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#openstack-nova - 2018-04-12
15:32:34 efried cfriesen: But IIUC, filters like NUMATopologyFilter are opt-in, and have a predefined interface (so folks can create custom ones), and only let you say "this host is good or bad".
15:32:40 cfriesen efried: to me the scheduler is placement+filters+weighers
15:33:18 efried cfriesen: I'm saying what we need here to make the world sane is a piece of code that "filters" allocation requests out of the result of GET /allocation_candidates.
15:33:56 efried cfriesen: In order for that code to be in a "filter" (as described above), we would have to extend/reinvent that predefined interface.
15:34:16 efried cfriesen: But if we do that filtering outside of that interface, we're not restricted.
15:34:35 efried cfriesen: Somewhere in the scheduler there is a piece of code that looks at the list of allocation requests we get back from placement, and picks one.
15:34:37 efried (or three)
15:35:32 openstackgerrit Matt Riedemann proposed openstack/nova stable/queens: Don't persist RequestSpec.retry https://review.openstack.org/560143
15:35:39 efried cfriesen: We need to get our dirty hands into that algorithm in order to satisfy this use case - unless we can find a way for the filtering to be done 100% in placement.
15:37:50 edleafe efried: I really don't like any approach that doesn't treat allocation_candidates as opaque
15:38:22 efried edleafe: Brace yourself. It's going to happen eventually. If not for this, then for something.
15:38:37 cfriesen efried: looks like SchedulerManager.select_destinations() calls out to placement, then passes the returned information down to FilterScheduler.select_destinations()
15:38:46 efried edleafe: Because we can't expect to implement *all* weighing on the placement side.
15:39:05 efried cfriesen: Is a "destination" a host in that context?
15:39:20 efried (trying not to look at code; have a pile of reviews I'm already in the middle of)
15:39:48 cfriesen efried: yes. Looks like when we call down to the actual filters (via _get_sorted_hosts() in this case, we don't pass the allocation candidates)
15:39:51 edleafe efried: it doesn't have to happen
15:40:29 edleafe I really oppose making the internal structure of an a-c part of the API contract
15:43:59 efried edleafe: /me predicts that that will be the path of least resistance when the alternative is implementing every conceivable filtering/weighing algorithm natively in placement.
15:44:06 cfriesen edleafe: I can see what efried is saying though...placement is returning allocation candidates, not hosts. Something in the rest of the code needs to understand how to map that allocation candidate to the actual resources being used.
15:44:46 efried cfriesen: That's slightly different. The format of the *allocation* is part of the contract, and the virt driver (or whatever) can introspect it to map to actual resources.
15:44:56 gameon sahid: Thanks again for your help - I have resolved the issue. It turns out Broadwell doesn't have all Haswell features and vice versa. So I've used IvyBridge
15:45:27 efried cfriesen: Although it amounts to the same thing, really.
15:45:35 cfriesen gameon: what was in haswell that's not in broadwell?
15:45:38 efried cfriesen: So yeah, edleafe there's your counterargument.
15:46:16 sahid gameon: cool :)
15:47:31 edleafe efried: I would much prefer modifying the provider info than the a-c
15:47:58 efried edleafe: But our problem isn't picking a provider. It's picking an allocation request.
15:48:07 gameon cfriesen: this was generated by running virsh capabilities - I the features reported by 'cat /proc/cpuinfo' are the same... http://paste.openstack.org/show/719064/
15:48:18 efried edleafe: ...from among possibly many for a given provider.
15:48:41 efried edleafe: Besides, we're not talking about modifying anything about the format of the response.
15:48:48 gameon cfriesen: happy to hear alternative solutions to setting model to IvyBridge there's a better way of allowing LM between these set of hosts
15:49:23 efried edleafe: But we are talking about introspecting that payload. Which nothing in the doc implies we should avoid...
15:49:50 edleafe efried: but it also doesn't guarantee that the payload structure will never change
15:50:07 edleafe "Introspect at your own risk" :)
15:50:31 cfriesen gameon: according to my libvirt cpu model definitions Broadwell should be a superset of Haswell.
15:50:46 bauzas edleafe: just a bit of explanation
15:50:48 cfriesen gameon: and you might want to use the "noTSX" versions
15:51:09 bauzas edleafe: we discussed since 3 hours with efried about the possible implementation for NUMA
15:51:19 openstackgerrit Matt Riedemann proposed openstack/nova stable/pike: Don't persist RequestSpec.retry https://review.openstack.org/560146
15:51:32 bauzas edleafe: the problem is that the NUMA filter makes some assumptions that are not supported by the numbered request groups feature
15:51:48 gameon cfriesen: I'll give it a go, let's see. So set it to Broadwell or Haswell do you think?
15:51:58 bauzas edleafe: the one in particular is that it checks whether the host has the exact same topology than the asked guest one
15:52:07 bauzas edleafe: which seems weird to me, but meh
15:52:44 cfriesen gameon: interesting that it doesn't report your Haswell as a Haswell.
15:52:52 bauzas edleafe: accordingly, that means that placement will return some allocation requests that are valid from his point of view, but not from the filter's PoV
15:53:17 bauzas edleafe: hence the need of some post-filtering that would only assure the same behaviour
15:53:20 bauzas but
15:53:21 gameon cfriesen: Yes I noticed this, reported as Nehalem which is a bit puzzling...
15:53:23 bauzas there is a but
15:53:25 cfriesen gameon: According to what you've got there I'd use Nehalem, unless you need the newer features.
15:53:57 bauzas edleafe: one other option could be to consider that placement should return the exact same candidates as the ones that the filter would agree
15:54:10 bauzas edleafe: in that case, it would mean some new query param for Placement
15:54:21 bauzas thoughts ?
15:55:05 gameon cfriesen: Nehalem works :)
15:56:27 efried edleafe: The way the doc is written, it *is* guaranteeing that the format won't change (without a new microversion).
15:56:53 efried which is as it should be.
15:57:10 edleafe efried: about to run off to a meeting
15:57:17 efried I've never understood the reasoning behind that payload needing to be opaque, btw.
15:57:50 edleafe efried: all it was supposed to be was something you could send back to allocate/claim
15:57:53 cfriesen bauzas: it seems to me that we have two options. give the filters access to the allocation candidates so they can rule out ones they don't like, or have enough flexibility in placement that we can ensure we never get back invalid candidates.
15:58:03 edleafe it could have been a hash, or a uuid, or...
15:58:22 efried edleafe: And you're supposed to pick one based on... what?
15:58:32 cfriesen edleafe: for that to work we need enough flexibility in what we can request from placement to ensure that all the candidates are valid
15:58:33 edleafe now we have nested, which brings in multiple a-cs per rp
15:58:35 melwitt efried: when you get a chance, wanna write some notes on how the update-provider-tree runway review went at L118? https://etherpad.openstack.org/p/nova-runways-rocky
15:58:47 efried melwitt: ack
15:58:51 edleafe efried: you picked a host, and found the matching a-c
15:59:08 efried edleafe: There were several a-cs for that host.
15:59:13 efried edleafe: How did I pick one?
15:59:19 edleafe now there isn't a 1:1 host:a-c relationship with nesting
15:59:22 cfriesen efried: if they were all actually valid it wouldn't matter
15:59:37 efried cfriesen: Yup, that's the big IF.
16:00:05 efried cfriesen: For this use case, we either implement new logic in placement, or they're *not* all valid and we can't just pick one at random.
16:00:14 cfriesen efried: yes, agreed
16:00:43 efried edleafe: There was never a 1:1 host:a-c relationship.
16:05:01 openstackgerrit Matt Riedemann proposed openstack/nova stable/ocata: Don't persist RequestSpec.retry https://review.openstack.org/560955
16:06:24 bauzas efried: just for the context, they're not all valid because of some specific implementation details of the filter that I don't particularly like
16:06:53 efried melwitt: done
16:06:58 bauzas adding more debt to either placement or the filters looks terrible to me
16:07:06 openstackgerrit Matt Riedemann proposed openstack/nova stable/ocata: Don't persist RequestSpec.retry https://review.openstack.org/560167
16:07:18 melwitt efried: thanks
16:07:45 bauzas efried: from a placement perspective, we can ask for a query that would *shard* resources between children, but that's the only trade-off I'd make
16:08:18 bauzas efried: if we implement such thing, then we wouldn't need to pass the candidates down to the filters
16:08:22 efried bauzas: It's starting to sound like that might be the "easier" option
16:08:37 bauzas not the easier
16:08:43 efried bauzas: And as I've said, we know we're going to want that logic in placement eventually regardless.
16:08:46 bauzas the less debtful
16:08:49 efried bauzas: So this might as well be the motivation.
16:08:51 efried Yeah
16:09:19 bauzas ok, I'll amend my spec accordingly
16:09:27 edleafe efried: sorry, in the API-SIG meeting
16:09:30 edleafe efried: https://github.com/openstack/nova/blob/master/nova/scheduler/manager.py#L154-L160
16:09:49 edleafe That creates one a-c per rp
16:10:00 melwitt cdent: the placement-forbidden-traits blueprint has been added to a review runway. please ack if the next two weeks work for you for quick iteration on review
16:10:25 edleafe we always just grab the first one of that list
16:11:13 cdent melwitt: thanks, it does
16:11:24 melwitt k, great
16:11:28 efried edleafe: It creates a *list* of allocation requests per rp_uuid
16:11:44 efried edleafe: ...by introspecting the payload, by the way :P

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