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cpuidle: Add a comment warning about possible overflow

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The menu governor has a number of tunable constants that may be changed
in the source. If certain combination of values are chosen, an overflow
is possible when the correction_factor is being recalculated.

This patch adds a warning regarding this possibility and describes the
change needed for fixing the issue. The change should not be permanently
enabled, as it will hurt performance when it is not needed.

Signed-off-by: Tuukka Tikkanen <tuukka.tikkanen@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Tuukka Tikkanen 2013-08-14 19:02:40 +03:00 committed by Rafael J. Wysocki
parent 0e96d5adcf
commit decd51bbcd
1 changed files with 9 additions and 0 deletions
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9
drivers/cpuidle/governors/menu.c
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@ -21,6 +21,15 @@
#include <linux/math64.h>
#include <linux/module.h>
/*
* Please note when changing the tuning values:
* If (MAX_INTERESTING-1) * RESOLUTION > UINT_MAX, the result of
* a scaling operation multiplication may overflow on 32 bit platforms.
* In that case, #define RESOLUTION as ULL to get 64 bit result:
* #define RESOLUTION 1024ULL
*
* The default values do not overflow.
*/
#define BUCKETS 12
#define INTERVALS 8
#define RESOLUTION 1024