[openstack-dev] [Nova] Blueprint: standard specification of guest CPU topology

Daniel P. Berrange berrange at redhat.com
Tue Nov 19 12:15:51 UTC 2013

For attention of maintainers of Nova virt drivers

A while back there was a bug requesting the ability to set the CPU
topology (sockets/cores/threads) for guests explicitly


I countered that setting explicit topology doesn't play well with
booting images with a variety of flavours with differing vCPU counts.

This led to the following change which used an image property to
express maximum constraints on CPU topology (max-sockets/max-cores/
max-threads) which the libvirt driver will use to figure out the
actual topology (sockets/cores/threads)


I believe this is a prime example of something we must co-ordinate
across virt drivers to maximise happiness of our users.

There's a blueprint but I find the description rather hard to


So I've created a standalone wiki page which I hope describes the
idea more clearly


Launchpad doesn't let me link the URL to the blueprint since I'm not
the blurprint creator :-(

Anyway this mail is to solicit input on the proposed standard way to
express this which is hypervisor portable and the addition of some
shared code for doing the calculations which virt driver impls can
just all into rather than re-inventing

I'm looking for buy-in to the idea from the maintainers of each
virt driver that this conceptual approach works for them, before
we go merging anything with the specific impl for libvirt.

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