Bad default number of BLAS threads on 1.9?

[KristofferC]

Something looks strange with the number of BLAS threads on 1.9, I think.

julia> VERSION
v"1.9.0-beta2"

julia> LinearAlgebra.BLAS.get_num_threads()
1

julia> VERSION
v"1.8.4"

julia> LinearAlgebra.BLAS.get_num_threads()
8

This should just be with everything default.

cc @staticfloat

[KristofferC]

Seems to be JuliaLang/julia#46844. I don't really understand how that was supposed to work. If we set ENV["OPENBLAS_NUM_THREADS"] = "1" then LinearAlgebra.__init__() will not set the number of threads:

https://github.com/JuliaLang/julia/blob/516b097bd705faf628a3346c39279a595ab633d3/stdlib/LinearAlgebra/src/LinearAlgebra.jl#L642-L648

The reason 1.8 is still ok is because OpenBLAS_jll is not in the sysimage on 1.8 (but it is on 1.9).

OPENBLAS_DEFAULT_NUM_THREADS was added in OpenMathLib/OpenBLAS#3773 with a reference to JuliaLang/julia#46844 but it isn't used here. Maybe just a typo?