* [PATCH] cpuidle: menu: Avoid overflows when computing variance
@ 2019-02-27 13:35 Rafael J. Wysocki
0 siblings, 0 replies; only message in thread
From: Rafael J. Wysocki @ 2019-02-27 13:35 UTC (permalink / raw)
To: Linux PM; +Cc: LKML, Peter Zijlstra, Randy Dunlap
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(-)
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:
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2019-02-27 13:35 [PATCH] cpuidle: menu: Avoid overflows when computing variance Rafael J. Wysocki
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