[RFC PATCH 1/2] sched/update_avg: avoid negative time

[Alex Shi]

rq->avg_idle try to reflect the average idle time between the cpu idle
and first wakeup. But in the function, it maybe get a negative value
if old avg_idle is too small. Then this negative value will be double
counted in next time calculation. Guess that is not the original purpose,
so recalibrate it to zero.

Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxx>
---
 kernel/sched/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 30eb011..af9121c6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1358,6 +1358,9 @@ static void update_avg(u64 *avg, u64 sample)
 {
 	s64 diff = sample - *avg;
 	*avg += diff >> 3;
+
+	if (*avg < 0)
+		*avg = 0;
 }
 #endif
 
-- 
1.8.1.2

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