How do I limit the nr of processors/threads/...?

[GenieTim]

I have tried with the following environment variables:

keys = [
 "OMP_NUM_THREADS",
 "MKL_NUM_THREADS",
 "NUMEXPR_NUM_THREADS",
 "OPENBLAS_NUM_THREADS",
 "VECLIB_MAXIMUM_THREADS",
 ]
for key in keys:
 my_env[key] = str(num_procs)
 os.environ[key] = str(num_procs)

but apparently, none of them actually limits the nr of procs spawned by dpnp. What am I missing, how can I limit them to investigate performance effects?