python - Limit number of threads in numpy

Question

It seems that my numpy library is using 4 threads, and setting OMP_NUM_THREADS=1 does not stop this.

numpy.show_config() gives me these results:

atlas_threads_info:
    libraries = ['lapack', 'ptf77blas', 'ptcblas', 'atlas']
    library_dirs = ['/usr/lib64/atlas']
    define_macros = [('ATLAS_INFO', '""3.8.4""')]
    language = f77
    include_dirs = ['/usr/include']
blas_opt_info:
    libraries = ['ptf77blas', 'ptcblas', 'atlas']
    library_dirs = ['/usr/lib64/atlas']
    define_macros = [('ATLAS_INFO', '""3.8.4""')]
    language = c
    include_dirs = ['/usr/include']
atlas_blas_threads_info:
    libraries = ['ptf77blas', 'ptcblas', 'atlas']
    library_dirs = ['/usr/lib64/atlas']
    define_macros = [('ATLAS_INFO', '""3.8.4""')]
    language = c
    include_dirs = ['/usr/include']
openblas_info:
  NOT AVAILABLE
lapack_opt_info:
    libraries = ['lapack', 'ptf77blas', 'ptcblas', 'atlas']
    library_dirs = ['/usr/lib64/atlas']
    define_macros = [('ATLAS_INFO', '""3.8.4""')]
    language = f77
    include_dirs = ['/usr/include']

So I know it is using blas, but I can't figure out how to make it use 1 thread for matrix multiplication.

Answer 1

Try setting all of the following:

export MKL_NUM_THREADS=1
export NUMEXPR_NUM_THREADS=1
export OMP_NUM_THREADS=1

Sometimes it's a bit tricky to see where exactly multithreading is introduced.