linux-kernel - Re: [PATCH 3/9] KVM: VMX: make PLE window per-vcpu

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Message-ID: <53F44AAD.5020203@redhat.com>
Date:	Wed, 20 Aug 2014 09:13:49 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>,
	kvm@...r.kernel.org
CC:	linux-kernel@...r.kernel.org, Gleb Natapov <gleb@...nel.org>,
	Raghavendra KT <raghavendra.kt@...ux.vnet.ibm.com>,
	Vinod Chegu <chegu_vinod@...com>, Hui-Zhi <hui-zhi.zhao@...com>
Subject: Re: [PATCH 3/9] KVM: VMX: make PLE window per-vcpu

Il 19/08/2014 22:35, Radim Krčmář ha scritto:
> Change PLE window into per-vcpu variable, seeded from module parameter,
> to allow greater flexibility.
> 
> Brings in a small overhead on every vmentry.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  I've been thinking about a general hierarchical per-vcpu variable model,
>  but it's hard to have current performance and sane code.
> 
>  arch/x86/kvm/vmx.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 2b306f9..eaa5574 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -484,6 +484,9 @@ struct vcpu_vmx {
>  
>  	/* Support for a guest hypervisor (nested VMX) */
>  	struct nested_vmx nested;
> +
> +	/* Dynamic PLE window. */
> +	int ple_window;
>  };
>  
>  enum segment_cache_field {
> @@ -4403,6 +4406,7 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
>  	if (ple_gap) {
>  		vmcs_write32(PLE_GAP, ple_gap);
>  		vmcs_write32(PLE_WINDOW, ple_window);

Is this necessary?

> +		vmx->ple_window = ple_window;
>  	}
>  
>  	vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK, 0);
> @@ -7387,6 +7391,9 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
>  	if (vmx->emulation_required)
>  		return;
>  
> +	if (ple_gap)
> +		vmcs_write32(PLE_WINDOW, vmx->ple_window);
> +
>  	if (vmx->nested.sync_shadow_vmcs) {
>  		copy_vmcs12_to_shadow(vmx);
>  		vmx->nested.sync_shadow_vmcs = false;
> 

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