linux-kernel - Re: [PATCH RFC 1/2] kvm vcpu: Note down pause loop exit

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Date:	Wed, 11 Jul 2012 11:53:36 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	S390 <linux-s390@...r.kernel.org>,
	Carsten Otte <cotte@...ibm.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	KVM <kvm@...r.kernel.org>, chegu vinod <chegu_vinod@...com>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, X86 <x86@...nel.org>,
	Gleb Natapov <gleb@...hat.com>, linux390@...ibm.com,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Joerg Roedel <joerg.roedel@....com>
Subject: Re: [PATCH RFC 1/2] kvm vcpu: Note down pause loop exit

On 07/09/2012 09:20 AM, Raghavendra K T wrote:
> Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
> 
> Noting pause loop exited vcpu helps in filtering right candidate to yield.
> Yielding to same vcpu may result in more wastage of cpu.
> 
>  
>  struct kvm_lpage_info {
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index f75af40..a492f5d 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -3264,6 +3264,7 @@ static int interrupt_window_interception(struct vcpu_svm *svm)
>  
>  static int pause_interception(struct vcpu_svm *svm)
>  {
> +	svm->vcpu.arch.plo.pause_loop_exited = true;
>  	kvm_vcpu_on_spin(&(svm->vcpu));
>  	return 1;
>  }
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 32eb588..600fb3c 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -4945,6 +4945,7 @@ out:
>  static int handle_pause(struct kvm_vcpu *vcpu)
>  {
>  	skip_emulated_instruction(vcpu);
> +	vcpu->arch.plo.pause_loop_exited = true;
>  	kvm_vcpu_on_spin(vcpu);
>  

This code is duplicated.  Should we move it to kvm_vcpu_on_spin?

That means the .plo structure needs to be in common code, but that's not
too bad perhaps.

> index be6d549..07dbd14 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5331,7 +5331,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  
>  	if (req_immediate_exit)
>  		smp_send_reschedule(vcpu->cpu);
> -
> +	vcpu->arch.plo.pause_loop_exited = false;

This adds some tiny overhead to vcpu entry.  You could remove it by
using the vcpu->requests mechanism to clear the flag, since
vcpu->requests is already checked on every entry.

>  	kvm_guest_enter();
>  

-- 
error compiling committee.c: too many arguments to function


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