cpuidle: Add a comment warning about possible overflow

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 <[email protected]> Signed-off-by: Rafael J. Wysocki <[email protected]>
oohal · Aug 22, 2013 · decd51b · decd51b
1 parent 0e96d5a
commit decd51b
Showing 1 changed file with 9 additions and 0 deletions.
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
@@ -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