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Use max(1, Sys.CPU_THREADS) BLAS threads for aarch64. #46085

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Jul 20, 2022
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Use max(1, Sys.CPU_THREADS) BLAS threads for aarch64. #46085

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aa27862
Use `max(1, Sys.CPU_THREADS)` BLAS threads for `aarch64`.
chriselrod Jul 18, 2022
2b33c6b
Update LinearAlgebra.jl
chriselrod Jul 18, 2022
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6 changes: 5 additions & 1 deletion stdlib/LinearAlgebra/src/LinearAlgebra.jl
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Expand Up @@ -582,7 +582,11 @@ function __init__()
Base.at_disable_library_threading(() -> BLAS.set_num_threads(1))

if !haskey(ENV, "OPENBLAS_NUM_THREADS")
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Wait, this should look at GOTO_NUM_THREADS AND OMP_NUM_THREADS as well: https://github.com/xianyi/OpenBLAS/blob/c43ec53bdd00d9423fc609d7b7ecb35e7bf41b85/README.md#setting-the-number-of-threads-using-environment-variables

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GOTO_NUM_THREADS comes from the original GOTOBLAS library. Nobody should be using it!

For OMP, I thought that only applies if you build with OpenMP for threading - which we don't. I think we should only look at OPENBLAS_NUM_THREADS.

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As a matter of fact OpenBLAS respects those variables. If you set them you can see with BLAS.get_num_threads that OpenBLAS changes the setting accordingly

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@ViralBShah ViralBShah Jul 21, 2022 •
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Yup it does. I was just saying that we may only want to use one of them and only document that. However, I don't have a strong opinion if we want to use the other ones - but what should we do if more than one of those environment variables are present?

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If any of those variables is set, we shouldn't override it. See #46118 🙂

BLAS.set_num_threads(max(1, Sys.CPU_THREADS ÷ 2))
@static if Sys.isapple() && Base.BinaryPlatforms.arch(Base.BinaryPlatforms.HostPlatform()) == "aarch64"
BLAS.set_num_threads(max(1, Sys.CPU_THREADS))
else
BLAS.set_num_threads(max(1, Sys.CPU_THREADS ÷ 2))
end
end
end

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