From: Wanpeng Li <wanpengli@xxxxxxxxxxx> PMU is not exposed to guest by most of 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. ~1.28% vmexit time reduced can be observed by kvm-unit-tests/vmexit.flat on my SKX server. Before patch: vmcall 1559 After patch: vmcall 1539 Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx> --- arch/x86/kvm/vmx/vmx.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 40b1e61..fd526c8 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6441,6 +6441,9 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx) int i, nr_msrs; struct perf_guest_switch_msr *msrs; + if (!vcpu_to_pmu(&vmx->vcpu)->version) + return; + msrs = perf_guest_get_msrs(&nr_msrs); if (!msrs) -- 2.7.4
