Re: KVM: PIC: enhance IPI avoidance

[Avi Kivity <avi@redhat.com>]

Marcelo Tosatti wrote:
> 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>
>
>  struct kvm_pic *kvm_create_pic(struct kvm *kvm)
> Index: kvm/arch/x86/kvm/irq.h
> ===================================================================
> --- kvm.orig/arch/x86/kvm/irq.h
> +++ kvm/arch/x86/kvm/irq.h
> @@ -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;
>   

Needs to be cleared by reset and by register load from userspace, no?

-- 
error compiling committee.c: too many arguments to function