Skip the GPT interpreter tests on Windows

Six tests intermittently kill their xdist worker on windows-latest:

  Windows fatal exception: code 0xc000001d
  [gw1] node down: Not properly terminated

Always the same six, all of which interpret a whole GPT model, and on
about half the runs. They fail on released and nightly torch alike, and
the branch they fail on has passed with the same torch on other runs, so
this is the machine the job lands on rather than anything in the tree.

The previous attempt here set ATEN_CPU_CAPABILITY=default on Windows, on
the theory that the wheels carry AVX-512 instructions inside kernels
compiled for the AVX2 target. A diagnostic step confirmed the capability
was applied, and all six still crashed, so that theory is wrong and the
workflow change is reverted.

The fault is in native code, below any Python frame, so it cannot be
caught or retried in process: it takes the worker down and pytest only
ever sees a dead channel. Skip them on Windows until the crash is
understood. The same models stay covered on Linux and macOS.

Author: bhimrazy

.github/workflows/ci-testing.yml

@@ -45,16 +45,6 @@ jobs:
     # Timeout: https://stackoverflow.com/a/59076067/4521646
     timeout-minutes: 35
 
-    env:
-      # torch's Windows CPU wheels carry AVX-512 instructions inside kernels compiled for the
-      # AVX2 target, so on a runner whose CPU stops at AVX2 they fault with
-      # STATUS_ILLEGAL_INSTRUCTION (0xc000001d) and take the xdist worker down with them. The
-      # reported fault sits in the bfloat16 vector helpers, which is why the nanogpt and litgpt
-      # tests are the ones that crash: they are the only ones here running a model in bfloat16.
-      # Fall back to the unvectorized kernels on Windows until this is fixed upstream.
-      # Ref: https://github.com/pytorch/pytorch/issues/145702
-      ATEN_CPU_CAPABILITY: ${{ startsWith(matrix.os, 'windows') && 'default' || '' }}
-
     steps:
       - uses: actions/checkout@v5
       - name: Set up Python ${{ matrix.python-version }}
@@ -111,12 +101,6 @@ jobs:
             --extra-index-url=${TORCH_URL}
           pip list
 
-      - name: Show CPU dispatch
-        # So a green Windows run can be told apart from a run that happened to land on a CPU
-        # the bad kernels do not fault on. Expect DEFAULT here, not AVX2.
-        if: runner.os == 'Windows'
-        run: python -c "import torch; print('cpu capability:', torch.backends.cpu.get_cpu_capability())"
-
       - name: Testing Local
         if: matrix.suite == 'core'
         run: |

thunder/tests/framework.py

@@ -58,6 +58,10 @@ class NOTHING:
 )
 IS_WINDOWS = platform.system() == "Windows"
 
+# NOTE Interpreting a whole GPT model intermittently kills the process on Windows with an illegal
+#   instruction, in native code below any frame we could catch. Still covered on Linux and macOS.
+WINDOWS_GPT_CRASH_REASON = "intermittently crashes the test process on Windows (0xc000001d)"
+
 
 def _bitsandbytes_available():
     if not package_available("bitsandbytes"):

thunder/tests/test_interpreter.py

@@ -11,7 +11,7 @@
 import pytest
 import torch
 from torch.testing import assert_close
-from thunder.tests.framework import IS_WINDOWS
+from thunder.tests.framework import IS_WINDOWS, WINDOWS_GPT_CRASH_REASON
 
 import thunder
 from thunder.core.interpreter import (
@@ -3413,6 +3413,7 @@ def test_nanogpt_block(jit):
     assert_close(result, fn(*args, **kwargs))
 
 
+@pytest.mark.skipif(IS_WINDOWS, reason=WINDOWS_GPT_CRASH_REASON)
 def test_nanogpt(jit):
     from thunder.benchmarks import NanoGPTBenchmark, NanoGPTConfig, _nanogpt_configs
 
@@ -3428,6 +3429,7 @@ def test_nanogpt(jit):
     assert_close(result, fn(*args, **kwargs))
 
 
+@pytest.mark.skipif(IS_WINDOWS, reason=WINDOWS_GPT_CRASH_REASON)
 def test_litgpt(jit):
     from thunder.benchmarks import LitGPTBenchmark
     from thunder.tests.litgpt_model import Config

thunder/tests/test_jit_general.py

@@ -14,7 +14,7 @@
 
 import thunder
 
-from thunder.tests.framework import requiresCUDA, IS_WINDOWS
+from thunder.tests.framework import requiresCUDA, IS_WINDOWS, WINDOWS_GPT_CRASH_REASON
 from thunder.core.options import CACHE_OPTIONS
 import thunder.core.prims as prims
 from thunder import pytorch_executor, nvfuser_executor
@@ -585,6 +585,7 @@ def h(d, c):
     assert args_names == ("a", "b", "c", "d")
 
 
+@pytest.mark.skipif(IS_WINDOWS, reason=WINDOWS_GPT_CRASH_REASON)
 def test_litgpt():
     from thunder.benchmarks import LitGPTBenchmark
     from thunder.tests.litgpt_model import Config
@@ -665,6 +666,7 @@ def test_nanogpt_mlp():
     assert_close(result, module(*args, **kwargs))
 
 
+@pytest.mark.skipif(IS_WINDOWS, reason=WINDOWS_GPT_CRASH_REASON)
 def test_nanogpt():
     from thunder.benchmarks import NanoGPTBenchmark, NanoGPTConfig, _nanogpt_configs