Comment 0 for bug 1466780

Using a CPU policy of dedicated ('hw:cpu_policy=dedicated') results in vCPUs being pinned to pCPUs, per the original blueprint:

    http://specs.openstack.org/openstack/nova-specs/specs/kilo/implemented/virt-driver-cpu-pinning.html

When scheduling instance with this extra spec, it would be expected that the 'VirtCPUToplogy' object used by 'InstanceNumaCell' objects (which are in turn used by an 'InstanceNumaTopology' object) should bear some reflection on the actual configuration. For example, a VM booted with four vCPUs and the 'dedicated' CPU policy should have NUMA topologies similar to one of the below:

    VirtCPUTopology(cores=4,sockets=1,threads=1)
    VirtCPUTopology(cores=2,sockets=1,threads=2)
    VirtCPUTopology(cores=1,sockets=2,threads=2)
    ...

In summary, cores * sockets * threads = vCPUs. However, this does not appear to happen.

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# Testing Configuration

Testing was conducted on a single-node, Fedora 21-based (3.17.8-300.fc21.x86_64) OpenStack instance (built with devstack). The system is a dual-socket, 10 core, HT-enabled system (2 sockets * 10 cores * 2 threads = 40 "pCPUs". 0-9,20-29 = node0, 10-19,30-39 = node1). Two flavors were used:

    openstack flavor create --ram 4096 --disk 20 --vcpus 10 demo.no-pinning

    openstack flavor create --ram 4096 --disk 20 --vcpus 10 demo.pinning
    nova flavor-key demo.pinning set hw:cpu_policy=dedicated hw:cpu_threads_policy=separate

# Results

Results vary - however, we have seen very random assignments like so:

For a three vCPU instance:

    (Pdb) p instance.numa_topology.cells[0].cpu_topology
    VirtCPUTopology(cores=10,sockets=1,threads=1)

For a four vCPU instance:

    VirtCPUTopology(cores=2,sockets=1,threads=2)

For a ten vCPU instance:

    VirtCPUTopology(cores=7,sockets=1,threads=2)

The actual underlying libvirt XML is correct, however:

For example, for a three vCPU instance:

    <cputune>
        <shares>3072</shares>
        <vcpupin vcp='0' cpuset='1'/>
        <vcpupin vcp='1' cpuset='0'/>
        <vcpupin vcp='2' cpuset='25'/>
    </cputune>