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Commit 9c48d517 authored by Wanpeng Li's avatar Wanpeng Li Committed by Paolo Bonzini
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KVM: X86: Reduce the overhead when lapic_timer_advance is disabled 



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 <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: default avatarWanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 74c55931

arch/x86/kvm/x86.c

+2 −1
Original line number Diff line number Diff line
@@ -7018,6 +7018,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) 
	}



	trace_kvm_entry(vcpu->vcpu_id);

	if (lapic_timer_advance_ns)

		wait_lapic_expire(vcpu);

	guest_enter_irqoff();