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([2001:b07:6468:f312:7de8:5d90:2370:d1ac]) by smtp.gmail.com with ESMTPSA id r9sm13830690wma.47.2020.03.14.04.00.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 14 Mar 2020 04:00:22 -0700 (PDT) Subject: Re: [PATCH v2] KVM: VMX: Micro-optimize vmexit time when not exposing PMU To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel References: <1584071718-17163-1-git-send-email-wanpengli@tencent.com> From: Paolo Bonzini Message-ID: <0776e1d0-f0e0-68ef-a07c-9a4884ea1498@redhat.com> Date: Sat, 14 Mar 2020 12:00:22 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <1584071718-17163-1-git-send-email-wanpengli@tencent.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/03/20 04:55, Wanpeng Li wrote: > From: Wanpeng Li > > PMU is not exposed to guest by most of products from cloud providers since the > bad performance of PMU emulation and security concern. However, it calls > perf_guest_switch_get_msrs() and clear_atomic_switch_msr() unconditionally > even if PMU is not exposed to the guest before each vmentry. > > ~2% vmexit time reduced can be observed by kvm-unit-tests/vmexit.flat on my > SKX server. > > Before patch: > vmcall 1559 > > After patch: > vmcall 1529 > > Signed-off-by: Wanpeng Li > --- > v1 -> v2: > * move the check before atomic_switch_perf_msrs > > arch/x86/kvm/vmx/vmx.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 40b1e61..b20423c 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -6567,7 +6567,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu) > > pt_guest_enter(vmx); > > - atomic_switch_perf_msrs(vmx); > + if (vcpu_to_pmu(vcpu)->version) > + atomic_switch_perf_msrs(vmx); > atomic_switch_umwait_control_msr(vmx); > > if (enable_preemption_timer) > Queued, thanks. Paolo