bug#63986: Julia is very slow

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

>mer. 21 juin 2023 at 22:39, Cayetano Santos <csantosb@inventati.org> wrote:

>>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.

To complete my previous comment, I just realised that

  Base.USE_BLAS64

gives "true" when running fast. Guix julia gives "false".

C.