[openstack-dev] [nova] Stein PTG summary

Eric Fried openstack at fried.cc
Thu Sep 27 15:15:11 UTC 2018

On 09/27/2018 07:37 AM, Matt Riedemann wrote:
> On 9/27/2018 5:23 AM, Sylvain Bauza wrote:
>> On Thu, Sep 27, 2018 at 2:46 AM Matt Riedemann <mriedemos at gmail.com
>> <mailto:mriedemos at gmail.com>> wrote:
>>     On 9/26/2018 5:30 PM, Sylvain Bauza wrote:
>>      > So, during this day, we also discussed about NUMA affinity and we
>>     said
>>      > that we could possibly use nested resource providers for NUMA
>>     cells in
>>      > Stein, but given we don't have yet a specific Placement API
>>     query, NUMA
>>      > affinity should still be using the NUMATopologyFilter.
>>      > That said, when looking about how to use this filter for vGPUs,
>>     it looks
>>      > to me that I'd need to provide a new version for the NUMACell
>>     object and
>>      > modify the virt.hardware module. Are we also accepting this
>>     (given it's
>>      > a temporary question), or should we need to wait for the
>>     Placement API
>>      > support ?
>>      >
>>      > Folks, what are you thoughts ?
>>     I'm pretty sure we've said several times already that modeling
>> NUMA in
>>     Placement is not something for which we're holding up the extraction.
>> It's not an extraction question. Just about knowing whether the Nova
>> folks would accept us to modify some o.vo object and module just for a
>> temporary time until Placement API has some new query parameter.
>> Whether Placement is extracted or not isn't really the problem, it's
>> more about the time it will take for this query parameter ("numbered
>> request groups to be in the same subtree") to be implemented in the
>> Placement API.
>> The real problem we have with vGPUs is that if we don't have NUMA
>> affinity, the performance would be around 10% less for vGPUs (if the
>> pGPU isn't on the same NUMA cell than the pCPU). Not sure large
>> operators would accept that :(
>> -Sylvain
> I don't know how close we are to having whatever we need for modeling
> NUMA in the placement API, but I'll go out on a limb and assume we're
> not close.

True story. We've been talking about ways to do this since (at least)
the Queens PTG, but haven't even landed on a decent design, let alone
talked about getting it specced, prioritized, and implemented. Since
full NRP support was going to be a prerequisite in any case, and our
Stein plate is full, Train is the earliest we could reasonably expect to
get the placement support going, let alone the nova side. So yeah...

> Given that, if we have to do something within nova for NUMA
> affinity for vGPUs for the NUMATopologyFilter, then I'd be OK with that
> since it's short term like you said (although our "short term"
> workarounds tend to last for many releases). Anyone that cares about
> NUMA today already has to enable the scheduler filter anyway.

+1 to this ^


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