linux-kernel - Re: [question] sched: idle

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Message-ID: <52A7BF24.1080101@linaro.org>
Date:	Wed, 11 Dec 2013 09:25:56 +0800
From:	Alex Shi <alex.shi@...aro.org>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mike Galbraith <bitbucket@...ine.de>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [question] sched: idle_avg and migration latency

On 12/11/2013 02:31 AM, Daniel Lezcano wrote:
>>
>> That has changed a little recently.  I originally slammed avg_idle
>> itself straight to max to ensure that a bursty load would idle balance,
>> and not use stale data.  If you start cross core switching at high
>> frequency, you'll still shut idle balancing quickly.
> 
> Ok, thanks for the explanation.
> 
> I think I am a bit puzzled with the 'idle_avg' name. I am guessing the
> semantic of this variable is "how long this cpu has been idle".
> 
> The idle duration, with the no_hz, could be long, several seconds if the
> work queues have been migrated and if the timer affinity is set to
> another cpu. So if we fall in this case and there is a burst of activity
> + micro-idle and idle_avg is not leverage to max, it will stay high
> during an amount of time, thus pulling tasks at each micro idle period,
> right ?

yes, I think so.

-- 
Thanks
    Alex
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