Date: Tue, 4 Aug 2015 09:41:16 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>,
        Christoph Lameter <cl@linux.com>, Ingo Molnar <mingo@kernel.org>,
        Viresh Kumar <viresh.kumar@linaro.org>, Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH 07/10] sched: Migrate sched to use new tick dependency
 mask model
Message-ID: <20150804074116.GH25159@twins.programming.kicks-ass.net>
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 <20150803145031.GD25554@lerouge>
 <20150803170911.GV25159@twins.programming.kicks-ass.net>
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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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