Re: [Qemu-devel] live migration vs device assignment (motivation)

[Michael S. Tsirkin]

On Mon, Dec 28, 2015 at 11:52:43AM +0300, Pavel Fedin wrote:
>  Hello!
> 
> > A dedicated IRQ per device for something that is a system wide event
> > sounds like a waste.  I don't understand why a spec change is strictly
> > required, we only need to support this with the specific virtual bridge
> > used by QEMU, so I think that a vendor specific capability will do.
> > Once this works well in the field, a PCI spec ECN might make sense
> > to standardise the capability.
> 
>  Keeping track of your discussion for some time, decided to jump in...
>  So far, we want to have some kind of mailbox to notify the quest about 
> migration. So what about some dedicated "pci device" for
> this purpose? Some kind of "migration controller". This is:
> a) perhaps easier to implement than capability, we don't need to push 
> anything to PCI spec.
> b) could easily make friendship with Windows, because this means that no bus 
> code has to be touched at all. It would rely only on
> drivers' ability to communicate with each other (i guess it should be 
> possible in Windows, isn't it?)
> c) does not need to steal resources (BARs, IRQs, etc) from the actual devices.
> 
> Kind regards,
> Pavel Fedin
> Expert Engineer
> Samsung Electronics Research center Russia
> 

Sure, or we can use an ACPI device.  It doesn't really matter what we do
for the mailbox. Whoever writes this first will get to select a
mechanism.

-- 
MST