Any suggestion on setting MKL_NUM_THREADS environment variable?

[makecent]

I always receive a warning massage about MKL_NUM_THREADS as below:

mmaction/utils/setup_env.py:42: UserWarning: Setting MKL_NUM_THREADS environment variable for each process to be 1 in default, to avoid your system being overloaded, please further tune the variable for optimal performance in your application as needed.

I wonder if this variable affect much, and if it does, how should I find a good one excpet random searching?