BUG: spatial: long hangs using Qhull in SciPy 1.13.0, in Colour CI about scipy HOT 13 OPEN

hmm, nothing obvious sticks out to me in the git history. Maybe gh-20337 @ev-br ?

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Maybe gh-20337?

No way it can explain the runtime change from 15min to 4 hrs.

Something else must have changed. I'd first verify the "new" run time is stable, then try to replicate locally. Then bisect.

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Confirming it is coming from 1.13.0, I banned the version and did a fresh build in ~15mins using 1.12.0: https://github.com/colour-science/colour/actions/runs/8890511725/job/24410682802

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1. Do you see it on other platforms, or can you confirm it's windows specific?

2. Can you reproduce this locally?

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Hey @ev-br,

It is Windows only and I cannot reproduce locally as I'm developing on macOs.

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Just to confirm: with scipy 1.13 the Windows CI run takes 4hrs and MacOS and Linux runs take 15 mins, correct?

Also, with scipy 1.12, all of them are 15 mins?

It's likely much faster to debug in a Windows VM. If only to see if the issue is specific to the GH runners or windows in general.

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Correct yes!

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Is this a wheel install or you are building it yourself in the CI?

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It is a wheel install, Scipy is one of our dependencies.

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Right. To clarify, the installation is fast, but the test suite takes 4 hours.

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There was a substantial bump in vendored OpenBLAS version between 1.12.0 and 1.13.0 of course. I suppose that's also worth considering, especially since the 0.3.26.dev version specifically addressed a concurrency issue on Windows. Having a way to bisect with a simple reproducer as Evgeni alluded to would of course be great.

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Agreed that OpenBLAS version is the prime candidate. We have nightlies that were just upgraded from 0.3.26.dev to 0.3.27, with a known regression that can cause this kind of performance regression fixed. Worth trying with those: https://anaconda.org/scientific-python-nightly-wheels/scipy

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