Open Stack

We have use cases in our cloud which require vCPU-to-NUMA_node pinning
to maximise the CPU performance available in the guests. From what we’ve
seen, there was no further improvement when the vCPUs were mapped
one-to-one to pCPUs (we did not study this in detail, though, as with the
NUMA node pinning the performance was sufficiently close to the physical
one).

To implement this, we specify the numa_nodes extra_spec for the corresponding
flavor and rely on nova’s placement policy.

HTH,
 Arne

—
Arne Wiebalck
CERN IT



> On 08 Jul 2016, at 19:22, Steve Gordon <sgordon at redhat.com> wrote:
> 
> ----- Original Message -----
>> From: "Brent Troge" <brenttroge2016 at gmail.com <mailto:brenttroge2016 at gmail.com>>
>> To: openstack at lists.openstack.org <mailto:openstack at lists.openstack.org>
>> Sent: Friday, July 8, 2016 9:59:58 AM
>> Subject: [Openstack] vCPU -> pCPU MAPPING
>> 
>> context - high performance private cloud with cpu pinning
>> 
>> Is it possible to map vCPUs to specific pCPUs ?
>> Currently I see you can only direct which vCPUs are mapped to a specific
>> NUMA node
>> 
>> hw:numa_cpus.0=1,2,3,4
> 
> Just in addition to Jay's comment, the above does not do what I suspect you think it does. The above tells Nova to expose vCPUs 1, 2, 3, and 4 in *guest* NUMA node 0 when building the guest NUMA topology in the Libvirt XML. Nova will endeavor to map these vCPUs to pCPUs on the same NUMA node on the host as *each other* but that will not necessarily be NUMA node *0* on the host depending on resource availability.
> 
> Thanks,
> 
> Steve
> 
>> However, to get even more granular, is it possible to create a flavor which
>> maps vCPU to specific pCPU within a numa node ?
>> 
>> Something like:
>> hw:numa_cpus.<NUMA-NODE>-<pCPU>=<vCPU>
>> 
>> hw:numa_cpus.0-1=1
>> hw:numa_cpus.0-2=2
>> 
>> 
>> Thanks!
>> 
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