Re: [RFC -v4 PATCH 3/3] kvm: use yield_to instead of sleep in kvm_vcpu_on_spin

[Rik van Riel]

On 01/13/2011 08:16 AM, Avi Kivity wrote:

> > + for (pass = 0; pass< 2&& !yielded; pass++) {
> > + kvm_for_each_vcpu(i, vcpu, kvm) {
> > + struct task_struct *task = vcpu->task;
> > + if (!pass&& i< last_boosted_vcpu) {
> > + i = last_boosted_vcpu;
> > + continue;
> > + } else if (pass&& i> last_boosted_vcpu)
> > + break;
> > + if (vcpu == me)
> > + continue;
> > + if (!task)
> > + continue;
> > + if (waitqueue_active(&vcpu->wq))
> > + continue;
>
> Suppose the vcpu exits at this point, and its task terminates.

Arghh, good point.

> I think the first patch needs some reference counting... I'd move it to
> the outermost KVM_RUN loop to reduce the performance impact.

I don't see how refcounting from that other thread could
possibly help, and I now see that the task_struct_cachep
does not have SLAB_DESTROY_BY_LRU, either :(

What do you have in mind here that would both work and
be acceptable to you as KVM maintainer?

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