Re: [PATCH 13/32] nohz: Adaptive tick stop and restart on nohz cpuset

Peter Zijlstra
2011-08-30T15:29:19Z

On Tue, 2011-08-30 at 16:38 +0200, Frederic Weisbecker wrote:
> On Tue, Aug 30, 2011 at 02:44:10PM +0200, Peter Zijlstra wrote:
> > On Mon, 2011-08-29 at 20:28 +0200, Frederic Weisbecker wrote:
> > > tick_nohz_stop_sched_tick() checks that
> > > with {rcu,printk,arch}_needs_cpu() and restores a periodic behaviour
> > > until nobody else needs the CPU.
> >
> > tick_nohz_stop_sched_tick() should not restore stuff, it should at worst
> > fail to stop but never enable that's just weird.
>
> It's not really enablement, it's just nohz behaviour but the next tick is
> in HZ :o)
>
> Like you said before it's an optimization.

I'm still not feeling very confident about all that..

> I can do the things differently
> for idle and non-idle cases there but I'm not sure it's really a good thing.

its not, but I'm very sure I've lost you on why that should be the case.