Re: [PATCH 4/4] ci: Add check-migration-quick to the clang job

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Oct 18, 2024 at 10:51:03AM -0300, Fabiano Rosas wrote:
> Daniel P. Berrangé <berrange@redhat.com> writes:
> 
> > On Fri, Oct 18, 2024 at 10:46:55AM +0100, Peter Maydell wrote:
> >> On Fri, 18 Oct 2024 at 10:01, Daniel P. Berrangé <berrange@redhat.com> wrote:
> >> >
> >> > On Thu, Oct 17, 2024 at 01:29:35PM -0300, Fabiano Rosas wrote:
> >> > > Daniel P. Berrangé <berrange@redhat.com> writes:
> >> > >
> >> > > > On Thu, Oct 17, 2024 at 11:32:11AM -0300, Fabiano Rosas wrote:
> >> > > >> Recent changes to how we invoke the migration tests have
> >> > > >> (intentionally) caused them to not be part of the check-qtest target
> >> > > >> anymore. Add the check-migration-quick target so we don't lose
> >> > > >> migration code testing in this job.
> >> > > >
> >> > > > But 'check-migration-quick' is only the subset of migration tests,
> >> > > > 'check-migration' is all of the migration tests. So surely this is
> >> > > > a massive regressions in covage in CI pipelines.
> >> > >
> >> > > I'm not sure it is. There are tests there already for all the major
> >> > > parts of the code: precopy, postcopy, multifd, socket. Besides, we can
> >> > > tweak migration-quick to cover spots where we think we're losing
> >> > > coverage.
> >> >
> >> > Each of the tests in migration-test  were added for a good reason,
> >> > generally to address testing gaps where we had functional regressions
> >> > in the past. I don't think its a good idea to stop running such tests
> >> > in CI as gating on new contributions. Any time we've had optional
> >> > tests in QEMU, we've seen repeated regressions in the area in question.
> >> >
> >> > > Since our CI offers nothing in terms of reproducibility or
> >> > > debuggability, I don't think it's productive to have an increasing
> >> > > amount of tests running in CI if that means we'll be dealing with
> >> > > timeouts and intermittent crashes constantly.
> >> >
> >> > Test reliability is a different thing. If a particular test is
> >> > flaky, it needs to either be fixed or disabled. Splitting into
> >> > a fast & slow grouping doesn't address reliability, just hides
> >> > the problem from view.
> >> 
> >> A lot of the current reliability issue is timeouts -- sometimes
> >> our CI runners just run really slow (I have seen an example where
> >> between a normal and a slow run on the same commit both the
> >> compile and test times were 10x different...) So any test
> >> that is not a fast-to-complete is much much more likely to
> >> hit its timeout if the runner is running slowly. When I am
> >> doing CI testing for merges "migration test timed out again"
> >> is really really common.
> >
> > If its frequently timing out, then we've got the timeouts
> > wrong, or we have some genuine bugs in there to be fixed.
> >
> >> > > No disagreement here. But then I'm going to need advice on what to do
> >> > > when other maintainers ask us to stop writing migration tests because
> >> > > they take too long. I cannot send contributors away nor merge code
> >> > > without tests.
> >> >
> >> > In general, I think it is unreasonable for other maintainers to
> >> > tell us to stop adding test coverage for migration, and would
> >> > push back against such a request.
> >> 
> >> We do not have infinite CI resources, unfortunately. Migration
> >> is competing with everything else for time on CI. You have to
> >> find a balance between "what do we run every time" and "what
> >> do we only run when specifically testing a migration pullreq".
> >> Similarly, there's a lot of iotests but we don't run all of them
> >> for every block backend for every CI job via "make check".
> >
> > The combos we don't run for iotests are a good source of
> > regressions too :-(
> >
> >> Long test times for tests run under "make check" are also bad
> >> for individual developers -- if I'm running "make check" to
> >> test a target/arm change I've made I don't really want that
> >> to then spend 15 minutes testing the migration code that
> >> I haven't touched and that is vanishingly unlikely to be
> >> affected by my patches.
> >
> > Migration-test *used* to take 15 minutes to run, but that was a
> > very long time ago. A run of it today is around 1m20.
> >
> > That said, if you are building multiple system emulators, we
> > run the same test multiple times, and with the number of
> > targets we have, that will be painful.
> >
> > That could be a good reason to split the migration-test into
> > two distinct programs. One program that runs for every target,
> > and one that is only run once, for some arbitrary "primary"
> > target ?
> 
> What do you mean by distinct programs? It's not the migration-test that
> decides on which targets it runs, it's meson.build. We register a test()
> for each target, same as with any other qtest. Maybe I misunderstood
> you...

If we split, we could have meson.build register "migration-smoketest"
for every target while registering "migration-bigtest" for just 1 target.

> >  Or could we make use of glib's g_test_thorough
> > for this - a primary target runs with "SPEED=through" and
> > all other targets with normal settings. That would give us
> > a way to optimize any of the qtests to reduce redundant
> > testing where appropriate.
> 
> This still requires a new make target I think. Otherwise we'd run *all*
> thorough tests for a QEMU target and not only migration-test in thorough
> mode.

Yes, that's true, having separate programs is probably an easier
option than playing games with "SPEED" settings.


With regards,
Daniel
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