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


From: Avi Kivity
Subject: [Qemu-devel] Re: [RFC PATCH 4/5] APIC/IOAPIC EOI callback
Date: Sun, 11 Jul 2010 21:30:59 +0300
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.10) Gecko/20100621 Fedora/3.0.5-1.fc13 Thunderbird/3.0.5

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.




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