Re: [PATCH 12/35] autonuma: CPU follow memory algorithm

[Rik van Riel]

On 05/29/2012 09:00 AM, Peter Zijlstra wrote:
> On Fri, 2012-05-25 at 19:02 +0200, Andrea Arcangeli wrote:
> > @@ -3274,6 +3268,8 @@ need_resched:
> >
> >          post_schedule(rq);
> >
> > +       sched_autonuma_balance();
> > +
> >          sched_preempt_enable_no_resched();
> >          if (need_resched())
> >                  goto need_resched;
>
>
>
> > +void sched_autonuma_balance(void)
> > +{
>
> > +       for_each_online_node(nid) {
> > +       }
>
> > +       for_each_online_node(nid) {
> > +               for_each_cpu_and(cpu, cpumask_of_node(nid), allowed) {
>
>
> > +               }
> > +       }
>
> > +       stop_one_cpu(this_cpu, migration_cpu_stop,&arg);
> > +}
>
> NAK
>
> You do _NOT_ put a O(nr_cpus) or even O(nr_nodes) loop in the middle of
> schedule().
>
> I see you've made it conditional, but schedule() taking that long --
> even occasionally -- is just not cool.
>
> schedule() calling schedule() is also an absolute abomination.
>
> You were told to fix this several times..

Do you have any suggestions for how Andrea could fix this?

Pairwise comparisons with a busy CPU/node?

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