[placement][nova][ptg] Summary: Nested Magic With Placement
cdent+os at anticdent.org
Fri May 3 18:22:45 UTC 2019
This message is an attempt to summarize some of the discussions held
yesterday during the nova-placement cross project session  that
were in some way related to the handling of nested providers. There
were several individual topics:
* NUMA Topology with placement
* Subtree affinity with placement
* Request group mapping
* Resourceless trait filters
But they are all closely inter-related, so summarizing the
discussion here as a lump.
There was some discussion raised about whether representing NUMA
topology in placement was worth pursuing as it is not strictly
necessary and dang it is sure taking us a long time to get there
and will replace an existing set of worms with a new set of worms.
The conversation to resolved to: It's worth trying.
To make it work there are some adjustments required to how placement
* We need to implement a form of the can_split feature (as
previously described in ) to allow some classes of resource to
be satisfied by multiple providers.
* The `group_policy=same_tree[...]` concept is needed (as initially
proposed in ) for affinity (and anti). Some discussion on
implementation has started at  and there will be in-person
discussion in the placement PTG room tomorrow (Saturday)
* trait and aggregate membership should "flow down" when making any
kind of request (numbered or unnumbered). This is closely tied to
the implementation of the previous point.
* Being able to express 'required' without a 'resources' is
required when making an allocation candidates query.
* There are several in-flight nova patches where some hacks to
flavors are being performed to work around the current lack of
this feature. These are okay and safe to carry on with because
they are ephemeral.
* The number required and resources query parameters need to accept
arbitrary strings so it is possible to say things like
'resources_compute' and 'resources_network' to allow conventions
to emerge when multiple parties may be involved in manipulating a
* A 'mappings' key will be added to the 'allocations' object in the
allocation_candidates response that will support request group
* There will be further discussion on these features Saturday at the
PTG starting at 13:30.
* This (Friday) afternoon at the PTG I'll be creating rfe stories
associated with these changes. If you'd like to help with that, find
me in the placement room (109). We'll work out whether those
stories needs specs in the normally processing of the stories.
We'll also need to find owners for many of them.
* Gibi will be updating the request group mapping spec.
Chris Dent ٩◔̯◔۶ https://anticdent.org/
freenode: cdent tw: @anticdent
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