From 9c48d517ce6da398b8cff0603b75b366759023c4 Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Fri, 1 Dec 2017 00:15:10 -0800 Subject: [PATCH] KVM: X86: Reduce the overhead when lapic_timer_advance is disabled MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit When I run ebizzy in a 32 vCPUs guest on a 32 pCPUs Xeon box, I can observe ~8000 kvm_wait_lapic_expire CurAvg/s through kvm_stat tool even if the advance tscdeadline hrtimer expiration is disabled. Each call to wait_lapic_expire() will consume ~70 cycles when a timer fires since apic_timer_expire() will set expired_tscdeadline and then wait_lapic_expire() will do some caculation before bailing out. So total ~175us per second is lost on this 3.2Ghz machine. This patch reduces the overhead by skipping the function wait_lapic_expire() when lapic_timer_advance is disabled. Cc: Paolo Bonzini Cc: Radim Krčmář Signed-off-by: Wanpeng Li Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 7ea9a57..54d66f2 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7018,7 +7018,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) } trace_kvm_entry(vcpu->vcpu_id); - wait_lapic_expire(vcpu); + if (lapic_timer_advance_ns) + wait_lapic_expire(vcpu); guest_enter_irqoff(); if (unlikely(vcpu->arch.switch_db_regs)) { -- 2.7.4