From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934442AbdK2RcX (ORCPT ); Wed, 29 Nov 2017 12:32:23 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34300 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933095AbdK2RcV (ORCPT ); Wed, 29 Nov 2017 12:32:21 -0500 Subject: Re: [PATCH v2] KVM: VMX: Cache IA32_DEBUGCTL in memory To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Wanpeng Li , Jim Mattson References: <1511947880-21643-1-git-send-email-wanpeng.li@hotmail.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <4ca54711-99e0-dd28-8957-474e2ce361a7@redhat.com> Date: Wed, 29 Nov 2017 18:32:18 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <1511947880-21643-1-git-send-email-wanpeng.li@hotmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Wed, 29 Nov 2017 17:32:21 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 29.11.2017 10:31, Wanpeng Li wrote: > From: Wanpeng Li > > MSR_IA32_DEBUGCTLMSR is zeroed on VMEXIT, so it is saved/restored > each time during world switch. Jim from Google pointed out that > when running schbench in L2, vmx_vcpu_run will occupy 4% cpu time, > and the 25% of vmx_vcpu_run cpu time is occupied by get_debugctlmsr(). > This patch caches the host IA32_DEBUGCTL MSR and saves/restores > the host IA32_DEBUGCTL msr when guest/host switches to avoid to > save/restore each time during world switch. > > Suggested-by: Jim Mattson > Cc: Paolo Bonzini > Cc: Radim Krčmář > Cc: Jim Mattson > Signed-off-by: Wanpeng Li > --- > v1 -> v2: > * rename to host_debugctlmsr and place it in struct vcpu_struct > * update_debugctlmsr stay in vmx_vcpu_run > > arch/x86/kvm/vmx.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index 8c7e816..d293c29 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -658,6 +658,8 @@ struct vcpu_vmx { > > u32 host_pkru; > > + unsigned long host_debugctlmsr; > + > /* > * Only bits masked by msr_ia32_feature_control_valid_bits can be set in > * msr_ia32_feature_control. FEATURE_CONTROL_LOCKED is always included > @@ -2326,6 +2328,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu) > > vmx_vcpu_pi_load(vcpu, cpu); > vmx->host_pkru = read_pkru(); > + vmx->host_debugctlmsr = get_debugctlmsr(); > } > > static void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu) > @@ -9346,7 +9349,7 @@ static void vmx_arm_hv_timer(struct kvm_vcpu *vcpu) > static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) > { > struct vcpu_vmx *vmx = to_vmx(vcpu); > - unsigned long debugctlmsr, cr3, cr4; > + unsigned long cr3, cr4; > > /* Record the guest's net vcpu time for enforced NMI injections. */ > if (unlikely(!enable_vnmi && > @@ -9399,7 +9402,6 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) > __write_pkru(vcpu->arch.pkru); > > atomic_switch_perf_msrs(vmx); > - debugctlmsr = get_debugctlmsr(); > > vmx_arm_hv_timer(vcpu); > > @@ -9510,8 +9512,8 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) > ); > > /* MSR_IA32_DEBUGCTLMSR is zeroed on vmexit. Restore it if needed */ > - if (debugctlmsr) > - update_debugctlmsr(debugctlmsr); > + if (vmx->host_debugctlmsr) > + update_debugctlmsr(vmx->host_debugctlmsr); > > #ifndef CONFIG_X86_64 > /* > Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb