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

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Message-ID: <20140513233036.GH13828@localhost.localdomain>
Date:	Wed, 14 May 2014 01:30:39 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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 Fri, May 09, 2014 at 02:14:10PM +0530, Viresh Kumar wrote:
> On 23 April 2014 16:42, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > On 15 April 2014 15:00, Frederic Weisbecker <fweisbec@...il.com> wrote:
> >> Ok, I'm a bit buzy with a conference right now but I'm going to summarize that
> >> soonish.
> 
> Hi Frederic,
> 
> Please see if you can find some time to close this, that would be very
> helpful :)
> 
> Thanks

I'm generally worried about the accounting in update_curr() that periodically
updates stats. I have no idea which of these stats could be read by other CPUs:
vruntime, load bandwitdth, etc...

Also without tick:

* we don't poll anymore on trigger_load_balance()

* __update_cpu_load() requires fixed rate periodic polling. Alex Shi had
patches for that but I'm not sure if that's going to be merged

* rq->rt_avg accounting?
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