linux-kernel - Re: [PATCH] KVM: MMU: increment stats after event occurrence

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Date:	Fri, 13 Jan 2012 13:56:00 +0100
From:	Davidlohr Bueso <dave@....org>
To:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	lkml <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: MMU: increment stats after event occurrence

On Fri, 2012-01-13 at 10:24 +0900, Takuya Yoshikawa wrote:
> (2012/01/13 10:08), Davidlohr Bueso wrote:
> > From: Davidlohr Bueso<dave@....org>
> >
> > It makes more sense to actually increment statistics for tlb flushes and page table entry updates after such _events_ occur, instead of before.
> 
> Why?
> 
>From a logical point of view its better to increase stats once the event
is processed - usually because it can fail and therefore the stats would
be incorrect. 

> 	Takuya
> 
> >
> > Signed-off-by: Davidlohr Bueso<dave@....org>
> > ---
> >   arch/x86/kvm/mmu.c |    4 ++--
> >   1 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> > index 2a2a9b4..0b7008e 100644
> > --- a/arch/x86/kvm/mmu.c
> > +++ b/arch/x86/kvm/mmu.c
> > @@ -3130,8 +3130,8 @@ static int nonpaging_init_context(struct kvm_vcpu *vcpu,
> >
> >   void kvm_mmu_flush_tlb(struct kvm_vcpu *vcpu)
> >   {
> > -	++vcpu->stat.tlb_flush;
> >   	kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
> > +	++vcpu->stat.tlb_flush;
> >   }
> >
> >   static void paging_new_cr3(struct kvm_vcpu *vcpu)
> > @@ -3486,8 +3486,8 @@ static void mmu_pte_write_new_pte(struct kvm_vcpu *vcpu,
> >   		return;
> >           }
> >
> > -	++vcpu->kvm->stat.mmu_pte_updated;
> >   	vcpu->arch.mmu.update_pte(vcpu, sp, spte, new);
> > +	++vcpu->kvm->stat.mmu_pte_updated;
> >   }
> >
> >   static bool need_remote_flush(u64 old, u64 new)
> 
> 


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