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

[Stephen Huan via llvm-commits]

stephen-huan wrote:

After applying https://github.com/llvm/llvm-project/commit/e696f4e5008c21b8edee089fb80d4e2e0d998e20 I still get the hang (and stack trace the same). Simpler reproduction, hangs on the following.

```bash
./build/bin/llvm-exegesis -mode latency -opcode-name=ADD64rr -x86-lbr-sample-period 123 -repetition-mode loop
```

When it doesn't hang I get the error

```text
llvm-exegesis error: can't run 'latency' mode, sched model does not define a cycle counter. You can pass --benchmark-phase=... to skip the actual benchmarking or --use-dummy-perf-counters to not query the kernel for real event counts.
```

So it either gives the above warning or hangs. The three calls I mentioned in https://github.com/llvm/llvm-project/pull/132861#issue-2944977746 map to

```bash
./build/bin/llvm-exegesis -mode latency -opcode-name=ADD64rr
./build/bin/llvm-exegesis -mode uops -opcode-name=ADD64rr
./build/bin/llvm-exegesis -mode latency -opcode-name=ADD64rr -x86-lbr-sample-period 123 -repetition-mode loop
```

```
llvm-exegesis error: can't run 'latency' mode, sched model does not define a cycle counter. You can pass --benchmark-phase=... to skip the actual benchmarking or --use-dummy-perf-counters to not query the kernel for real event counts.
llvm-exegesis error: can't run 'uops' mode, sched model does not define uops or issue counters. You can pass --benchmark-phase=... to skip the actual benchmarking or --use-dummy-perf-counters to not query the kernel for real event counts.
llvm-exegesis error: can't run 'latency' mode, sched model does not define a cycle counter. You can pass --benchmark-phase=... to skip the actual benchmarking or --use-dummy-perf-counters to not query the kernel for real event counts.
```

> It's actually interesting that this test ran at all on your system.

I'm not sure which test you're referring to exactly, but to be clear I was running `ninja -C build check-all` which loads the configuration `llvm/test/tools/llvm-exegesis/lit.local.cfg` regardless of whether the tests are unsupported or not. Since I get a return code 1 for those three calls, many of the llvm-exegesis tests are unsupported. That is, I get

```bash
ninja -C build test/check-llvm-tools-llvm-exegesis
```

```text
Testing Time: 1.17s

Total Discovered Tests: 102
  Unsupported: 29 (28.43%)
  Passed     : 73 (71.57%)
```


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