* [PATCH v2] KVM: VMX: Micro-optimize vmexit time when not exposing PMU
@ 2020-03-13 3:55 Wanpeng Li
2020-03-14 11:00 ` Paolo Bonzini
0 siblings, 1 reply; 2+ messages in thread
From: Wanpeng Li @ 2020-03-13 3:55 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: Paolo Bonzini, Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel
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)
--
2.7.4
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] KVM: VMX: Micro-optimize vmexit time when not exposing PMU
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
0 siblings, 0 replies; 2+ messages in thread
From: Paolo Bonzini @ 2020-03-14 11:00 UTC (permalink / raw)
To: Wanpeng Li, linux-kernel, kvm
Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel
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
^ permalink raw reply [flat|nested] 2+ messages in thread
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2020-03-14 11:00 ` Paolo Bonzini
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