device compatibility interface for live migration with assigned devices

[Daniel P. Berrangé]

On Tue, Jul 14, 2020 at 02:47:15PM -0600, Alex Williamson wrote:
> On Tue, 14 Jul 2020 17:47:22 +0100
> Daniel P. Berrangé <berrange at redhat.com> wrote:

> > I'm sure OpenStack maintainers can speak to this more, as they've put
> > alot of work into their scheduling engine to optimize the way it places
> > VMs largely driven from simple structured data reported from hosts.
> 
> I think we've weeded out that our intended approach is not worthwhile,
> testing a compatibility string at a device is too much overhead, we
> need to provide enough information to the management engine to predict
> the response without interaction beyond the initial capability probing.

Just to clarify in case people mis-interpreted my POV...

I think that testing a compatibility string at a device *is* useful, as
it allows for a final accurate safety check to be performed before the
migration stream starts. Libvirt could use that reasonably easily I
believe.

It just isn't sufficient for a complete solution.

In parallel with the device level test in sysfs, we need something else
to support the host placement selection problems in an efficient way, as
you are trying to address in the remainder of your mail.


Regards,
Daniel
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