Only CPU compute monitors are loaded by compute.monitors extension loader

[Jay Pipes]

There is a TODO in the extension loader for compute monitors:

        # TODO(jaypipes): Right now, we only have CPU monitors, so we don't
        # need to check if the plugin is a CPU monitor or not. Once non-CPU
        # monitors are added, change this to check either the base class or
        # the set of metric names returned to ensure only a single CPU
        # monitor is loaded at any one time.

We need a mechanism to load other types of compute monitors than CPU.

[Sylvain Bauza (sylvain-bauza)]

Sorry, tagging as wishlist, that's not technically a bug, something is not broken or in regression, right?

[Matt Riedemann (mriedem)]

I think it's OK to call this wishlist.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/209499
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=c250aca00ba89b6fad86bfaebb3083e9f5c55f3b
Submitter: Jenkins
Branch: master

commit c250aca00ba89b6fad86bfaebb3083e9f5c55f3b
Author: Jay Pipes <email address hidden>
Date: Wed Aug 5 08:49:26 2015 -0400

    Allow compute monitors in different namespaces

    The code recently added to clean up the compute monitor loading to use
    stevedore was assuming a single type of compute monitor: cpu monitors.
    This patch allows multiple monitor types, namespaced by the directory in
    nova/compute/monitors. The NUMA memory bandwidth monitor is the next
    monitor namespace to be proposed, and this code sets up that patch
    series.

    DocImpact: This patch provides the infrastructure for non-CPU compute
    monitors to be loaded properly by the stevedore extension manager. The
    CONF.compute_monitors configuration option previously supported only CPU
    monitors, and so the format of the configuration option (which is a
    multi-list option) looked like this: CONF.compute_monitors = ['virt_driver'],
    which could be read as "Use the virt_driver CPU monitor". Now, non-CPU
    monitors can be loaded by the extension manager, and so a namespace
    prefix is also considered. For example, setting CPU.compute_monitors to
    ['cpu.virt_driver', 'numa_mem_bw.virt_driver'] would allow the loading
    of both the virt_driver CPU monitor and the virt_driver NUMA memory
    bandwidth monitor. To preserve backwards compatibility, if there is no
    namespace given, the 'cpu.' namespace is assumed.

    Closes-bug: 1487070
    Change-Id: I7ad45d5c5d617625b76cc79a65f8c185a24c79b6