bug#63986: Julia is very slow

[Cayetano Santos via Bug reports for GNU Guix <bug-guix@gnu.org>]

>mer. 21 juin 2023 at 16:36, Ludovic Courtès <ludovic.courtes@inria.fr> wrote:

> Hey!
>
> The benchmark you posted, Cayetano, is:
>
>   julia -e 'using Pkg; Pkg.add("BenchmarkTools"); using BenchmarkTools; N = 1000; A = rand(N, N); B = rand(N, N); @btime $A*$B'
>
> This is a matrix multiplication that gets delegated to the underlying
> BLAS right.  Running it under ‘perf record’ confirms it:
>
> Samples: 139K of event 'cycles:u', Event count (approx.): 99624880590
> Overhead  Command      Shared Object               Symbol
>   35.27%  .julia-real  libblas.so.3.9.0            [.] dgemm_
>    3.99%  .julia-real  libjulia-internal.so.1.8    [.] gc_mark_loop
>    2.60%  .julia-real  libjulia-internal.so.1.8    [.] apply_cl
>    1.06%  .julia-real  libjulia-internal.so.1.8    [.] jl_get_binding_
>
> We’re using libblas.so (presumably from the ‘lapack’ package) and not
> OpenBLAS, so no wonder it’s slow.
>
> Could it be that:
>
>          "LIBBLAS=-lopenblas"
>          "LIBBLASNAME=libopenblas"
>
> is ineffective?  I think we have a lead!

Are we following all instructions here ?

    https://docs.julialang.org/en/v1.8/devdocs/build/distributing/#Notes-on-BLAS-and-LAPACK

I’m thinking about the variables LIBLAPACK and LIBLAPACKNAME.

C.