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

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Date:   Thu, 18 Jul 2019 19:40:04 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH RESEND] KVM: Boosting vCPUs that are delivering interrupts

On Thu, 18 Jul 2019 at 17:39, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 18/07/19 11:29, Wanpeng Li wrote:
> > On Thu, 18 Jul 2019 at 17:07, Paolo Bonzini <pbonzini@...hat.com> wrote:
> >>
> >> On 18/07/19 10:43, Wanpeng Li wrote:
> >>>>> 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.
> >>
> >> Ok, I was totally blind to that "if" around vcpu->preempted = true, it's
> >> obvious now.
> >>
> >> I think we need two flags then, for example vcpu->preempted and vcpu->ready:
> >>
> >> - kvm_sched_out sets both of them to true iff current->state == TASK_RUNNING
> >>
> >> - kvm_vcpu_kick sets vcpu->ready to true
> >>
> >> - kvm_sched_in clears both of them
>
> ... and also kvm_vcpu_on_spin should check vcpu->ready.  vcpu->preempted
> remains only for use by vmx_vcpu_pi_put.

Done in v2, please have a look. :)

Regards,
Wanpeng Li