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: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Avi Kivity <avi@redhat.com>
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582801a95d
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@ -33,6 +33,14 @@
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static void pic_clear_isr(struct kvm_kpic_state *s, int irq)
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{
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s->isr &= ~(1 << irq);
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s->isr_ack |= (1 << irq);
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}
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void kvm_pic_clear_isr_ack(struct kvm *kvm)
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{
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struct kvm_pic *s = pic_irqchip(kvm);
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s->pics[0].isr_ack = 0xff;
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s->pics[1].isr_ack = 0xff;
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}
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/*
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@ -213,6 +221,7 @@ void kvm_pic_reset(struct kvm_kpic_state *s)
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s->irr = 0;
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s->imr = 0;
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s->isr = 0;
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s->isr_ack = 0xff;
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s->priority_add = 0;
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s->irq_base = 0;
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s->read_reg_select = 0;
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@ -444,10 +453,14 @@ static void pic_irq_request(void *opaque, int level)
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{
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struct kvm *kvm = opaque;
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struct kvm_vcpu *vcpu = kvm->vcpus[0];
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struct kvm_pic *s = pic_irqchip(kvm);
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int irq = pic_get_irq(&s->pics[0]);
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pic_irqchip(kvm)->output = level;
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if (vcpu)
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s->output = level;
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if (vcpu && level && (s->pics[0].isr_ack & (1 << irq))) {
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s->pics[0].isr_ack &= ~(1 << irq);
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kvm_vcpu_kick(vcpu);
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}
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}
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struct kvm_pic *kvm_create_pic(struct kvm *kvm)
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@ -42,6 +42,7 @@ struct kvm_kpic_state {
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u8 irr; /* interrupt request register */
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u8 imr; /* interrupt mask register */
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u8 isr; /* interrupt service register */
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u8 isr_ack; /* interrupt ack detection */
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u8 priority_add; /* highest irq priority */
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u8 irq_base;
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u8 read_reg_select;
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@ -70,6 +71,7 @@ struct kvm_pic *kvm_create_pic(struct kvm *kvm);
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void kvm_pic_set_irq(void *opaque, int irq, int level);
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int kvm_pic_read_irq(struct kvm *kvm);
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void kvm_pic_update_irq(struct kvm_pic *s);
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void kvm_pic_clear_isr_ack(struct kvm *kvm);
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static inline struct kvm_pic *pic_irqchip(struct kvm *kvm)
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{
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@ -3963,6 +3963,7 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
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pr_debug("Set back pending irq %d\n",
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pending_vec);
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}
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kvm_pic_clear_isr_ack(vcpu->kvm);
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}
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kvm_set_segment(vcpu, &sregs->cs, VCPU_SREG_CS);
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