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

[Stephen Huan via llvm-commits]

stephen-huan wrote:

> Have you tried getting a stack trace?

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).

> I would probably need some convincing that this is a problem with llvm-exegesis itself rather than your environment to accept this patch.

Sure, I'm building llvm with the [nix](https://nixos.org/) package manager which tries to guarantee a completely deterministic build environment for reproducibility (nix builds packages in a sandbox which only allows access to other nix packages, so ideally builds would be bit-for-bit reproducible). That is to say, there are very few environment-specific impurities outside of hardware (my system doesn't have a `/bin`, `/lib`, or `/usr` for example). 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 (88bf774c565080e30e0a073676c316ab175303af) on a different computer (a slurm cluster) and I can't reproduce. This desktop is strange I guess.

<details>
<summary>desktop information</summary>

```text
Dell Precision 3680

Host: Dell Inc. 0VTKY7
CPU: Intel i7-14700K (28) @ 5.500GHz
GPU: NVIDIA GeForce RTX 4070
GPU: Intel Raptor Lake-S GT1 [UHD Graphics 770]

Architecture:             x86_64
  CPU op-mode(s):         32-bit, 64-bit
  Address sizes:          46 bits physical, 48 bits virtual
  Byte Order:             Little Endian
CPU(s):                   28
  On-line CPU(s) list:    0-27
Vendor ID:                GenuineIntel
  Model name:             Intel(R) Core(TM) i7-14700K
    CPU family:           6
    Model:                183
    Thread(s) per core:   2
    Core(s) per socket:   20
    Socket(s):            1
    Stepping:             1
    CPU(s) scaling MHz:   35%
    CPU max MHz:          5600.0000
    CPU min MHz:          800.0000
    BogoMIPS:             6835.20
    Flags:                fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat p
                          se36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdp
                          e1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl
                           xtopology nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqd
                          q dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pd
                          cm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xs
                          ave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb ssbd
                          ibrs ibpb stibp ibrs_enhanced tpr_shadow flexpriority ept vpid ept_
                          ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid rdseed adx
                          smap clflushopt clwb intel_pt sha_ni xsaveopt xsavec xgetbv1 xsaves
                           split_lock_detect user_shstk avx_vnni dtherm ida arat pln pts hwp
                          hwp_notify hwp_act_window hwp_epp hwp_pkg_req hfi vnmi umip pku osp
                          ke waitpkg gfni vaes vpclmulqdq rdpid movdiri movdir64b fsrm md_cle
                          ar serialize pconfig arch_lbr ibt flush_l1d arch_capabilities
Virtualization features:
  Virtualization:         VT-x
Caches (sum of all):
  L1d:                    768 KiB (20 instances)
  L1i:                    1 MiB (20 instances)
  L2:                     28 MiB (11 instances)
  L3:                     33 MiB (1 instance)
NUMA:
  NUMA node(s):           1
  NUMA node0 CPU(s):      0-27
Vulnerabilities:
  Gather data sampling:   Not affected
  Itlb multihit:          Not affected
  L1tf:                   Not affected
  Mds:                    Not affected
  Meltdown:               Not affected
  Mmio stale data:        Not affected
  Reg file data sampling: Mitigation; Clear Register File
  Retbleed:               Not affected
  Spec rstack overflow:   Not affected
  Spec store bypass:      Mitigation; Speculative Store Bypass disabled via prctl
  Spectre v1:             Mitigation; usercopy/swapgs barriers and __user pointer sanitizatio
                          n
  Spectre v2:             Mitigation; Enhanced / Automatic IBRS; IBPB conditional; RSB fillin
                          g; PBRSB-eIBRS SW sequence; BHI BHI_DIS_S
  Srbds:                  Not affected
  Tsx async abort:        Not affected
```

</details>

> Also, what LLVM version is this with?

19.1.7 and latest master (tried a66376b0dc3b2ea8a84fda26faca287980986f78, e6de45a22933114a1d9421dad558a3d62546cb53). The earliest release I could find with the code was 17.0.0 (88bf774c565080e30e0a073676c316ab175303af) but I haven't tried it with this desktop yet.

Don't feel strongly about this PR, in any case we can maintain the patch downstream.

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