linux-kernel - Re: [PATCH v2] KVM: Don't shrink/grow vCPU halt_poll

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Date:   Tue, 8 Oct 2019 09:07:18 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>
Cc:     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>,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH v2] KVM: Don't shrink/grow vCPU halt_poll_ns if host side
 polling is disabled

ping,
On Sun, 29 Sep 2019 at 09:07, Wanpeng Li <kernellwp@...il.com> wrote:
>
> From: Wanpeng Li <wanpengli@...cent.com>
>
> Don't waste cycles to shrink/grow vCPU halt_poll_ns if host
> side polling is disabled.
>
> Acked-by: Marcelo Tosatti <mtosatti@...hat.com>
> Cc: Marcelo Tosatti <mtosatti@...hat.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
> v1 -> v2:
>  * fix coding style
>
>  virt/kvm/kvm_main.c | 29 ++++++++++++++++-------------
>  1 file changed, 16 insertions(+), 13 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e6de315..9d5eed9 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2359,20 +2359,23 @@ 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
>