Re: [RFC] sched/core: Don't schedule threads on pre-empted vcpus

[Rohit Jain]

Hi Peter,


On 05/04/2018 02:47 AM, Peter Zijlstra wrote:
> On Wed, May 02, 2018 at 01:52:10PM -0700, Rohit Jain wrote:
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 5e10aae..75d1ecf 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -4033,6 +4033,9 @@ int idle_cpu(int cpu)
> >   		return 0;
> >   #endif
> >   
> > +	if (vcpu_is_preempted(cpu))
> > +		return 0;
> > +
> >   	return 1;
> >   }
> Basically OK with this, but did you consider idle_cpu() usage outside of
> select_idle_sibling()?
>
> For instance, I think got_nohz_idle_kick() isn't quite right with this
> on. Similarly for scheduler_tick(), that wants the actual idle state.

As far as intent is concerned, yes I agree you might be right. I left
the VM running for a couple of days, didn't see anything weird however.

We could add a check at each of those places or something to that effect
if this is an issue. Please let me know how you want to proceed.