This sounds promising and there seems to be a feasible way to do this, but
it also sounds like a decent amount of effort and would be a new feature in
a future release rather than a bugfix - am I correct in that assessment?
On August 9, 2018 13:30:31 "Daniel P. Berrangé" <berra...@redhat.com> wrote:
On Thu, Aug 09, 2018 at 12:14:56PM -0500, Matt Riedemann wrote:
On 8/9/2018 6:03 AM, Chris Apsey wrote:
Exactly. And I agree, it seems like hw_architecture should dictate
which emulator is chosen, but as you mentioned its currently not. I'm
not sure if this is a bug and it's supposed to 'just work', or just
something that was never fully implemented (intentionally) and would be
more of a feature request/suggestion for a later version. The docs are
kind of sparse in this area.
What are your thoughts? I can open a bug if you think the scope is
reasonable.
I'm not sure if this is a bug or a feature, or if there are reasons why it's
never been done. I'm gonna have to rope in Kashyap and danpb since they'd
likely know more.
Dan/Kaskyap: tl;dr why doesn't the nova libvirt driver, configured for qemu,
set the guest.arch based on the hw_architecture image property so that you
can run ppc guests in an x86 host?
Yes, it should do exactly that IMHO !
The main caveat is that a hell of alot of code in libvirt assumes that
guest arch == host arch. ie when building guest XML there's lots of code
that looks at caps.host.cpu.arch to decide how to configure the guest.
This all needs fixing to look at the guest.arch value instead, having
set that from hw_architecture prop.
Nova libvirt driver is already reporting that it is capable of running
guest with multiple arches (the _get_instance_capaiblities method in
nova/virt/libvirt/driver.py).
The only other thing is that you likely want to distinguish between
hosts that can do PPC64 via KVM vs those that can only do it via
emulation, so you don't get guests randomly placed on slow vs fast
hosts. Some kind of scheduler filter / weighting can do that based
on info already reported from the compute host I expect.
Regards,
Daniel
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