linux-kernel - Re: [PATCH] KVM: x86: add paging gcc optimization

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Message-id: <1331206831.28711.0.camel@offworld>
Date:	Thu, 08 Mar 2012 12:40:31 +0100
From:	Davidlohr Bueso <dave@....org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Marcelo Tosatti <mtosatti@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86: add paging gcc optimization

On Thu, 2012-03-08 at 11:45 +0200, Avi Kivity wrote:
> On 03/07/2012 10:02 PM, Davidlohr Bueso wrote:
> > From: Davidlohr Bueso <dave@....org>
> >
> > Since most guests will have paging enabled for memory management, add likely() and unlikely()
> > optimizations around is_paging() checks.
> >
> > Signed-off-by: Davidlohr Bueso <dave@....org>
> > ---
> >  arch/x86/kvm/mmu.c |    6 +++---
> >  arch/x86/kvm/svm.c |    6 +++---
> >  arch/x86/kvm/vmx.c |   16 ++++++++--------
> >  arch/x86/kvm/x86.c |    8 ++++----
> >  4 files changed, 18 insertions(+), 18 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> > index 4cb1642..84f1e95 100644
> > --- a/arch/x86/kvm/mmu.c
> > +++ b/arch/x86/kvm/mmu.c
> > @@ -3320,7 +3320,7 @@ static int init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
> >  	context->get_pdptr = kvm_pdptr_read;
> >  	context->inject_page_fault = kvm_inject_page_fault;
> >  
> > -	if (!is_paging(vcpu)) {
> > +	if (unlikely(!is_paging(vcpu))) {
> >
> 
> Just change is_paging itself():

Ok, yes, makes more sense. I'll resend the patch. 

Thanks.

> 
>  static inline int is_paging(struct kvm_vcpu *vcpu)
>  {
> -    return kvm_read_cr0_bits(vcpu, X86_CR0_PG);
> +    return likely(kvm_read_cr0_bits(vcpu, X86_CR0_PG));
>   }
> 


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