As an aside, chunksize is an easily-set integer arg to Python's pool function.Anything > 1 slows my app down, simply because the cycles performed in a typical large-job worker loop (into the billions) far exceed the frequency at which the loop returns a result, which is once, at the end.The problem I've got is while multi loops run fast, they tend to slow over time to about 50% of their startup speed. The end result is 4 cores vs. 1 cuts job time only ~50% vs. the expected 75% at job start.