Some of the computational tasks performed in scqubits can benefit significantly from parallelization. The scqubits package leverages parallel-processing capabilities provided by the Python Standard Library
multiprocessing module. For better pickling support, scqubits further supports use of
One important consideration for parallelization of tasks like parameter sweeps is the fact that Numpy and Scipy tend to make use of multi-threading internally. (Details of that will depend on how they were built on the machine in question.) This will generally lead to competition between multi-threading on the Numpy/Scipy level and parallelization of
map methods via
In many cases, best performance is obtained by limiting the number of threads used by Numpy to “a few”. (Precise numbers will be machine dependent and need to be determined on a case by case basis.) Limiting this thread number can be achieved from within a Python script or Jupyter and is accomplished by setting environment variables.
Limiting the number of threads will only be effective if environment variables are set before the first import of Numpy.
Several environment variables can play a role, and which one is needed may again be machine-dependent. We thus simply set them all:
import os NUM_THREADS = "1" os.environ["OMP_NUM_THREADS"] = NUM_THREADS os.environ["OPENBLAS_NUM_THREADS"] = NUM_THREADS os.environ["MKL_NUM_THREADS"] = NUM_THREADS os.environ["VECLIB_MAXIMUM_THREADS"] = NUM_THREADS os.environ["NUMEXPR_NUM_THREADS"] = NUM_THREADS
At this point, Numpy import and import of scqubits can proceed.
import numpy as np import scqubits from scqubits import HilbertSpace, InteractionTerm, ParameterSweep
Enabling parallel processing¶
Parallel processing is enabled for appropriate scqubits methods and classes by passing the number of cores to be used through the keyword argument
num_cpus. The following classes and class methods support parallelization:
Classes and class methods supporting parallelization¶
Class or class method
To use parallelization, the keyword argument
num_cpus must be passed, specifying the number of cores to be used as an integer, e.g.
sweep = ParameterSweep( param_name=param_name, ..., ..., num_cpus=4 )
num_cpus exceeds the value 1 when passed, scqubits starts a parallel processing pool of the desired number of processes.
Global num_cpus default¶
The global default for
num_cpus is stored in
scqubits.settings.NUM_CPUS. Upon import of scqubits, that constant has the value
1 (no parallelization). To change this default and use a user-defined core number by default (say 6), set
scqubits.settings.NUM_CPUS = 6
multiprocessing vs. pathos¶
scqubits supports parallelization through
multiprocessing as well as
pathos. The latter is the default option and is more robust thanks to the advanced pickling methods enabled through
To switch from use of
multiprocessing, simply alter the following setting:
scqubits.settings.MULTIPROC = 'multiprocessing'