12 +205,12 @@ static void detect_repeating_patterns(struct menu_device *data)
 	/* first calculate average and standard deviation of the past */
 	for (i = 0; i < INTERVALS; i++)
 		avg += data->intervals[i];
+	avg = avg / INTERVALS;
 
 	/* if the avg is beyond the known next tick, it's worthless */
 	if (avg > data->expected_us)
 		return;
 
-	avg = avg / INTERVALS;
 	for (i = 0; i < INTERVALS; i++)
 		stddev += (data->intervals[i] - avg) *
 			  (data->intervals[i] - avg);
-- 
1.6.2.5

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