linux-kernel - Re: [Query]: tick-sched: why don't we stop tick when we are running idle task?

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Date:	Mon, 14 Apr 2014 14:06:00 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: [Query]: tick-sched: why don't we stop tick when we are running
 idle task?

On Mon, Apr 14, 2014 at 05:22:30PM +0530, Viresh Kumar wrote:
> On 14 April 2014 17:17, Peter Zijlstra <peterz@...radead.org> wrote:
> > What causes this tick? I was under the impression that once there's a
> > single task (not doing any syscalls) and the above issues are sorted, no
> > more tick would happen.
> 
> This is what Frederic told me earlier:
> 
> https://lkml.org/lkml/2014/2/13/238

That's a bit of a non-answer. I'm fairly sure its not a gazillion
issues, since the actual scheduler tick doesn't actually do that much.

So start by enumerating what is actually required.

The 2), which I suppose you're now trying to implement is I think
entirely the wrong way. The tick really assumes it runs local, moving it
to another CPU is insane.
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