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

Peter Zijlstra
2011-08-29T18:07:30Z

On Mon, 2011-08-29 at 20:02 +0200, Frederic Weisbecker wrote:
> On Mon, Aug 29, 2011 at 05:28:09PM +0200, Peter Zijlstra wrote:
> > On Mon, 2011-08-15 at 17:52 +0200, Frederic Weisbecker wrote:
> > > +bool cpuset_nohz_can_stop_tick(void)
> > > +{
> > > + struct rq *rq;
> > > +
> > > + rq = this_rq();
> > > +
> > > + /* More than one running task need preemption */
> > > + if (rq->nr_running > 1)
> > > + return false;
> > > +
> > > + return true;
> > > +}
> >
> > int sched_needs_cpu(int cpu), seems the right name, matches the existing
> > {rcu,printk,arch}_needs_cpu() functions.
>
> tick_nohz_stop_sched_tick() already handles that by keeping a periodic
> behaviour if one of these conditions are met.

What? tick_nohz_stop_sched_tick() most surely cannot access struct rq,
so it cannot do the nr_running test.

> It has also the upside to restore the periodic behaviour if needed
> from irq return if the tick was stopped.

Again, what?