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CI: Windows on ARM experiment: OpenBLAS routines (not for merging) - #1006

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a90-winarm-routines
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bashtage wants to merge 4 commits into
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a90-winarm-routines

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@bashtage bashtage commented Nov 4, 2026 •

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Experimental, not for merging. One of four experiments on the access violations in numpy.linalg on Windows on ARM that #1003 found. With OPENBLAS_NUM_THREADS=1, inv and solve of small positive definite matrices crash in numpy 2.5.4's OpenBLAS, and numpy alone reproduces it. Each experiment has its own pull request, so that they run at the same time and each can change without restarting the others: #1003 (arch's tests), #1004 (the calls and threads), #1005 (the numpy versions), #1006 (the OpenBLAS routines) and #1007 (SciPy, the stack and faulthandler).

Like #1003, this removes the Azure pipeline (azure-pipelines.yml) and the wheel builds (cron-test.yml), so that no tests run here. arch is not built: the job installs only numpy (and SciPy where needed) from wheels.

What this one runs

The LAPACK and BLAS routines in numpy's own OpenBLAS, called directly with ctypes: getrf, getrs, gesv, getri, potrf, trsm, laswp, gemm and gemv. inv is gesv (getrf, then laswp and trsm in getrs), so this finds the routine that crashes. getrs, getri, trsm and laswp get an LU computed without BLAS, so a crash in getrf can't be blamed on them. Each call checks its result without BLAS. ctypes turns an access violation into an OSError with the address, which the report shows.

The jobs also set the number of threads at run time with openblas_set_num_threads, to find whether the crash follows the number when OpenBLAS starts or when it is called: OPENBLAS_NUM_THREADS 1, 4 and unset, unset then set to 1, 4 then set to 1, and 1 then set to 4. numpy's inv and solve run too, to compare with. numpy 2.5.4, Python 3.14.

How it works

ci/github-actions/winarm_blas.py, the same in all four pull requests, makes every call in a child process. A child walks through the sizes (1 to 64, then every 8th to 160) and prints start CALL N before each call. When it crashes or hangs (60 s), the size is recorded and a new child goes on with the next size. Each size that crashed is then tried alone, in a new process. So a map takes minutes rather than a process for every size, which is what made the size map in #1003 so slow. The matrices are built without BLAS (einsum), so the call under test is the only BLAS call.

The job passes when the map is complete, whether or not anything crashed. The results are in the job summary, in the log as they come, and in the report.md artifact. Each report starts with the builds and what OpenBLAS reports at run time (kernel, threads, configuration) and the CPU.

Checked locally (x64)

  • actionlint and check-jsonschema (GitHub workflow schema) report no problems. The script is clean under ruff, black, isort, flake8, bandit and pylint.
  • Every command of the four workflows runs to the end on x64, in under a minute in total, with no crashes. selftest crashes at size 5 and is found, the walk goes on, and the crash is found again alone.
  • The ctypes calls into numpy's OpenBLAS (ILP64 on x64) and SciPy's (LP64) check their results without BLAS.

🤖 Generated with Claude Code

The experiments on the numpy.linalg crashes on Windows on ARM (see #1003)
run in their own pull requests. Remove the Azure pipeline and the wheel
builds, the workflows that run the tests, so that these pull requests do
not use the CI queues. Not for merging.
Maps the sizes at which numpy.linalg calls, SciPy's LAPACK and BLAS, and
the LAPACK and BLAS routines of numpy's OpenBLAS (called directly with
ctypes) crash. A child process walks through the sizes, and after a crash
or a hang a new child continues with the next size, so a map takes
minutes rather than a process for every size. Each size that crashed is
then tried alone. Options set the OpenBLAS threads in the environment or
at run time, the stack of the thread that makes the calls, and
faulthandler. Not for merging.
Calls getrf, getrs, gesv, getri, potrf, trsm, laswp, gemm and gemv in
numpy's OpenBLAS directly, with the number of threads set when OpenBLAS
starts and changed at run time. Not for merging.

result["scipy"] = scipy.__version__
result["scipy openblas"] = runtime("scipy")
except ImportError:
dgesv crashes at sizes 23 to 31 with 1 thread, but dgetrf and dgetrs,
which dgesv calls inside, do not crash alone. Call them one after the
other on the same matrix, as dgesv does, and call dgesv with three
right-hand sides. Not for merging.
@bashtage bashtage closed this Nov 5, 2026
@bashtage
bashtage deleted the a90-winarm-routines branch November 11, 2026 13:39
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