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

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Date:	Tue, 4 Aug 2015 09:41:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	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

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.
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