testing python multiprocessing: low speed because of overhead?

Question

I\'m trying to learn about multiprocessing in python (2.7). My CPU has 4 cores. In the following code I test speed of parallel Vs serial execution of the same b

Answer 1

Yes, this may be related to overhead, including:

• Creating and starting the processes
• passing the function and the arguments over to them
• waiting for process termination

If you truly have 4 physical cores on your machine (and not 2 cores with hyperthreading or similar), you should see that the ratio becomes closer to what is expected for larger inputs, as chepner said. If you only have 2 physical cores, you can't get ratio < 0.5