[oslo][nova][stable][requirements] Fixing a high CPU usage from oslo.service into stable/rocky branch

Lee Yarwood lyarwood at redhat.com
Thu Nov 22 09:46:51 UTC 2018

On 22-11-18 15:55:07, Tony Breeds wrote:
> HI folks,
>     I admit my initial response to this was mor pragmatic 'take the
> bakport' but as I thought it through I saw more problems with that
> approach.
> On Wed, Nov 21, 2018 at 03:47:25PM +0100, Herve Beraud wrote:
> > Since these changes was introduced into oslo.service master, nova facing
> > some issues into the master CI process, due to the threading changes, and
> > they was fixed by these patches ( https://review.openstack.org/#/c/615724/,
> > https://review.openstack.org/#/c/617989/ ) into master.
> > 
> > Few weeks ago I have backport to oslo.service some changes (
> > https://review.openstack.org/#/c/614489/ ) from master to stable/rocky to
> > also fix the problem in the rocky release.
> Okay that was a mistake, backporting a patch from master to stable that
> is known to break consumers, I admit this isn't explicitly called out in
> the stable policy but it is kind of the spirit of the stable policy.
> The quickest fix would be to revert 614489, release 1.31.7 and blacklist
> 1.31.6.
> Yes this leaves the High CPU usage bug open on rocky.  That isn't great
> but it also isn't terrible.

Agreed, I'm in favor of doing this and asking the oslo.service team to
rework the original fix on stable/rocky into something that doesn't
break Nova CI.
> > When this backport was merged we have created a new release of oslo.service
> > (1.31.6) ( https://review.openstack.org/#/c/616505/ ) (stable/rocky
> > version).
> > 
> > Then the openstack proposal bot submit a patch to requirements on stable
> > rocky to update the oslo.service version with the latest version (1.31.6)
> > but if we'll use it we'll then break the CI
> > https://review.openstack.org/#/c/618834/ so this patch is currently blocked
> > to avoid nova CI error.
> Huzzah for cross-project gateing!
> > # Issue
> > 
> > Since the oslo.services threading changes were backported to rocky we risk
> > to  faces the same issues inside the nova rocky CI if we update the
> > requirements.
> > 
> > In parallel in oslo.service we have started to backport a new patch who
> > introduces fixture  ( https://review.openstack.org/#/c/617989/ ) from
> > master to rocky, and also we start to backport on nova rocky branch (
> > https://review.openstack.org/619019, https://review.openstack.org/619022 )
> > patches who use oslo.service.fixture and who solve the nova CI issue. The
> > patch on oslo.service exposes a public oslo_service.fixture.SleepFixture
> > for this purpose. It can be maintained opaquely as internals change without
> > affecting its consumers.
> > 
> > The main problem is that the patch bring a new functionality to a stable
> > branch (oslo.service rocky) but this patch help to fix the nova issue.
> > 
> > Also openstack proposal bot submit a patch to requirements on stable rocky
> > to update the oslo.service version with the latest version (1.31.6) but if
> > we'll use it we'll then break the CI
> > https://review.openstack.org/#/c/618834/ since the oslo service 1.31.6 is
> > incompatible with novas stable rocky unittest due to the threading changes.
> > 
> > # Questions and proposed solutions
> > 
> > This thread try to summarize the current situation.
> > 
> > We need to find how to be able to proceed, so this thread aim to allow to
> > discuss between team to find the best way to fix.
> > 
> > 1. Do we need to continue to try to backport fixture on oslo.service to fix
> > the CI problem (https://review.openstack.org/#/c/617989/) ?
> Doing this is a violation of the stable policy.  I get that the new
> feature is just a testing only fixture but that doesn't really matter
> it's still a feature.  To use it consumers would need to raise
> the value for oslo.service in lower-constraints.txt which is a policy
> violation.

I'm being slightly dense this morning, I can't seem to find a reference
to this lower-constraints.txt policy anywhere in the stable docs:


> The is an additional complication that this backport adds fixtures to
> requirements.txt for oslo.service, at the very least this would mean
> we're into a minor semver bump (1.32.X, which is already taken).  This
> also means the vendors need to ensure that there is a 'fixtures' package
> available.  Now I expect that all packagers have such a thing but there
> is a small chance that it exists as a build only package and needs to be
> exposed/published.  We're previously said to vendors we wouldn't do that
> on stable branches.

I wouldn't be concerned with the impact on packagers and more that we
can't use 1.32.x anyway thus blocking this approach.
> > 2. Do we need to find an another approach like mocking
> > oslo.service.loopingcall._Event.wait in nova instead of mocking
> > oslo_service.loopingcall._ThreadingEvent.wait (example:
> > https://review.openstack.org/#/c/616697/2/nova/tests/unit/compute/test_compute_mgr.py)
> > ?
> > This is only a fix on the nova side and it allows us to update oslo.service
> > requirements and allows us to fix the high CPU usage issue. I've submit
> > this patch (https://review.openstack.org/619246) who implement the
> > description above.
> > 
> > Personaly I think we need to find an another approach like the mocking
> > remplacement (c.f 2).
> > 
> > We need to decide which way we use and to discuss about other solutions.
> I think the only way forward is the revert, release and block path.  The
> existing open reviews just add more policy violations.

Again I agree.


Lee Yarwood                 A5D1 9385 88CB 7E5F BE64  6618 BCA6 6E33 F672 2D76
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