On a Tesla T4 the backend exited during the first /generate with no
traceback and no HTTP response, leaving the client with
RemoteDisconnected and every later call with ConnectionRefused. Three
separate defects combined, which is why none of the reporter's
workarounds helped.
1. torch.compile(mode="reduce-overhead") captures CUDA graphs. T4
(sm_75) passed the existing arch gate, so capture was attempted and
aborted the process from inside the native CUDA library — below the
interpreter, where neither the #278 eager-fallback wrapper nor any
except clause can see it. The compile mode is now resolved per GPU:
Ampere (sm_80) and newer keep the cudagraph mode, older cards drop to
the non-cudagraph "default" mode and keep their compiled Inductor
kernels. Fails open on any probe error, so no GPU that works today
loses the optimization. OMNIVOICE_FORCE_CUDAGRAPH=1 restores it.
2. should_torch_compile() never read TORCH_COMPILE_DISABLE. main.py sets
it on win32, build_engine_env injected it into subprocesses, and
docs/install/windows.md tells users to export it — but the in-process
gate ignored it, so the reporter exported the documented variable and
still got "torch.compile applied". The gate now honours
TORCH_COMPILE_DISABLE / TORCHDYNAMO_DISABLE / TORCHINDUCTOR_DISABLE on
every platform, and an env opt-out on the parent propagates to engine
subprocesses. The settings DB path is logged alongside the toggle:
the reporter had three omnivoice.db files and edited one the backend
never opened.
3. Settings -> Performance -> "Disable torch.compile" was rendered
disabled outside Windows in both the Tauri and Electron UIs, so the
one control that would have stopped this was unreachable for the
affected Linux user. The toggle is now live on every platform, and
build_engine_env honours it everywhere rather than only on win32.
Also arms faulthandler before torch is imported, so a fatal native
signal writes the faulting thread's Python stack to backend_err.log
instead of the process vanishing silently. This does not prevent a
crash; it makes one diagnosable. OMNIVOICE_DISABLE_FAULTHANDLER=1 skips
it.
Tests fail before / pass after, verified by stashing the source and
running the new tests against unfixed code. The crash test kills a real
child interpreter with a real SIGSEGV and requires a named Python frame
in the output. test_torch_compile_path_gate's fixture now clears the
compile-disable env vars: main.py setdefaults them on win32, so on a
Windows runner they leaked into os.environ and decided those tests.
Not verified on real hardware — no Turing GPU available. The sm_80 floor
is inferred from the crash report and from docs/hardware-notes-tesla-t4.md,
which already flagged cudagraphs on T4 as attempted by default and never
evaluated.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
