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Commit 33e4c686 authored by Gleb Natapov's avatar Gleb Natapov Committed by Avi Kivity
Browse files

KVM: Optimize searching for highest IRR 



Most of the time IRR is empty, so instead of scanning the whole IRR on
each VM entry keep a variable that tells us if IRR is not empty. IRR
will have to be scanned twice on each IRQ delivery, but this is much
more rare than VM entry.

Signed-off-by: default avatarGleb Natapov <gleb@redhat.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 6edf14d8

arch/x86/kvm/lapic.c

+21 −3
Original line number Original line Diff line number Diff line
@@ -165,29 +165,46 @@ static int find_highest_vector(void *bitmap) 




static inline int apic_test_and_set_irr(int vec, struct kvm_lapic *apic)

static inline int apic_test_and_set_irr(int vec, struct kvm_lapic *apic)

{

{

	apic->irr_pending = true;

	return apic_test_and_set_vector(vec, apic->regs + APIC_IRR);

	return apic_test_and_set_vector(vec, apic->regs + APIC_IRR);

}

}





static inline void apic_clear_irr(int vec, struct kvm_lapic *apic)

static inline int apic_search_irr(struct kvm_lapic *apic)

{

{

	apic_clear_vector(vec, apic->regs + APIC_IRR);

	return find_highest_vector(apic->regs + APIC_IRR);

}

}





static inline int apic_find_highest_irr(struct kvm_lapic *apic)

static inline int apic_find_highest_irr(struct kvm_lapic *apic)

{

{

	int result;

	int result;





	result = find_highest_vector(apic->regs + APIC_IRR);

	if (!apic->irr_pending)

		return -1;



	result = apic_search_irr(apic);

	ASSERT(result == -1 || result >= 16);

	ASSERT(result == -1 || result >= 16);





	return result;

	return result;

}

}





static inline void apic_clear_irr(int vec, struct kvm_lapic *apic)

{

	apic->irr_pending = false;

	apic_clear_vector(vec, apic->regs + APIC_IRR);

	if (apic_search_irr(apic) != -1)

		apic->irr_pending = true;

}



int kvm_lapic_find_highest_irr(struct kvm_vcpu *vcpu)

int kvm_lapic_find_highest_irr(struct kvm_vcpu *vcpu)

{

{

	struct kvm_lapic *apic = vcpu->arch.apic;

	struct kvm_lapic *apic = vcpu->arch.apic;

	int highest_irr;

	int highest_irr;





	/* This may race with setting of irr in __apic_accept_irq() and

	 * value returned may be wrong, but kvm_vcpu_kick() in __apic_accept_irq

	 * will cause vmexit immediately and the value will be recalculated

	 * on the next vmentry.

	 */

	if (!apic)

	if (!apic)

		return 0;

		return 0;

	highest_irr = apic_find_highest_irr(apic);

	highest_irr = apic_find_highest_irr(apic);
@@ -843,6 +860,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu) 
		apic_set_reg(apic, APIC_ISR + 0x10 * i, 0);

		apic_set_reg(apic, APIC_ISR + 0x10 * i, 0);

		apic_set_reg(apic, APIC_TMR + 0x10 * i, 0);

		apic_set_reg(apic, APIC_TMR + 0x10 * i, 0);

	}

	}

	apic->irr_pending = false;

	update_divide_count(apic);

	update_divide_count(apic);

	atomic_set(&apic->lapic_timer.pending, 0);

	atomic_set(&apic->lapic_timer.pending, 0);

	if (kvm_vcpu_is_bsp(vcpu))

	if (kvm_vcpu_is_bsp(vcpu))

arch/x86/kvm/lapic.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -12,6 +12,7 @@ struct kvm_lapic { 
	struct kvm_timer lapic_timer;

	struct kvm_timer lapic_timer;

	u32 divide_count;

	u32 divide_count;

	struct kvm_vcpu *vcpu;

	struct kvm_vcpu *vcpu;

	bool irr_pending;

	struct page *regs_page;

	struct page *regs_page;

	void *regs;

	void *regs;

	gpa_t vapic_addr;

	gpa_t vapic_addr;