[llvm] [llvm-exegesis] Timeout if subprocess executor hangs (PR #132861)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

> What should I run exactly? Sorry, not very knowledgeable, just building llvm for other projects ([triton-cpu](https://github.com/triton-lang/triton-cpu), packaging).

Attach lldb to the `llvm-exegesis` process that is hanging and then run `bt`. Maybe on the subprocess too that gets spawned, although that is a lot more complicated to collect. You need to attach a debugger to the main process, manually execute a `PTRACE_DETACH` from within that process, make sure a `SIGSTOP` is sent correctly, and then attach a debugger to the child process. The debugging might be more effort than it's worth though, depending upon how deep you're willing to dig into the issue.

> Unfortunately others (https://github.com/NixOS/nixpkgs/pull/392651#issuecomment-2749478493) can't reproduce it either and I haven't experienced it on my laptop (running roughly the same system). I also tried 17.0.0 (https://github.com/llvm/llvm-project/commit/88bf774c565080e30e0a073676c316ab175303af) on a different computer (a slurm cluster) and I can't reproduce. This desktop is strange I guess.

To me this further suggests it's something weird with your system rather than the test/code itself. These tests don't get exercised as much as they probably should as they need bare metal hardware access for performance counters (might be good to double check with other people that can't reproduce that the tests are actually running and not just disabled), but they do get run on lots of systems, and there haven't been any reports until now.

https://github.com/llvm/llvm-project/pull/132861