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

From: Peter Zijlstra <peterz@infradead.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Lists linaro-kernel <linaro-kernel@lists.linaro.org>
Subject: Re: [Query]: tick-sched: why don't we stop tick when we are running idle task?
Date: Mon, 14 Apr 2014 13:02:45 +0200	[thread overview]
Message-ID: <20140414110245.GG11096@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CAKohpomgv-LbUcPxazfJkf0Jq0sSULxT0WjrbFovn0k0O-ORwg@mail.gmail.com>

On Fri, Apr 11, 2014 at 10:08:30PM +0530, Viresh Kumar wrote:
> On 11 April 2014 20:48, Peter Zijlstra <peterz@infradead.org> wrote:
> > On Fri, Apr 11, 2014 at 04:53:35PM +0200, Frederic Weisbecker wrote:
> 
> > I think there's assumptions that tick runs on the local cpu;
> 
> Yes, many function behave that way, i.e. with smp_processor_id() as
> CPU.
> 
> > also what
> > are you going to do when running it on all remote cpus takes longer than
> > the tick?
> >
> >> Otherwise (and ideally) we need to make the scheduler code able to handle long periods without
> >> calling scheduler_tick(). But this is a lot more plumbing. And the scheduler has gazillions
> >> accounting stuffs to handle. Sounds like a big nightmare to take that direction.
> >
> > So i'm not at all sure what you guys are talking about, but it seems to
> > me you should all put down the bong and have a detox round instead.
> >
> > This all sounds like a cure worse than the problem.
> 
> So, what I was working on isn't ready yet but I would like to show what lines
> I have been trying on. In case that is completely incorrect and I should stop
> making that work :)
> 
> Please share your feedback about this (Yes there are several parts broken
> currently, specially the assumption that tick runs on local CPU):

I'm still not sure _what_ you're trying to solve here. What are you
doing and why?