Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU mask

[Peter Zijlstra]

On Thu, Apr 06, 2017 at 11:35:45AM +0200, Peter Zijlstra wrote:
> On Thu, Apr 06, 2017 at 10:01:39AM +0200, Ingo Molnar wrote:
> > I.e. just have a counter and these two APIs:
> > 
> >         static inline void migrate_disable(void)
> >         {
> >                 current->migration_disabled++;
> >         }
> > 
> >         ...
> > 
> >         static inline void migrate_enable(void)
> >         {
> >                 current->migration_disabled--;
> >         }
> > 
> > ... and make sure the scheduler migration code plus the CPU hotplug code 
> > considers 
> > the counter.
> > 
> > Would this work, and would this be the simplest all around solution?
> 
> If you want to add expensive bits to hot paths like wakeups ... :/

Hmm, doesn't that get us back to exactly where we were: ?

tsk_cpus_allowed() 
{
        if (!tsk->migration_disabled)
                return tsk->cpus_allowed;
        else
                return cpumask_of(task_cpu(tsk));
}