On Thu, 28 Jul 2011, Yong Zhang wrote:
> On Wed, Jul 27, 2011 at 11:30:08AM -0700, Paul E. McKenney wrote:
> > o Tasks awakening outside of migrate-disable regions will pick
> > the CPU running the lowest-priority task, whether or not this
> > task is in migrate-disable state. (At least I don't see
> > anything in 3.0-rt3 that looks like a scheduling decision
> > based on ->migrate_disable, perhaps due to blindness.)
>
> I'm also confused here, seems we just disable migration for RT task.
> migrate_disable()
> {
> ...
> if (p->sched_class->set_cpus_allowed)
> p->sched_class->set_cpus_allowed(p, mask);
> p->rt.nr_cpus_allowed = cpumask_weight(mask);
> ...
> }
>
> Shouldn't we also forbid migration on !RT task?
We do. Just RT is the only sched class which has a set_cpus_allowed()
callback implemented and want's an update to its rt.nr_cpus_allowed
field.
if (!p->migrate_disable) {
if (p->sched_class && p->sched_class->set_cpus_allowed)
p->sched_class->set_cpus_allowed(p, new_mask);
p->rt.nr_cpus_allowed = cpumask_weight(new_mask);
}
The general part is here:
cpumask_copy(&p->cpus_allowed, new_mask);
And tsk_cpus_allowed() does:
{
if (p->migrate_disable)
return cpumask_of(task_cpu(p));
return &p->cpus_allowed;
}
which is the relevant information to keep any task independent of it's
sched class pinned.
Thanks,
tglx
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