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?