From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH] KVM: VMX: Conditionally reload debug register 6 Date: Tue, 01 Sep 2009 13:43:14 +0200 Message-ID: <4A9D08D2.1020407@siemens.com> References: <1251805232-16885-1-git-send-email-avi@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , "kvm@vger.kernel.org" To: Avi Kivity Return-path: Received: from goliath.siemens.de ([192.35.17.28]:24912 "EHLO goliath.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753950AbZIALn0 (ORCPT ); Tue, 1 Sep 2009 07:43:26 -0400 In-Reply-To: <1251805232-16885-1-git-send-email-avi@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > Only reload debug register 6 if we're running with the guest's > debug registers. Saves around 150 cycles from the guest lightweight > exit path. > > Signed-off-by: Avi Kivity > --- > arch/x86/kvm/vmx.c | 6 ++++-- > 1 files changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index 05cd554..70b0c54 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -3629,7 +3629,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu) > */ > vmcs_writel(HOST_CR0, read_cr0()); > > - set_debugreg(vcpu->arch.dr6, 6); > + if (vcpu->arch.switch_db_regs) > + set_debugreg(vcpu->arch.dr6, 6); > > asm( > /* Store host registers */ > @@ -3731,7 +3732,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu) > | (1 << VCPU_EXREG_PDPTR)); > vcpu->arch.regs_dirty = 0; > > - get_debugreg(vcpu->arch.dr6, 6); > + if (vcpu->arch.switch_db_regs) > + get_debugreg(vcpu->arch.dr6, 6); > > vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD); > if (vmx->rmode.irq.pending) That reduces the emulation quality as vcpu->arch.switch_db_regs is only set if some breakpoint is active while dr6 has its use also when that is not the case). Jan -- Siemens AG, Corporate Technology, CT SE 2 Corporate Competence Center Embedded Linux