Commit e4825800 authored by Marcelo Tosatti's avatar Marcelo Tosatti Committed by Avi Kivity
Browse files

KVM: PIC: enhance IPI avoidance 



The PIC code makes little effort to avoid kvm_vcpu_kick(), resulting in
unnecessary guest exits in some conditions.

For example, if the timer interrupt is routed through the IOAPIC, IRR
for IRQ 0 will get set but not cleared, since the APIC is handling the
acks.

This means that everytime an interrupt < 16 is triggered, the priority
logic will find IRQ0 pending and send an IPI to vcpu0 (in case IRQ0 is
not masked, which is Linux's case).

Introduce a new variable isr_ack to represent the IRQ's for which the
guest has been signalled / cleared the ISR. Use it to avoid more than
one IPI per trigger-ack cycle, in addition to the avoidance when ISR is
set in get_priority().

Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 582801a9

arch/x86/kvm/i8259.c

+15 −2
Original line number Diff line number Diff line
@@ -33,6 +33,14 @@ 
static void pic_clear_isr(struct kvm_kpic_state *s, int irq)

{

	s->isr &= ~(1 << irq);

	s->isr_ack |= (1 << irq);

}



void kvm_pic_clear_isr_ack(struct kvm *kvm)

{

	struct kvm_pic *s = pic_irqchip(kvm);

	s->pics[0].isr_ack = 0xff;

	s->pics[1].isr_ack = 0xff;

}



/*
@@ -213,6 +221,7 @@ void kvm_pic_reset(struct kvm_kpic_state *s) 
	s->irr = 0;

	s->imr = 0;

	s->isr = 0;

	s->isr_ack = 0xff;

	s->priority_add = 0;

	s->irq_base = 0;

	s->read_reg_select = 0;
@@ -444,11 +453,15 @@ static void pic_irq_request(void *opaque, int level) 
{

	struct kvm *kvm = opaque;

	struct kvm_vcpu *vcpu = kvm->vcpus[0];

	struct kvm_pic *s = pic_irqchip(kvm);

	int irq = pic_get_irq(&s->pics[0]);



	pic_irqchip(kvm)->output = level;

	if (vcpu)

	s->output = level;

	if (vcpu && level && (s->pics[0].isr_ack & (1 << irq))) {

		s->pics[0].isr_ack &= ~(1 << irq);

		kvm_vcpu_kick(vcpu);

	}

}



struct kvm_pic *kvm_create_pic(struct kvm *kvm)

{

arch/x86/kvm/irq.h

+2 −0
Original line number Diff line number Diff line
@@ -42,6 +42,7 @@ struct kvm_kpic_state { 
	u8 irr;		/* interrupt request register */

	u8 imr;		/* interrupt mask register */

	u8 isr;		/* interrupt service register */

	u8 isr_ack;	/* interrupt ack detection */

	u8 priority_add;	/* highest irq priority */

	u8 irq_base;

	u8 read_reg_select;
@@ -70,6 +71,7 @@ struct kvm_pic *kvm_create_pic(struct kvm *kvm); 
void kvm_pic_set_irq(void *opaque, int irq, int level);

int kvm_pic_read_irq(struct kvm *kvm);

void kvm_pic_update_irq(struct kvm_pic *s);

void kvm_pic_clear_isr_ack(struct kvm *kvm);



static inline struct kvm_pic *pic_irqchip(struct kvm *kvm)

{

arch/x86/kvm/x86.c

+1 −0
Original line number Diff line number Diff line
@@ -3963,6 +3963,7 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu, 
			pr_debug("Set back pending irq %d\n",

				 pending_vec);

		}

		kvm_pic_clear_isr_ack(vcpu->kvm);

	}



	kvm_set_segment(vcpu, &sregs->cs, VCPU_SREG_CS);

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