linux-kernel - Re: [PATCH v2 8/9] KVM: return if kvm_vcpu_wake

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Date:   Thu, 27 Apr 2017 13:41:11 +0200
From:   Andrew Jones <drjones@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Christoffer Dall <cdall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Cornelia Huck <cornelia.huck@...ibm.com>,
        James Hogan <james.hogan@...tec.com>,
        Paul Mackerras <paulus@...abs.org>
Subject: Re: [PATCH v2 8/9] KVM: return if kvm_vcpu_wake_up() did wake up the
 VCPU

On Wed, Apr 26, 2017 at 10:32:26PM +0200, Radim Krčmář wrote:
> No need to kick a VCPU that we have just woken up.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  include/linux/kvm_host.h |  2 +-
>  virt/kvm/kvm_main.c      | 12 ++++++++----
>  2 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 955debd82cf2..38cfe372918c 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -698,7 +698,7 @@ void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn);
>  void kvm_vcpu_block(struct kvm_vcpu *vcpu);
>  void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu);
>  void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu);
> -void kvm_vcpu_wake_up(struct kvm_vcpu *vcpu);
> +bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu);
>  void kvm_vcpu_kick(struct kvm_vcpu *vcpu);
>  int kvm_vcpu_yield_to(struct kvm_vcpu *target);
>  void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 1efb07643035..632f7b3e198c 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -183,8 +183,8 @@ bool kvm_make_all_cpus_request(struct kvm *kvm, unsigned int req)
>  		kvm_make_request(req, vcpu);
>  		cpu = vcpu->cpu;
>  
> -		if (!(req & KVM_REQUEST_NO_WAKEUP))
> -			kvm_vcpu_wake_up(vcpu);
> +		if (!(req & KVM_REQUEST_NO_WAKEUP) && kvm_vcpu_wake_up(vcpu))
> +			continue;
>  
>  		if (cpus != NULL && cpu != -1 && cpu != me &&
>  		      kvm_vcpu_exiting_guest_mode(vcpu) != OUTSIDE_GUEST_MODE)
> @@ -2195,7 +2195,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
>  }
>  EXPORT_SYMBOL_GPL(kvm_vcpu_block);
>  
> -void kvm_vcpu_wake_up(struct kvm_vcpu *vcpu)
> +bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu)
>  {
>  	struct swait_queue_head *wqp;
>  
> @@ -2203,8 +2203,10 @@ void kvm_vcpu_wake_up(struct kvm_vcpu *vcpu)
>  	if (swait_active(wqp)) {
>  		swake_up(wqp);
>  		++vcpu->stat.halt_wakeup;
> +		return true;
>  	}
>  
> +	return false;
>  }
>  EXPORT_SYMBOL_GPL(kvm_vcpu_wake_up);
>  
> @@ -2216,7 +2218,9 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
>  	int me;
>  	int cpu = vcpu->cpu;
>  
> -	kvm_vcpu_wake_up(vcpu);
> +	if (kvm_vcpu_wake_up(vcpu))
> +		return;
> +
>  	me = get_cpu();
>  	if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
>  		if (kvm_arch_vcpu_should_kick(vcpu))
> -- 
> 2.12.2
>

Reviewed-by: Andrew Jones <drjones@...hat.com>