linux-kernel - Re: [PATCH] KVM: Don't shrink/grow vCPU halt_poll

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Date:   Sun, 29 Sep 2019 09:03:57 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] KVM: Don't shrink/grow vCPU halt_poll_ns if host side
 polling is disabled

On Sat, 28 Sep 2019 at 01:24, Marcelo Tosatti <mtosatti@...hat.com> wrote:
>
> On Fri, Sep 27, 2019 at 04:27:02PM +0800, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > Don't waste cycles to shrink/grow vCPU halt_poll_ns if host
> > side polling is disabled.
> >
> > Cc: Marcelo Tosatti <mtosatti@...hat.com>
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> > ---
> >  virt/kvm/kvm_main.c | 28 +++++++++++++++-------------
> >  1 file changed, 15 insertions(+), 13 deletions(-)
> >
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index e6de315..b368be4 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -2359,20 +2359,22 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
> >       kvm_arch_vcpu_unblocking(vcpu);
> >       block_ns = ktime_to_ns(cur) - ktime_to_ns(start);
> >
> > -     if (!vcpu_valid_wakeup(vcpu))
> > -             shrink_halt_poll_ns(vcpu);
> > -     else if (halt_poll_ns) {
> > -             if (block_ns <= vcpu->halt_poll_ns)
> > -                     ;
> > -             /* we had a long block, shrink polling */
> > -             else if (vcpu->halt_poll_ns && block_ns > halt_poll_ns)
> > +     if (!kvm_arch_no_poll(vcpu)) {
> > +             if (!vcpu_valid_wakeup(vcpu))
> >                       shrink_halt_poll_ns(vcpu);
> > -             /* we had a short halt and our poll time is too small */
> > -             else if (vcpu->halt_poll_ns < halt_poll_ns &&
> > -                     block_ns < halt_poll_ns)
> > -                     grow_halt_poll_ns(vcpu);
> > -     } else
> > -             vcpu->halt_poll_ns = 0;
> > +             else if (halt_poll_ns) {
> > +                     if (block_ns <= vcpu->halt_poll_ns)
> > +                             ;
> > +                     /* we had a long block, shrink polling */
> > +                     else if (vcpu->halt_poll_ns && block_ns > halt_poll_ns)
> > +                             shrink_halt_poll_ns(vcpu);
> > +                     /* we had a short halt and our poll time is too small */
> > +                     else if (vcpu->halt_poll_ns < halt_poll_ns &&
> > +                             block_ns < halt_poll_ns)
> > +                             grow_halt_poll_ns(vcpu);
> > +             } else
> > +                     vcpu->halt_poll_ns = 0;
> > +     }
> >
> >       trace_kvm_vcpu_wakeup(block_ns, waited, vcpu_valid_wakeup(vcpu));
> >       kvm_arch_vcpu_block_finish(vcpu);
> > --
> > 2.7.4
>
> Looks good.

I will add your ACK in v2.

    Wanpeng