linux-kernel - [PATCH 1/4] cpuidle: menu: Use shifts when calculating averages where possible

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Message-Id: <1407331161-4642-2-git-send-email-mgorman@suse.de>
Date:	Wed,  6 Aug 2014 14:19:18 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Rafael J Wysocki <rafael.j.wysocki@...el.com>,
	Nicolas Pitre <nico@...aro.org>
Cc:	Mike Galbraith <mgalbraith@...e.de>,
	LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...e.de>
Subject: [PATCH 1/4] cpuidle: menu: Use shifts when calculating averages where possible

We use do_div even though the divisor will usually be a power-of-two
unless there are unusual outliers. Use shifts where possible

Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 drivers/cpuidle/governors/menu.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index c4f80c1..801b2ee 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -31,7 +31,8 @@
  * The default values do not overflow.
  */
 #define BUCKETS 12
-#define INTERVALS 8
+#define INTERVAL_SHIFT 3
+#define INTERVALS (1UL << INTERVAL_SHIFT)
 #define RESOLUTION 1024
 #define DECAY 8
 #define MAX_INTERESTING 50000
@@ -228,7 +229,10 @@ again:
 				max = value;
 		}
 	}
-	do_div(avg, divisor);
+	if (divisor == INTERVALS)
+		avg >>= INTERVAL_SHIFT;
+	else
+		do_div(avg, divisor);
 
 	/* Then try to determine standard deviation */
 	stddev = 0;
@@ -239,7 +243,11 @@ again:
 			stddev += diff * diff;
 		}
 	}
-	do_div(stddev, divisor);
+	if (divisor == INTERVALS)
+		stddev >>= INTERVAL_SHIFT;
+	else
+		do_div(stddev, divisor);
+
 	/*
 	 * The typical interval is obtained when standard deviation is small
 	 * or standard deviation is small compared to the average interval.
-- 
1.8.4.5

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