Re: Re: [libvirt PATCH 3/5] Config some capabilities for loongarch virt machine
On Tue, Dec 19, 2023 at 11:52:03AM +0800, lixianglai wrote:
> So does loongarch actually have ioapic support? Just making
sure. I'm
> surprised because apparently no other non-x86 architecture supports
> it...
Yes, loongarch does have IOAPIC, but this feature has no effect on loongarch
at this stage, I will cut it first to simplify the committed code.
In addition, I have a question, if I understand correctly, the IOAPIC here
should be the device interrupt controller, which is located in the bridge
chip,
it is called IOAPIC under x86, PCH_PIC under loongarch, and GIC under arm.
The kernel_irqchip attribute of the machine parameter in qemu corresponding
to the function VIR_DOMAIN_FEATURE_IOAPIC determines
whether the device interrupt controller is simulated in qemu or kvm. So arm
also has such a need, but why doesn't arm add?
Okay, so x86's IOAPIC is controlled by the <ioapic> element, while
Arm's GIC uses the <gic> element. By that logic, loongarch should
probably introduce a <phc-pic> element.
It's a bit silly that we need a separate element per architecture,
especially considering that most of the time we just want to control
the kernel_irqchip flag. Case in point, as you noticed Arm doesn't
expose the ability to configure that at the moment.
On the other hand, additional arch-features might show up in the
future, at which point the separate element would start making sense.
See GIC for an example.
Overall, if you don't have a pressing need to expose the ability to
control the kernel_irqchip flag I would just avoid doing anything
about it now and leave the decision for another day and, possibly,
person :)
--
Andrea Bolognani / Red Hat / Virtualization