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| author | Wanpeng Li | 2017-12-01 09:15:10 +0100 |
|---|---|---|
| committer | Paolo Bonzini | 2017-12-14 09:26:48 +0100 |
| commit | 9c48d517ce6da398b8cff0603b75b366759023c4 (patch) | |
| tree | f6f20df33a0e12b3ce2275f4a18cde639472350c /arch/x86/kvm/x86.c | |
| parent | KVM: VMX: Cache IA32_DEBUGCTL in memory (diff) | |
| download | kernel-qcow2-linux-9c48d517ce6da398b8cff0603b75b366759023c4.tar.gz kernel-qcow2-linux-9c48d517ce6da398b8cff0603b75b366759023c4.tar.xz kernel-qcow2-linux-9c48d517ce6da398b8cff0603b75b366759023c4.zip | |
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/x86/kvm/x86.c')
| -rw-r--r-- | arch/x86/kvm/x86.c | 3 |
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)) { |