Re: [Qemu-devel] [PATCH] kvm: Move kvm_allows_irq0_override() to target-i386

[Peter Maydell]

On 23 July 2012 13:26, Avi Kivity <address@hidden> wrote:
> Really, "irqchip in kernel" means asynchronous interrupts - you can
> inject an interrupt from outside the vcpu thread.  Obviously if the vcpu
> is sleeping you need to wake it up and that pulls in idle management.
>
> "irqchip" for x86 really means the local APIC, which has a synchronous
> interface with the cpu core.  "local APIC in kernel" really is
> equivalent to "kernel idle management", "KVM_IRQ_LINE", and irqfd.  The
> ioapic and pit, on the other hand, don't contribute anything to this
> (just performance).

> So yes, ARM with and without GIC are irqchip_in_kernel, since the
> ARM<->GIC interface is asynchronous.  Whether to emulate the GIC or not
> is just a performance question.

So should we be using something other than KVM_CREATE_IRQCHIP to
ask the kernel to create a GIC model for us (and leave KVM_CREATE_IRQCHIP
as a dummy "always succeed" ioctl)?

> So my view is that ARM with and without kernel GIC are
> irqchip_in_kernel, since whatever is the local APIC in ARM is always
> emulated in the kernel.

I'm not sure ARM has any equivalent to the local APIC -- the GIC
deals with everything and we don't have any equivalent division
of labour to the x86 LAPIC-IOAPIC one.

-- PMM