[lldb-dev] serialized, low-load test pass in parallel test runner

Reid Kleckner via lldb-dev lldb-dev at lists.llvm.org
Fri Nov 27 12:34:20 PST 2015

Chromium's test framework uses the same technique. It has the potential to
really slow things down if you have a lot of failing tests. You might want
some kind of threshold for giving up, I.e. here's 50 failures, I'll stop
running the rest so devs see results sooner.

Otherwise, yeah, this seems reasonable for lldb.

Sent from phone
On Nov 27, 2015 10:57 AM, "Todd Fiala via lldb-dev" <lldb-dev at lists.llvm.org>

> Hi all,
> On OS X (and frankly on Linux sometimes as well, but predominently OS X),
> we have tests that will sometimes fail when under significant load (e.g.
> running the concurrent test suite, exacerbated if we crank up the number of
> threads, but bad enough if we run at "number of concurrent workers ==
> number of logical cores").
> I'm planning on adding a serialized, one-worker-only phase to the end of
> the concurrent test run, where the load is much lighter since only one
> worker will be processing at that phase.  Then, for tests that fail in the
> first run, I'd re-run them in the serialized, single worker test run
> phase.  On the OS X side, this would eliminate a significant number of test
> failures that are both hard to diagnose and hard to justify spending
> significant amounts of time on in the short run.  (There's a whole other
> conversation to have about fixing them for real, i.e. working through all
> the race and/or faulty test logic assumptions that are stressed to the max
> under heavier load, but practically speaking, there are so many of them
> that this is going to be impractical to address in the short/mid term.).
> My question to all of you is if we'd want this functionality in top of
> tree llvm.org lldb.  If not, I'll do it in one of our branches.  If so,
> we can talk about possibly having a category or some other mechanism if we
> want to mark those tests that are eligible to be run in the follow-up
> serialized, low-load pass.  Up front I was just going to allow any test to
> fall into that bucket.  The one benefit to having it in top of tree
> llvm.org is that, once I enable test reporting on the green dragon public
> llvm.org OS X LLDB builder, that builder will be able to take advantage
> of this, and will most certainly tag fewer changes as breaking a test (in
> the case where the test is just one of the many that fail under high load).
> Let me know your thoughts either way.
> Thanks!
> --
> -Todd
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