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cpuidle: menu: Avoid overflows when computing variance

Message ID 13496310.XaNEd20TYL@aspire.rjw.lan (mailing list archive)
State Accepted, archived
Delegated to: Rafael Wysocki
Headers show
Series cpuidle: menu: Avoid overflows when computing variance | expand

Commit Message

Rafael J. Wysocki Feb. 27, 2019, 1:35 p.m. UTC 
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

The variance computation in get_typical_interval() may overflow if
the square of the value of diff exceeds the maximum for the int64_t
data type value which basically is the case when it is of the order
of UINT_MAX.

However, data points so far in the future don't matter for idle
state selection anyway, so change the initial threshold value in
get_typical_interval() to INT_MAX which will cause more "outlying"
data points to be discarded without affecting the selection result.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/cpuidle/governors/menu.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff mbox series

Patch

Index: linux-pm/drivers/cpuidle/governors/menu.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/governors/menu.c
+++ linux-pm/drivers/cpuidle/governors/menu.c
@@ -186,7 +186,7 @@  static unsigned int get_typical_interval
 	unsigned int min, max, thresh, avg;
 	uint64_t sum, variance;
 
-	thresh = UINT_MAX; /* Discard outliers above this value */
+	thresh = INT_MAX; /* Discard outliers above this value */
 
 again: