[libcxx-commits] [libcxx] [llvm] [openmp] [lit] Add a flag to disable lit time tests (PR #98270)

[James Henderson via libcxx-commits]

https://github.com/jh7370 commented:

I think this looks good, but I just want to make sure I understand the motivation properly.

By default, lit records the time each individual test takes, in a file. If that file exists, it runs the tests in the order slowest to fastest, to avoid a long tail. I think the bit I'm uncertain about is how this interferes with what other build systems do? From what you've written, I believe you're saying that other build systems run subsets of the tests independently of other subsets, then because these subsets are running at the same time as each other, multiple lit invocations attempt to write to the same file at the same file potentially, which obviously isn't going to go well. Am I correct with this?

Would the "ordered by time taken" feature still be useful for these other systems (ignoring for a moment that this is controlled via the test times file)? If the feature would still be useful, I'm thinking that this PR is actually not really solving the heart of the problem, namely that running multiple lit invocations in the same section won't go well. Indeed, arguably the external build systems aren't even that relevant here: I've been known in the past to run lit in two different LLVM test directories myself at the same time for various reasons. Thoughts?

https://github.com/llvm/llvm-project/pull/98270