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authorWanpeng Li <kernellwp@gmail.com>2017-12-01 00:15:10 -0800
committerPaolo Bonzini <pbonzini@redhat.com>2017-12-14 09:26:48 +0100
commit9c48d517ce6da398b8cff0603b75b366759023c4 (patch)
treef6f20df33a0e12b3ce2275f4a18cde639472350c /arch
parent74c55931c71352317ae0f5736ee9e4ca07ba4238 (diff)
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: Wanpeng Li <wanpeng.li@hotmail.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kvm/x86.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7ea9a57b0684..54d66f238e20 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)) {