Le 15/08/2014 15:35, Andrew Laski a écrit :
On 08/14/2014 03:21 AM, Nikola Đipanov wrote:On 08/13/2014 06:05 PM, Sylvain Bauza wrote:Le 13/08/2014 12:21, Sylvain Bauza a écrit :Le 12/08/2014 22:06, Sylvain Bauza a écrit :Le 12/08/2014 18:54, Nikola Đipanov a écrit :On 08/12/2014 04:49 PM, Sylvain Bauza wrote:(sorry for reposting, missed 2 links...) Hi Nikola, Le 12/08/2014 12:21, Nikola Đipanov a écrit :Well, ERT does provide a plugin mechanism for testing resources at the claim level. This is the plugin responsibility to implement a test()Hey Nova-istas,While I was hacking on [1] I was considering how to approach the factthat we now need to track one more thing (NUMA node utilization) in our resources. I went with - "I'll add it to compute nodes table" thinking it's a fundamental enough property of a compute host that it deserves to be there, although I was considering Extensible Resource Tracker at one point (ERT from now on - see [2]) but looking at the code - it did not seem to provide anything I desperately needed, so I went with keeping it simple. So fast-forward a few days, and I caught myself solving a problem that Ikept thinking ERT should have solved - but apparently hasn't, and I think it is fundamentally a broken design without it - so I'd reallylike to see it re-visited. The problem can be described by the following lemma (if you take 'lemma' to mean 'a sentence I came up with just now' :)): """ Due to the way scheduling works in Nova (roughly: pick a host based on stale(ish) data, rely on claims to trigger a re-schedule), _same exact_ information that scheduling service used when making a placement decision, needs to be available to the compute service when testing the placement. """ This is not the case right now, and the ERT does not propose any way to solve it - (see how I hacked around needing to be able to getextra_specs when making claims in [3], without hammering the DB). The result will be that any resource that we add and needs user suppliedinfo for scheduling an instance against it, will need a buggy re-implementation of gathering all the bits from the request that scheduler sees, to be able to work properly.method [2.1] which will be called when test_claim() [2.2] So, provided this method is implemented, a local host check can be done based on the host's view of resources.Yes - the problem is there is no clear API to get all the needed bits to do so - especially the user supplied one from image and flavors. On top of that, in current implementation we only pass a hand-wavy'usage' blob in. This makes anyone wanting to use this in conjunctionwith some of the user supplied bits roll their own'extract_data_from_instance_metadata_flavor_image' or similar which ishorrible and also likely bad for performance.I see your concern where there is no interface for user-facing resources like flavor or image metadata. I also think indeed that the big 'usage' blob is not a good choice for long-term vision. That said, I don't think as we say in French to throw the bath water... ie. the problem is with the RT, not the ERT (apart themention of third-party API that you noted - I'll go to it later below)This is obviously a bigger concern when we want to allow users to pass data (through image or flavor) that can affect scheduling, but still a huge concern IMHO.And here is where I agree with you : at the moment, ResourceTracker (and consequently Extensible RT) only provides the view of the resources thehost is knowing (see my point above) and possibly some other resourcesare missing.So, whatever your choice of going with or without ERT, your patch [3] still deserves it if we want not to lookup DB each time a claim goes.As I see that there are already BPs proposing to use this IMHO broken ERT ([4] for example), which will surely add to the proliferation of code that hacks around these design shortcomings in what is already aTwo distinct implementations of that spec (ie. instances and flavors) have been proposed [2.3] [2.4] so reviews are welcome. If you see the test() method, it's no-op thing for both plugins. I'm open to commentsmessy, but also crucial (for perf as well as features) bit of Nova code.because I have the stated problem : how can we define a limit on just a counter of instances and flavors ?Will look at these - but none of them seem to hit the issue I am complaining about, and that is that it will need to consider other request data for claims, not only data available for on instances.Also - the fact that you don't implement test() in flavor ones tells me that the implementation is indeed racy (but it is racy atm as well) and two requests can indeed race for the same host, and since no claims are done, both can succeed. This is I believe (at least in case of singleflavor hosts) unlikely to happen in practice, but you get the idea.Agreed, these 2 patches probably require another iteration, in particular how we make sure that it won't be racy. So I need another run to think about what to test() for these 2 examples. Another patch has to be done for aggregates, but it's still WIP so not mentioned here. Anyway, as discussed during today's meeting, these 2 patches will not be based on ERT because of the risk it goes for Juno so let's scope them out of this thread.RT does not miss info about the host, but about the particular requestI propose to revert [2] ASAP since it is still fresh, and see how we can come up with a cleaner design.Would like to hear opinions on this, before I propose the patch tho!IMHO, I think the problem is more likely that the regular RT misses some information for each host so it requires to handle it on a case-by-case basis, but I don't think ERT either increases complexity or creates another issue.which we have to fish out of different places like image_metadata extra_specs etc, yet - it can't really work without them. This is definitely a RT issue that is not specific to ERT.+1, I agree with you, that's an API issue for RT : how do we pass out user-defined metrics ? I still need to figure out which kind of usecases are requiring such examples, albeit the NUMA usecase of course.After a night and morning of thinking about this problem, I'm writing down some ideas that could help fixing the problem (although I don't think it's a long-term scenario, rather a workaround) : Considering you need the metadata of the flavor asked by user when claiming a resource : 1. Compute Manager knows request_spec when building an instance, so it could pass out request_spec as paramater (optional or not) to rt.instance_claim() in the claim context 2. As ERT does, when claiming, it calls the ERT plugin .test() method so with request_spec as extra parameter 3. On the ERT side, a plugin is responsible for calling (and caching) all flavors metadata, or even only the key you need to compare 4. Scheduler knows flavors metadata thanks to ERT plugin and blueprintisolate-scheduler-db so it makes decisions on the same subset as the RT5. When claiming in ERT plugin test(), it extracts the flavor_id, looks at the internal in-memory representation of flavors to get the metadata, and calls the NUMA _test_numa_topology() method for checking wrt this flavor metadata The idea is that so filters and claims are doing separate decisions on the same source of knowledge, here being ERT. -SylvainJust made a draft over my thoughts here : https://review.openstack.org/113936I have commented on the review itself in more detail, but in short -this solution won't work for me, and thus in the general case as well, as1) we need a way to persist the request data (and not make it a horrible performance bottleneck), as caching won't cut it.There's a proposal to persist some data already at http://git.openstack.org/cgit/openstack/nova-specs/tree/specs/juno/persistent-resource-claim.rst . Based on this discussion it seems like we might want to revisit that to ensure it's going to do the right thing, or can be extended to later.
Well, correct me if I'm wrong but this blueprint you mentioned is about reducing the number of DB calls when the compute node is starting by persisting existing claims into a local storage.
I had many concerns about this bp and how it was designed so maybe I'm not a good advocate for it, but even that said, IMHO I think it covers a separate problem (although it can help wrt restarts) Here, the problem is that we need an hacky thing to get metadata associated to the flavor passed in the request data, so we need to figure out how RT can decide OK or KO based on the same metrics as for the scheduler (but with the slight but not minor difference that Compute has a better view of its own resources)
My personal feeling is that we need to update Scheduler host state by posting metrics updates from the Compute, so we change how the Scheduler decides from a polling model to an async model with pulls, where the single source has to be the Compute ResourceTracker. Of course, that deserves to improve how updates are done from the RT to the Scheduler (eg. not waiting 60 secs for sending updates about flavors or instances related to/running into the host, but rather notify the Scheduler immediatly), and that also needs to think about passing request data into claims.
-Sylvain
2) We also need a way to use it in every periodic task run. None of this is only ERT problem, they are problems of the RT itself, but as I have said in the thread already - adding a plugin API on top of something that is broken is just asking for all sorts of trouble. Still leaning towards revert really - anything else would be short sighted. I would be happy to help come up with a baseline of things to fix before we can add it back, to avoid deferring it needlesly due to scope creep. N.-SHowever, I still see several issues with the current ERT implementation,but the one I am getting at here, and why I think we should revert it, is that we are building a 3rd party plugin API that is tightly coupledto an obviously flawed internal API (RT and Claims). We have no policy AFIK about what guarantees we provide to 3rd party plugins, but if we are going to be breaking them all the time, or inthis case providing very limited usefulness - I see little value in thecurrent implementation of ERT, and see issues with it staying, which means future work will be based on it. N.*This* is to me IMHO the biggest problem with ERT : if we say that we externalize an API for 3rd-party plugins, we need to make sure that everything is handled. That said, instead of reverting the whole patch, could we just consider to only accept changes that wouldn't require user-facing metrics ? The existing VCPU implementation still sounds good to me, so we can just consider a clear communication on what is acceptable and what not (ie. a docstring in the plugin API or so., plus -2/-1 reviews if needed) -SylvainThanks, -SylvainThanks all, Nikola [1]https://blueprints.launchpad.net/nova/+spec/virt-driver-numa-placement[2] https://review.openstack.org/#/c/109643/ [3] https://review.openstack.org/#/c/111782/ [4] https://review.openstack.org/#/c/89893 _______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev[2.1]https://github.com/openstack/nova/blob/master/nova/compute/resources/__init__.py#L75[2.2]https://github.com/openstack/nova/blob/master/nova/compute/claims.py#L134[2.3] https://review.openstack.org/112578 [2.4] https://review.openstack.org/113373 _______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev_______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev_______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev_______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev_______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev_______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev_______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
_______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
