linux-kernel - Re: [PATCH 07/10] sched: Migrate sched to use new tick dependency mask model

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Date:	Mon, 10 Aug 2015 15:02:04 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Ingo Molnar <mingo@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 07/10] sched: Migrate sched to use new tick dependency
 mask model

Hi,

On 04/08/15 08:41, Peter Zijlstra wrote:
> On Mon, Aug 03, 2015 at 07:30:32PM +0200, Frederic Weisbecker wrote:
>>> But you've forgotten about SCHED_DEADLINE, we count those in:
>>> rq->dl.dl_nr_running.
>>
>> Indeed. Hmm, there is no preemption between SCHED_DEALINE tasks, right?
>> So I can treat it like SCHED_FIFO.
> 
> Sadly no. Even though EDF has static job priority (once a job is
> activated its priority doesn't change anymore) DEADLINE also has a CBS
> component and that needs the tick regardless, even with a single task.
> 
> So any deadline task running means we cannot stop the tick.

Well, couldn't we stop it when we use hrtick? As start_hrtick_dl() sets
the hrtick to fire at tasks runtime depletion instant.

Thanks,

- Juri

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