From: Paolo Bonzini <pbonzini@redhat.com>
To: Wanpeng Li <kernellwp@gmail.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Sean Christopherson <sean.j.christopherson@intel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH v2] KVM: VMX: Micro-optimize vmexit time when not exposing PMU
Date: Sat, 14 Mar 2020 12:00:22 +0100 [thread overview]
Message-ID: <0776e1d0-f0e0-68ef-a07c-9a4884ea1498@redhat.com> (raw)
In-Reply-To: <1584071718-17163-1-git-send-email-wanpengli@tencent.com>
On 13/03/20 04:55, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> 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 <wanpengli@tencent.com>
> ---
> 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
prev parent reply other threads:[~2020-03-15 3:03 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-13 3:55 [PATCH v2] KVM: VMX: Micro-optimize vmexit time when not exposing PMU Wanpeng Li
2020-03-14 11:00 ` Paolo Bonzini [this message]
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