Messages in this thread Patch in this message | | | Subject | Re: [RFC] KVM: optimize the kvm_vcpu_on_spin | From | David Hildenbrand <> | Date | Mon, 31 Jul 2017 13:31:45 +0200 |
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[no idea if this change makes sense (and especially if it has any bad side effects), do you have performance numbers? I'll just have a look at the general structure of the patch in the meanwhile]
> +bool kvm_arch_vcpu_spin_kernmode(struct kvm_vcpu *vcpu)
kvm_arch_vcpu_in_kernel() ?
> +{ > + return kvm_x86_ops->get_cpl(vcpu) == 0; > +} > + > int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu) > { > return kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE; > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 648b34c..f8f0d74 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -272,6 +272,9 @@ struct kvm_vcpu { > } spin_loop; > #endif > bool preempted; > + /* If vcpu is in kernel-mode when preempted */ > + bool in_kernmode; > +
Why do you have to store that ...
[...]> + me->in_kernmode = kvm_arch_vcpu_spin_kernmode(me); > kvm_vcpu_set_in_spin_loop(me, true); > /* > * We boost the priority of a VCPU that is runnable but not > @@ -2351,6 +2353,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) > continue; > if (swait_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu)) > continue; > + if (me->in_kernmode && !vcpu->in_kernmode)
Wouldn't it be easier to simply have
in_kernel = kvm_arch_vcpu_in_kernel(me); ... if (in_kernel && !kvm_arch_vcpu_in_kernel(vcpu)) ...
> + continue; > if (!kvm_vcpu_eligible_for_directed_yield(vcpu)) > continue; > > @@ -4009,8 +4013,11 @@ static void kvm_sched_out(struct preempt_notifier *pn, > { > struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn); > > - if (current->state == TASK_RUNNING) > + if (current->state == TASK_RUNNING) { > vcpu->preempted = true; > + vcpu->in_kernmode = kvm_arch_vcpu_spin_kernmode(vcpu); > + } > +
so you don't have to do this change, too.
> kvm_arch_vcpu_put(vcpu); > } > >
--
Thanks,
David
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