libvirt: number of CPUs is not updated after hotplugging host CPUs

[Alexander Schmidt]

When adding or removing CPUs to a compute node running the libvirt driver, the correct new amount of CPUs is not reported to the controller/scheduler.

As a result, the scheduler will not consider added or removed capacity in future scheduling decisions.

To fix this, the number of CPUs on a compute node should not be cached in the libvirt driver. Instead it should be recalculated in the periodic task for updating resource availability.

I'll provide a patch for fixing the bug along with a unit test.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/186746

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/186746
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=d6741a03c0b934083afcd2b4345354c86623783f
Submitter: Jenkins
Branch: master

commit d6741a03c0b934083afcd2b4345354c86623783f
Author: Alexander Schmidt <email address hidden>
Date: Fri May 29 11:42:02 2015 +0200

    libvirt: Do not cache number of CPUs of the hypervisor

    The number of CPUs on a compute node can vary during the runtime of
    the nova compute service due to CPU hotplug events. For example
    an administrator can add or remove CPUs based on the current
    resource consumption.

    As a result, the number of CPUs should not be cached within
    the nova service, but it needs to be retrieved again when
    updating resource allocation to report it to the controller
    node.

    Change-Id: I2382a22c7aa492071647fa6dca42b54d1baf050d
    Closes-bug: #1460043