Re: [PATCH 17/24] sched/fair: Implement delayed dequeue

[Sean Christopherson <seanjc@google.com>]

On Thu, Oct 10, 2024, Mike Galbraith wrote:
> On Wed, 2024-10-09 at 19:49 -0700, Sean Christopherson wrote:
> >
> > Any thoughts on how best to handle this?  The below hack-a-fix resolves the issue,
> > but it's obviously not appropriate.  KVM uses vcpu->preempted for more than just
> > posted interrupts, so KVM needs equivalent functionality to current->on-rq as it
> > was before this commit.
> >
> > @@ -6387,7 +6390,7 @@ static void kvm_sched_out(struct preempt_notifier *pn,
> >  
> >         WRITE_ONCE(vcpu->scheduled_out, true);
> >  
> > -       if (current->on_rq && vcpu->wants_to_run) {
> > +       if (se_runnable(&current->se) && vcpu->wants_to_run) {
> >                 WRITE_ONCE(vcpu->preempted, true);
> >                 WRITE_ONCE(vcpu->ready, true);
> >         }
> 
> Why is that deemed "obviously not appropriate"?  ->on_rq in and of
> itself meaning only "on rq" doesn't seem like a bad thing.

Doh, my wording was unclear.  I didn't mean the logic was inappropriate, I meant
that KVM shouldn't be poking into an internal sched/ helper.