From: Wanpeng Li <wanpengli@xxxxxxxxxxx> Let's treat lapic_timer_advance_ns automatically tune logic as hypervisor overhead, move it before wait_lapic_expire instead of between wait_lapic_expire and the world switch, the wait duration should be calculated by the up-to-date guest_tsc after the overhead of automatically tune logic. This patch reduces ~30+ cycles for kvm-unit-tests/tscdeadline-latency when testing busy waits. Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx> --- arch/x86/kvm/lapic.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index c0ebef560bd1..552d2acf89ab 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1598,11 +1598,12 @@ static void __kvm_wait_lapic_expire(struct kvm_vcpu *vcpu) guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc()); apic->lapic_timer.advance_expire_delta = guest_tsc - tsc_deadline; - if (guest_tsc < tsc_deadline) - __wait_lapic_expire(vcpu, tsc_deadline - guest_tsc); - if (lapic_timer_advance_dynamic) adjust_lapic_timer_advance(vcpu, apic->lapic_timer.advance_expire_delta); + + guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc()); + if (guest_tsc < tsc_deadline) + __wait_lapic_expire(vcpu, tsc_deadline - guest_tsc); } void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu) -- 2.25.1
