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

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Message-ID: <CANRm+CxV0c3RSidV_GQtVuQ5fUUCT8vM=5LpodgDg+dFWhkH3w@mail.gmail.com>
Date:   Thu, 18 Jul 2019 17:29:19 +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 17:07, 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
>
> This way, vmx_vcpu_pi_load can keep looking at preempted only (it
> handles voluntary preemption in pi_pre_block/pi_post_block).
>
> Also, kvm_s390_vcpu_wakeup can be changed to use kvm_vcpu_wake_up, which
> is nice.

Will do. :)

Wanpeng