From b6c4bc659c6f3b7f2b6c3a330ae36f1cfd69d73e Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Mon, 20 May 2019 16:18:09 +0800 Subject: KVM: LAPIC: Optimize timer latency further MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Advance lapic timer tries to hidden the hypervisor overhead between the host emulated timer fires and the guest awares the timer is fired. However, it just hidden the time between apic_timer_fn/handle_preemption_timer -> wait_lapic_expire, instead of the real position of vmentry which is mentioned in the orignial commit d0659d946be0 ("KVM: x86: add option to advance tscdeadline hrtimer expiration"). There is 700+ cpu cycles between the end of wait_lapic_expire and before world switch on my haswell desktop. This patch tries to narrow the last gap(wait_lapic_expire -> world switch), it takes the real overhead time between apic_timer_fn/handle_preemption_timer and before world switch into consideration when adaptively tuning timer advancement. The patch can reduce 40% latency (~1600+ cycles to ~1000+ cycles on a haswell desktop) for kvm-unit-tests/tscdeadline_latency when testing busy waits. Cc: Paolo Bonzini Cc: Radim Krčmář Cc: Sean Christopherson Cc: Liran Alon Reviewed-by: Sean Christopherson Signed-off-by: Wanpeng Li Signed-off-by: Paolo Bonzini --- arch/x86/kvm/lapic.c | 3 ++- arch/x86/kvm/lapic.h | 2 +- arch/x86/kvm/svm.c | 4 ++++ arch/x86/kvm/vmx/vmx.c | 4 ++++ arch/x86/kvm/x86.c | 3 --- 5 files changed, 11 insertions(+), 5 deletions(-) (limited to 'arch') diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index f8615872ae64..fcf42a340790 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1531,7 +1531,7 @@ static inline void adjust_lapic_timer_advance(struct kvm_vcpu *vcpu, apic->lapic_timer.timer_advance_ns = timer_advance_ns; } -void wait_lapic_expire(struct kvm_vcpu *vcpu) +void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu) { struct kvm_lapic *apic = vcpu->arch.apic; u64 guest_tsc, tsc_deadline; @@ -1553,6 +1553,7 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu) if (unlikely(!apic->lapic_timer.timer_advance_adjust_done)) adjust_lapic_timer_advance(vcpu, apic->lapic_timer.advance_expire_delta); } +EXPORT_SYMBOL_GPL(kvm_wait_lapic_expire); static void start_sw_tscdeadline(struct kvm_lapic *apic) { diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h index 3e72a255543d..f974a3d5a44d 100644 --- a/arch/x86/kvm/lapic.h +++ b/arch/x86/kvm/lapic.h @@ -220,7 +220,7 @@ static inline int kvm_lapic_latched_init(struct kvm_vcpu *vcpu) bool kvm_apic_pending_eoi(struct kvm_vcpu *vcpu, int vector); -void wait_lapic_expire(struct kvm_vcpu *vcpu); +void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu); bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq, struct kvm_vcpu **dest_vcpu); diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index 5beca1030c9a..a7ea34bed3fe 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -5643,6 +5643,10 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu) clgi(); kvm_load_guest_xcr0(vcpu); + if (lapic_in_kernel(vcpu) && + vcpu->arch.apic->lapic_timer.timer_advance_ns) + kvm_wait_lapic_expire(vcpu); + /* * If this vCPU has touched SPEC_CTRL, restore the guest's value if * it's non-zero. Since vmentry is serialising on affected CPUs, there diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index b93e36ddee5e..b35b3800a3c0 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6445,6 +6445,10 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu) vmx_update_hv_timer(vcpu); + if (lapic_in_kernel(vcpu) && + vcpu->arch.apic->lapic_timer.timer_advance_ns) + kvm_wait_lapic_expire(vcpu); + /* * If this vCPU has touched SPEC_CTRL, restore the guest's value if * it's non-zero. Since vmentry is serialising on affected CPUs, there diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 7a26aa5b0861..2a713a74ca2e 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7922,9 +7922,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) } trace_kvm_entry(vcpu->vcpu_id); - if (lapic_in_kernel(vcpu) && - vcpu->arch.apic->lapic_timer.timer_advance_ns) - wait_lapic_expire(vcpu); guest_enter_irqoff(); fpregs_assert_state_consistent(); -- cgit v1.2.3