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Message-Id: <1390282399-17091-1-git-send-email-alex.shi@linaro.org>
Date:	Tue, 21 Jan 2014 13:33:18 +0800
From:	Alex Shi <alex.shi@...aro.org>
To:	mingo@...hat.com, peterz@...radead.org, morten.rasmussen@....com,
	vincent.guittot@...aro.org, daniel.lezcano@...aro.org,
	efault@....de
Cc:	wangyun@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	Alex Shi <alex.shi@...aro.org>
Subject: [RFC PATCH 1/2] sched/update_avg: avoid negative time

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@...aro.org>
---
 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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