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#openstack-nova - 2018-03-14
17:25:51 sean-k-mooney jaypipes: proably i am just skimming the scoll back now
17:26:00 cdent cfriesen: ah, sorry, I had misunderstood which "we" you meant :)
17:26:07 sean-k-mooney i was in meeting all day up until this point
17:27:02 jaypipes cfriesen: a single nova boot request is only handled by a single worker, no? the case you're worrying about is multiple clients calling nova boot with the same server group.
17:27:44 jaypipes cfriesen: as for the NUMA issues, I don't think that changing to multiple workers will make a difference in the number of retries that happen.
17:27:59 sean-k-mooney jaypipes: or perhaps the nova multi boot support we you say boot x instance of y flavour on network z ?
17:28:22 jaypipes sean-k-mooney: I don't understand how that's relevant?
17:28:39 jaypipes sean-k-mooney: that would be handled in a single thread.
17:29:04 jaypipes sean-k-mooney: the only situation cfriesen is worried about is when multiple nova boot requests involving the same server group were executed simultaneously.
17:29:12 sean-k-mooney jaypipes: i was wondering if that was a single boot request form the api point of view or x independet ones and a client feature
17:29:35 jaypipes sean-k-mooney: a single nova boot is a single thread of execution.
17:30:47 sean-k-mooney jaypipes: ya that makes sense. and nova boot --min 3 --max 3 --server-group... is considered a singel boot request
17:31:32 sean-k-mooney jaypipes: so the only race would be if two client tried to boot servers in the same group concureently without the server group already having running instances
17:32:17 jaypipes sean-k-mooney: yes, that is considered a single boot request.
17:33:51 jaypipes sean-k-mooney: almost. the only race is two clients concurrently attempting to add instances to the same server group (regardless of whether the server group has members). and that is a situation I find pretty rare and not worth shooting the rest of the world in the foot for.
17:35:26 cfriesen jaypipes: the scenario I'm worried about is where two instances race to schedule and get put onto the same compute node, but then one of them claims a mix of resources that causes the other to fail it's resource allocation. With a single sched worker this is less likely (though still possible).
17:35:57 jaypipes cfriesen: unless those are NUMA resources, it's not possible to do that.
17:36:01 mriedem arvindn05: ok what's up
17:36:21 cfriesen jaypipes: yes, numa resources. CPUs, hugepages, PCI devices with strict affinity
17:37:22 mriedem arvindn05: oh i'll read your replies
17:37:37 cfriesen I'm totally fine with the change to enable multiple workers, I just thing we might want to mention in the release notes that it could increase races in some cases.
17:39:17 bauzas jaypipes: cfriesen: I'm totally up for deprecating https://developer.openstack.org/api-ref/compute/#create-multiple-servers y'know
17:39:28 melwitt mriedem: on this bp, when you say you'd like to see the proposed code for deleting a server, did you mean you want to wait for proposed code before approving the bp? https://blueprints.launchpad.net/nova/+spec/add-server-group-remove-member-notifications
17:39:31 bauzas it creates more problems than it solves
17:39:56 cfriesen jaypipes: for server groups there's also the case where you resize/migrate/evacuate instances in a server group at the same time, or at the same time a new instance is created. I don't think we have late validation for all those scenarios.
17:40:11 bauzas and when you say --min 1 --max 5, you'd expect that if you have room for 1, then only one would be created and 4 in ERROR, but that's not the case
17:40:13 cfriesen bauzas: me too. :) but last time I brought it up people wanted to keep it.
17:40:27 mriedem melwitt: kind of yeah
17:40:29 bauzas because min/max are only relevant wrt quotas
17:40:34 cfriesen bauzas: actually I'd expect that 1 would be created and the other 4 would be like they never existed
17:40:42 arvindn05 mriedem: thanks....any questions for me?
17:40:46 bauzas cfriesen: that's absolutely not the current behaviour
17:40:54 melwitt mriedem: okay, I'm cool with that. just wanted to make sure I understood
17:41:00 cfriesen bauzas: I know, but it should be given how it's documented in the API
17:41:01 mriedem arvindn05: not yet, still reading
17:41:17 bauzas the current behaviour is that if you asked for 10 instances but your quota only tells 2 left, then it will just check that
17:41:25 arvindn05 mriedem: great....just let me know when you have questions.
17:41:27 bauzas but honestly, who cares ?
17:41:34 mriedem bauzas: heh "Error handling for multiple create is not as consistent as for single server create, and there is no guarantee that all the servers will be built. This call should generally be avoided in favor of clients doing direct individual server creates."
17:41:39 mriedem so actually,
17:41:49 mriedem concurrent creates is actually a problem for the affinity scenarios
17:41:58 mriedem but not a single multi-create request
17:42:02 mriedem damned if you do, damned if yo udon't
17:42:28 bauzas I'm just saying that the "minimum" value is useless
17:42:46 bauzas you ask for a max of 10, the scheduler will try to find you room for 10, or kick all of them
17:42:53 mriedem maybe we should amend that to say, "unless of course you're creating servers in a server group, then because of race issues we have'nt fixed yet, you should use multi-create"
17:43:04 cfriesen bauzas: and it shouldn't kick all of them if some of them pass
17:43:21 bauzas cfriesen: I'm not sure
17:43:29 bauzas cfriesen: it's a capacity problem
17:43:37 cfriesen bauzas: the user has said "give me as many instances as you can, up to a max of 10"
17:43:39 bauzas and we shouldn't leak the capacity to the user
17:43:42 mriedem how is the min useless? give me at least 2, but 10 if you can
17:43:55 bauzas mriedem: the "if you can" is only quota-wise
17:44:04 cfriesen bauzas: no, it's in the boot request
17:44:31 bauzas cfriesen: but the info we give to the scheduler is "how many the user asked"
17:44:45 bauzas cfriesen: not "how many the user is agreeing to only have"
17:44:55 mriedem also depends on the port quota, don't forget
17:45:04 bauzas yeah
17:45:05 cfriesen bauzas: I totally agree it's all messed up. but the API describes it as the min/max nubmer of servers to be created
17:45:15 bauzas the API docs are wrong
17:45:28 cfriesen the API docs are by definition correct, the implementation is wrong. :)
17:45:49 cfriesen the user wants at least 2 and at most 10 instances. If the quota is 4, we should give them 4
17:45:54 bauzas that's an interesting PoV
17:45:56 cfriesen If we can only schedule 3, we should give them 3
17:46:08 mriedem i'm pretty sure we've said in the past that the docs don't define the api
17:46:11 dansmith cfriesen: I think the actual behavior, which people may have built dependencies on, is the canonical thing
17:46:13 mriedem the current behavior defines the api
17:46:16 dansmith right
17:46:16 mriedem right
17:46:18 mriedem right
17:46:21 dansmith right
17:46:22 melwitt right
17:46:23 mriedem right
17:46:24 bauzas right
17:46:26 bauzas right
17:46:28 bauzas right
17:46:42 dansmith (man we're dorks)
17:46:43 mriedem remember the docs of yore for the compute api were written by people that didn't actually code up nova api
17:46:57 melwitt I think we've said in the past that it makes more sense for the --min to be honored if we can but if we change that, we have to do it with a microversion
17:46:58 mriedem and until sdague lifted them in tree they were all sorts of wrong
17:47:02 mriedem and still are in parts
17:47:25 bauzas anyway, time to say goodbye
17:47:33 mriedem adieu
17:47:36 cfriesen have fun
17:48:05 bauzas "adieu" has a very strong meaning of a final goodbye :)
17:48:13 bauzas I just hope to be back in 5 days :)
17:48:14 cfriesen au revoir
17:49:22 cfriesen for what it's worth, it seems odd to say that nobody can trust our published API specification, and instead they have to observe the current behaviour.
17:50:16 cfriesen but I get the argument about people already depending on the current behaviour
17:54:11 melwitt I wonder if it only behaves that way for quota. like, what happens if you do --min 2 --max 10 and there's only compute capacity for 2. I wonder if that would pass scheduling and give back only 2 instances
17:54:13 dansmith cfriesen: I think it's odd to say that we'd jump through hoops which might be very difficult to implement something the way someone guessed it may have worked long ago
17:54:40 dansmith ...just because they put that in a doc
17:55:04 mriedem arvindn05: ok thanks for the clarifications. replies inline for what i'd like to see changed, but it should be trivial
17:55:36 mriedem cfriesen: if the docs are inaccurate, let's clean up the docs
17:55:46 mriedem coincidentally i was just looking at https://bugs.launchpad.net/nova/+bug/1684261 again
17:55:47 openstack Launchpad bug 1684261 in OpenStack Compute (nova) "AggregateImagePropertiesIsolation example doesn't actually indicate how it works" [Low,Confirmed]
17:56:44 arvindn05 mriedem: awesome...will review them and let you know
17:57:05 mriedem would be really nice if someone would take on fixing the doc for that filter
17:58:48 arvindn05 mriedem: sure. Updating the docs should be straitforward...will look into it
17:59:02 mriedem famous, last, words

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