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[nova] NUMA scheduling


What is the error thrown by Openstack when NUMA0 is full?

On Sat, Oct 17, 2020 at 11:40 AM Eric K. Miller <emiller at genesishosting.com>
wrote:

> Hi Satish,
>
> > This is very odd, I am running NUMA aware openstack cloud and my VMs
> > are getting scheduled on both sides of NUMA zone. Following is my
> > flavor settings. Also I am using huge pages for performance. (make
> > sure you have NUMATopologyFilter filter configured).
> >
> > hw:cpu_policy='dedicated', hw:cpu_sockets='2', hw:cpu_threads='2',
> > hw:mem_page_size='large'
> >
> > what if you remove hw:numa_nodes=1 ?
>
> Note that we are using a shared CPU policy (for various hosts).  I don't
> know if this is causing our issue or not, but we definitely do not want to
> pin CPUs to VMs on these hosts.
>
> Without the hw:numa_nodes property, an individual VM is created with its
> vCPUs and Memory divided between the two NUMA nodes, which is not what we
> would prefer.  We would prefer, instead, to have all vCPUs and Memory for
> the VM placed into a single NUMA node so all cores of the VM have access to
> this NUMA node's memory instead of having one core require cross-NUMA
> communications.
>
> With large core processors and large amounts of memory, it doesn't make
> much sense to have small VMs (such as 4 core VMs) span two NUMA nodes.
>
> With our current settings, every VM is placed into a single NUMA node (as
> we wanted), but they always land in NUMA node 0 and never in NUMA node 1.
> It does, however, appear that QEMU's memory overhead and Linux'
> buffer/cache is landing in NUMA node 1.  Native processes on the hosts are
> spread between NUMA nodes.
>
> We don't have huge pages enabled, so we have not enabled the
> NUMATopologyFilter.
>
> Eric
>
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