Re: [PATCH RESEND] KVM: Boosting vCPUs that are delivering interrupts

[Wanpeng Li]

On Thu, 18 Jul 2019 at 16:34, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> On 18/07/19 10:15, Christian Borntraeger wrote:
> >
> >
> > On 18.07.19 09:59, Paolo Bonzini wrote:
> >> On 12/07/19 09:15, Wanpeng Li wrote:
> >>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> >>> index b4ab59d..2c46705 100644
> >>> --- a/virt/kvm/kvm_main.c
> >>> +++ b/virt/kvm/kvm_main.c
> >>> @@ -2404,8 +2404,10 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
> >>>     int me;
> >>>     int cpu = vcpu->cpu;
> >>>
> >>> -   if (kvm_vcpu_wake_up(vcpu))
> >>> +   if (kvm_vcpu_wake_up(vcpu)) {
> >>> +           vcpu->preempted = true;
> >>>             return;
> >>> +   }
> >>>
> >>>     me = get_cpu();
> >>>     if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
> >>>
> >>
> >> Who is resetting vcpu->preempted to false in this case?  This also
> >> applies to s390 in fact.
> >
> > Isnt that done by the sched_in handler?
>
> I am a bit confused because, if it is done by the sched_in later, I
> don't understand why the sched_out handler hasn't set vcpu->preempted
> already.
>
> The s390 commit message is not very clear, but it talks about "a former
> sleeping cpu" that "gave up the cpu voluntarily".  Does "voluntarily"
> that mean it is in kvm_vcpu_block?  But then at least for x86 it would

see the prepare_to_swait_exlusive() in kvm_vcpu_block(), the task will
be set in TASK_INTERRUPTIBLE state, kvm_sched_out will set
vcpu->preempted to true iff current->state == TASK_RUNNING.

Regards,
Wanpeng Li