On Fri, Sep 18, 2020 at 4:31 PM Dan Liew dan@su-root.co.uk wrote:
On Wed, 16 Sep 2020 at 22:24, David Blaikie dblaikie@gmail.com wrote:
I appreciate the value of the feature - but it's possible the test doesn't pull its weight. Is the code that implements the feature liable to failure/often touched? If it's pretty static/failure is unlikely, possibly the time and flaky failures aren't worth the value of possibly catching a low-chance bug.
I don't have many data points here. I haven't needed to touch the code or tests since 2018. I haven't been asked to review any patches related to the timeout feature since then so I presume nobody has touched it since.
Another option might be to reduce how often/in which configurations the test is run - LLVM_ENABLE_EXPENSIVE_CHECKS presumably only works for code within LLVM itself, and not test cases - but maybe I'm wrong there & this parameter could be used (& then the timing bumped up quite a bit to try to make it much more reliable), or something similar could be implemented at the lit check level?
Ah, compiler-rt tests use EXPENSIVE_CHECKS to disable certain tests:
./compiler-rt/test/lit.common.configured.in:set_default("expensive_checks", @LLVM_ENABLE_EXPENSIVE_CHECKS_PYBOOL@) ./compiler-rt/test/fuzzer/large.test:UNSUPPORTED: expensive_checks
Could you bump the timeouts a fair bit and disable the tests except under expensive checks?
Only running that test in the "expensive_checks" configuration kind of abuses that configuration option because the test is actually not an expensive check.
Ah, sorry - my point was to make it expensive: Make it long enough that it's more reliable even when the machine is under load. But making it long makes it expensive, so then classify it as such.
It's just that the test is sensitive to the performance of the running system. If the system is under heavy load when the test is running it's more likely to fail.
One thing we could do to remove fragility in the test is to remove the running of `short.py` in the test. This is only invoked to check that it's possible for a command to run to completion in the presence of a fixed timeout. If we can live without testing that part (i.e. we only test that a timeout can be reached) then the test should be much more robust.
If you're on board with that, it's a tradeoff I think is probably reasonable from a test coverage V reliability V development time tradeoff.
If for some reason that's not enough another thing that might help with this problem is to not run the lit tests at the same time as all the other tests. The hope here is that the lit tests would run while the system load is lower. We could do this by changing the build system to
- Make all `check-*` (except `check-lit`) targets depend on the
`check-lit` target. This would ensure that lit gets tested before we test everything else in LLVM.
- Remove the lit test directory from inclusion in all `check-*`
targets (except `check-lit`) so we don't test lit twice.
This also has a nice benefit of testing lit **before** we use it to test everything else in LLVM. Today we don't do that, we just run all the tests in one big lit invocation (i.e. we test lit at the same time that we are using it). It does have some downsides though
- If any of the lit tests fail we won't run the rest of the tests so
you won't get the results of running the other tests until the lit tests are fixed.
- When running any of the `check-*` targets (apart from `check-lit`)
you have to wait for the lit tests to run before any other tests run.
Reckon that's probably not the best way to go - wouldn't totally fix this bug (buildbot might be busy for other reasons (maybe it's running some regular maintenance, etc) or lit tests might still saturate cores & slow down the test) & would slow down test iteration by having another "pinch point" in the build graph - waiting for the last of the lit tests to run (this kind of period reduces core utilization - as the last few tests finish and no new work is scheduled) before starting up all the cores again to run the next batch of tests.
- Dave
What do you think?
On Wed, Sep 16, 2020 at 9:31 PM Dan Liew dan@su-root.co.uk wrote:
Hi David,
Unfortunately writing a reliable test is tricky given that the functionality we're trying to test involves timing. I would advise against disabling the test entirely because it actually tests functionality that people use. I'd suggest bumping up the time limits. This is what I've done in the past. See
commit 6dfcc78364fa3e8104d6e6634733863eb0bf4be8 Author: Dan Liew dan@su-root.co.uk Date: Tue May 22 15:06:29 2018 +0000
[lit] Try to make `shtest-timeout.py` test more reliable by using a larger timeout value. This really isn't very good because it will still be susceptible to machine performance. While we are here also fix a bug in validation of `maxIndividualTestTime` where previously it wasn't checked if the type was an int. rdar://problem/40221572 llvm-svn: 332987HTH, Dan.
On Wed, 16 Sep 2020 at 09:37, David Blaikie dblaikie@gmail.com wrote:
Ping on this
On Wed, Sep 9, 2020 at 8:27 PM David Blaikie dblaikie@gmail.com wrote:
The clang-cmake-armv8-lld (linaro-toolchain owners) buildbot is timing out trying to run some timeout tests (Dan Liew author):
Pass: http://lab.llvm.org:8011/builders/clang-cmake-armv8-lld/builds/5672 Fail: http://lab.llvm.org:8011/builders/clang-cmake-armv8-lld/builds/5673
Is there anything we can do to the buildbot? Or the tests? (bump up the time limits or maybe remove the tests as unreliable?)