Re: [RFC PATCH 4/5] APIC/IOAPIC EOI callback

Avi Kivity
2010-07-11T18:31:05Z

On 07/11/2010 09:26 PM, Alex Williamson wrote:
> On Sun, 2010-07-11 at 21:14 +0300, Avi Kivity wrote:
>
>> On 07/11/2010 09:09 PM, Alex Williamson wrote:
>>
>>> For device assignment, we need to know when the VM writes an end
>>> of interrupt to the APIC, which allows us to de-assert the interrupt
>>> line and clear the DisINTx bit. Add a new wrapper for ioapic
>>> generated interrupts with a callback on eoi and create an interface
>>> for drivers to be notified on eoi.
>>>
>>>
>> You aren't going to get this with kvm's in-kernel irqchip, so we need a
>> new interface there.
>>
> Registering an eventfd for the eoi seems like a reasonable alternative.
>

I'm worried about that racing (with what?)

> I also need to figure out how to avoid bouncing the vfio interrupt
> events through qemu, but it's a functional start. Thanks,
>

I thought the scheduler has/wants to have something that moves the irq
to whatever thread it wakes up. With irqfd, it would flow naturally.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.