[Devel,v1] KVM: x86: avoid redundant REQ_EVENT

Submitted by Denis Plotnikov on Jan. 10, 2017, 4:14 p.m.

Details

Message ID 20170110161401.39107-1-dplotnikov@virtuozzo.com
State New
Series "KVM: x86: avoid redundant REQ_EVENT"
Headers show

Commit Message

Denis Plotnikov Jan. 10, 2017, 4:14 p.m.
When processing KVM_REQ_EVENT, apic_update_ppr is called which may set
KVM_REQ_EVENT again if the recalculated value of PPR becomes smaller
than the previous one. This results in cancelling the guest entry and
reiterating in vcpu_enter_guest.

However this is unnecessary because at this point KVM_REQ_EVENT is
already being processed and there are no other changes in the lapic
that may require full-fledged state recalculation.

This situation is often hit on systems with TPR shadow, where the
TPR can be updated by the guest without a vmexit, so that the first
apic_update_ppr to notice it is exactly the one called while
processing KVM_REQ_EVENT.

To avoid it, introduce a parameter in apic_update_ppr allowing to
suppress setting of KVM_REQ_EVENT, and use it on the paths called from
KVM_REQ_EVENT processing.
Also add the parameter to kvm_cpu_get_interrupt to be passed through
to apic_update_ppr to make sure the supression of KVM_REQ_EVENT is done
in the KVM_REQ_EVENT processing path only.

This microoptimization gives 10% performance increase on a synthetic
test doing a lot of IPC in Windows using window messages.

Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
---
 arch/x86/include/asm/kvm_host.h |  2 +-
 arch/x86/kvm/irq.c              |  8 ++++----
 arch/x86/kvm/lapic.c            | 26 +++++++++++++-------------
 arch/x86/kvm/lapic.h            |  4 ++--
 arch/x86/kvm/vmx.c              |  2 +-
 arch/x86/kvm/x86.c              |  2 +-
 6 files changed, 22 insertions(+), 22 deletions(-)

Patch hide | download patch | download mbox

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ee50557..fb13c87 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1239,7 +1239,7 @@  void kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte);
 int kvm_cpu_has_injectable_intr(struct kvm_vcpu *v);
 int kvm_cpu_has_interrupt(struct kvm_vcpu *vcpu);
 int kvm_arch_interrupt_allowed(struct kvm_vcpu *vcpu);
-int kvm_cpu_get_interrupt(struct kvm_vcpu *v);
+int kvm_cpu_get_interrupt(struct kvm_vcpu *v, bool make_req);
 void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event);
 void kvm_vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu);
 void kvm_arch_mmu_notifier_invalidate_page(struct kvm *kvm,
diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
index 95fcc7b..d434ad9 100644
--- a/arch/x86/kvm/irq.c
+++ b/arch/x86/kvm/irq.c
@@ -82,7 +82,7 @@  int kvm_cpu_has_injectable_intr(struct kvm_vcpu *v)
 	if (kvm_vcpu_apicv_active(v))
 		return 0;
 
-	return kvm_apic_has_interrupt(v) != -1; /* LAPIC */
+	return kvm_apic_has_interrupt(v, false) != -1; /* LAPIC */
 }
 
 /*
@@ -97,7 +97,7 @@  int kvm_cpu_has_interrupt(struct kvm_vcpu *v)
 	if (kvm_cpu_has_extint(v))
 		return 1;
 
-	return kvm_apic_has_interrupt(v) != -1;	/* LAPIC */
+	return kvm_apic_has_interrupt(v, true) != -1;	/* LAPIC */
 }
 EXPORT_SYMBOL_GPL(kvm_cpu_has_interrupt);
 
@@ -122,7 +122,7 @@  static int kvm_cpu_get_extint(struct kvm_vcpu *v)
 /*
  * Read pending interrupt vector and intack.
  */
-int kvm_cpu_get_interrupt(struct kvm_vcpu *v)
+int kvm_cpu_get_interrupt(struct kvm_vcpu *v, bool make_req)
 {
 	int vector;
 
@@ -134,7 +134,7 @@  int kvm_cpu_get_interrupt(struct kvm_vcpu *v)
 	if (vector != -1)
 		return vector;			/* PIC */
 
-	return kvm_get_apic_interrupt(v);	/* APIC */
+	return kvm_get_apic_interrupt(v, make_req);	/* APIC */
 }
 EXPORT_SYMBOL_GPL(kvm_cpu_get_interrupt);
 
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index ff8d0fd..77ad90e 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -561,7 +561,7 @@  static void pv_eoi_clr_pending(struct kvm_vcpu *vcpu)
 	__clear_bit(KVM_APIC_PV_EOI_PENDING, &vcpu->arch.apic_attention);
 }
 
-static void apic_update_ppr(struct kvm_lapic *apic)
+static void apic_update_ppr(struct kvm_lapic *apic, bool make_req)
 {
 	u32 tpr, isrv, ppr, old_ppr;
 	int isr;
@@ -581,7 +581,7 @@  static void apic_update_ppr(struct kvm_lapic *apic)
 
 	if (old_ppr != ppr) {
 		apic_set_reg(apic, APIC_PROCPRI, ppr);
-		if (ppr < old_ppr)
+		if (make_req && ppr < old_ppr)
 			kvm_make_request(KVM_REQ_EVENT, apic->vcpu);
 	}
 }
@@ -589,7 +589,7 @@  static void apic_update_ppr(struct kvm_lapic *apic)
 static void apic_set_tpr(struct kvm_lapic *apic, u32 tpr)
 {
 	apic_set_reg(apic, APIC_TASKPRI, tpr);
-	apic_update_ppr(apic);
+	apic_update_ppr(apic, true);
 }
 
 static bool kvm_apic_broadcast(struct kvm_lapic *apic, u32 mda)
@@ -1055,7 +1055,7 @@  static int apic_set_eoi(struct kvm_lapic *apic)
 		return vector;
 
 	apic_clear_isr(vector, apic);
-	apic_update_ppr(apic);
+	apic_update_ppr(apic, true);
 
 	if (test_bit(vector, vcpu_to_synic(apic->vcpu)->vec_bitmap))
 		kvm_hv_synic_send_eoi(apic->vcpu, vector);
@@ -1170,7 +1170,7 @@  static u32 __apic_read(struct kvm_lapic *apic, unsigned int offset)
 		val = apic_get_tmcct(apic);
 		break;
 	case APIC_PROCPRI:
-		apic_update_ppr(apic);
+		apic_update_ppr(apic, true);
 		val = kvm_apic_get_reg(apic, offset);
 		break;
 	case APIC_TASKPRI:
@@ -1776,7 +1776,7 @@  void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
 		kvm_lapic_set_base(vcpu,
 				vcpu->arch.apic_base | MSR_IA32_APICBASE_BSP);
 	vcpu->arch.pv_eoi.msr_val = 0;
-	apic_update_ppr(apic);
+	apic_update_ppr(apic, true);
 
 	vcpu->arch.apic_arb_prio = 0;
 	vcpu->arch.apic_attention = 0;
@@ -1897,7 +1897,7 @@  nomem:
 	return -ENOMEM;
 }
 
-int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu)
+int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu, bool make_req)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
 	int highest_irr;
@@ -1905,7 +1905,7 @@  int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu)
 	if (!apic_enabled(apic))
 		return -1;
 
-	apic_update_ppr(apic);
+	apic_update_ppr(apic, make_req);
 	highest_irr = apic_find_highest_irr(apic);
 	if ((highest_irr == -1) ||
 	    ((highest_irr & 0xF0) <= kvm_apic_get_reg(apic, APIC_PROCPRI)))
@@ -1938,9 +1938,9 @@  void kvm_inject_apic_timer_irqs(struct kvm_vcpu *vcpu)
 	}
 }
 
-int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
+int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu, bool make_req)
 {
-	int vector = kvm_apic_has_interrupt(vcpu);
+	int vector = kvm_apic_has_interrupt(vcpu, make_req);
 	struct kvm_lapic *apic = vcpu->arch.apic;
 
 	if (vector == -1)
@@ -1954,12 +1954,12 @@  int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
 	 */
 
 	apic_set_isr(vector, apic);
-	apic_update_ppr(apic);
+	apic_update_ppr(apic, true);
 	apic_clear_irr(vector, apic);
 
 	if (test_bit(vector, vcpu_to_synic(vcpu)->auto_eoi_bitmap)) {
 		apic_clear_isr(vector, apic);
-		apic_update_ppr(apic);
+		apic_update_ppr(apic, true);
 	}
 
 	return vector;
@@ -2009,7 +2009,7 @@  int kvm_apic_set_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s)
 	recalculate_apic_map(vcpu->kvm);
 	kvm_apic_set_version(vcpu);
 
-	apic_update_ppr(apic);
+	apic_update_ppr(apic, true);
 	hrtimer_cancel(&apic->lapic_timer.timer);
 	apic_update_lvtt(apic);
 	apic_manage_nmi_watchdog(apic, kvm_apic_get_reg(apic, APIC_LVT0));
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 952d02c..053d3e6 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -48,9 +48,9 @@  struct dest_map;
 int kvm_create_lapic(struct kvm_vcpu *vcpu);
 void kvm_free_lapic(struct kvm_vcpu *vcpu);
 
-int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu);
+int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu, bool make_req);
 int kvm_apic_accept_pic_intr(struct kvm_vcpu *vcpu);
-int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu);
+int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu, bool make_req);
 void kvm_apic_accept_events(struct kvm_vcpu *vcpu);
 void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event);
 u64 kvm_lapic_get_cr8(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 3d39923..7da0987 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10326,7 +10326,7 @@  static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
 
 	if ((exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
 	    && nested_exit_intr_ack_set(vcpu)) {
-		int irq = kvm_cpu_get_interrupt(vcpu);
+		int irq = kvm_cpu_get_interrupt(vcpu, true);
 		WARN_ON(irq < 0);
 		vmcs12->vm_exit_intr_info = irq |
 			INTR_INFO_VALID_MASK | INTR_TYPE_EXT_INTR;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e9c6b0c..6b547f6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6356,7 +6356,7 @@  static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
 				return r;
 		}
 		if (kvm_x86_ops->interrupt_allowed(vcpu)) {
-			kvm_queue_interrupt(vcpu, kvm_cpu_get_interrupt(vcpu),
+			kvm_queue_interrupt(vcpu, kvm_cpu_get_interrupt(vcpu, false),
 					    false);
 			kvm_x86_ops->set_irq(vcpu);
 		}