From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCHv6 6/8] kvm: only sync when attention bits set Date: Tue, 12 Jun 2012 19:27:48 -0300 Message-ID: <20120612222748.GB1973@amt.cnet> References: <56ee14064ef307b7075f6977122781456cab5165.1338474301.git.mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: x86@kernel.org, kvm@vger.kernel.org, Ingo Molnar , "H. Peter Anvin" , Avi Kivity , gleb@redhat.com, Linus Torvalds , linux-kernel@vger.kernel.org, Thomas Gleixner To: "Michael S. Tsirkin" Return-path: Content-Disposition: inline In-Reply-To: <56ee14064ef307b7075f6977122781456cab5165.1338474301.git.mst@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Sun, Jun 03, 2012 at 10:28:29AM +0300, Michael S. Tsirkin wrote: > Commit eb0dc6d0368072236dcd086d7fdc17fd3c4574d4 introduced apic > attention bitmask but kvm still syncs lapic unconditionally. > As that commit suggested and in anticipation of adding more attention > bits, only sync lapic if(apic_attention). > > Signed-off-by: Michael S. Tsirkin > --- > arch/x86/kvm/x86.c | 3 ++- > 1 files changed, 2 insertions(+), 1 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index be6d549..2f70861 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -5388,7 +5388,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > if (unlikely(vcpu->arch.tsc_always_catchup)) > kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); > > - kvm_lapic_sync_from_vapic(vcpu); > + if (unlikely(vcpu->arch.apic_attention)) > + kvm_lapic_sync_from_vapic(vcpu); void kvm_lapic_sync_from_vapic(struct kvm_vcpu *vcpu) { u32 data; void *vapic; if (!test_bit(KVM_APIC_CHECK_VAPIC, &vcpu->arch.apic_attention)) return; Please use unlikely more carefully, when a gain is measureable: http://lwn.net/Articles/420019/