bug#63986: Julia is very slow

[Ludovic Courtès]

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:

--8<---------------cut here---------------start------------->8---
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_
--8<---------------cut here---------------end--------------->8---

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!

Ludo’.