From 010fd37fddf659ea7525b1191381e6f8c3ccab14 Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Thu, 10 Sep 2020 17:50:41 +0800 Subject: KVM: LAPIC: Reduce world switch latency caused by timer_advance_ns All the checks in lapic_timer_int_injected(), __kvm_wait_lapic_expire(), and these function calls waste cpu cycles when the timer mode is not tscdeadline. We can observe ~1.3% world switch time overhead by kvm-unit-tests/vmexit.flat vmcall testing on AMD server. This patch reduces the world switch latency caused by timer_advance_ns feature when the timer mode is not tscdeadline by simpling move the check against apic->lapic_timer.expired_tscdeadline much earlier. Signed-off-by: Wanpeng Li Message-Id: <1599731444-3525-7-git-send-email-wanpengli@tencent.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx/vmx.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) (limited to 'arch/x86/kvm/vmx/vmx.c') diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index d4dfb7a23a0c..f4cfc18366de 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6800,9 +6800,7 @@ reenter_guest: if (enable_preemption_timer) vmx_update_hv_timer(vcpu); - if (lapic_in_kernel(vcpu) && - vcpu->arch.apic->lapic_timer.timer_advance_ns) - kvm_wait_lapic_expire(vcpu); + kvm_wait_lapic_expire(vcpu); /* * If this vCPU has touched SPEC_CTRL, restore the guest's value if -- cgit v1.2.3