linux-kernel - Re: [RFC PATCH v3 3/6] sched: pack small tasks

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Message-ID: <CAKfTPtBU40WZU8n-vS=APG4oirBuVR4LB8VNRQ6OT2pr1PhcKQ@mail.gmail.com>
Date:	Tue, 26 Mar 2013 14:00:50 +0100
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, mingo@...nel.org,
	linux@....linux.org.uk, pjt@...gle.com, santosh.shilimkar@...com,
	morten.rasmussen@....com, chander.kashyap@...aro.org,
	cmetcalf@...era.com, tony.luck@...el.com, alex.shi@...el.com,
	preeti@...ux.vnet.ibm.com, paulmck@...ux.vnet.ibm.com,
	tglx@...utronix.de, len.brown@...el.com, arjan@...ux.intel.com,
	amit.kucheria@...aro.org, corbet@....net
Subject: Re: [RFC PATCH v3 3/6] sched: pack small tasks

On 26 March 2013 13:37, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, 2013-03-22 at 13:25 +0100, Vincent Guittot wrote:
>> +static bool is_light_task(struct task_struct *p)
>> +{
>> +       /* A light task runs less than 20% in average */
>> +       return ((p->se.avg.runnable_avg_sum  * 5) <
>> +                       (p->se.avg.runnable_avg_period));
>> +}
>
> OK, so we have a 'problem' here, we initialize runnable_avg_* to 0, but
> we want to 'assume' a fresh task is fully 'loaded'. IIRC Alex ran into
> this as well.
Hi Peter,

The packing small tasks is only applied at wake up and not during fork
or exec so the runnable_avg_* should have been initialized. As you
mentionned, we assume that a fresh task is fully loaded and let the
default scheduler behavior to select a target CPU

Vincent

>
> PJT, do you have any sane solution for this, I forgot what the result
> of the last discussion was -- was there any?
>
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