Python's default interpreter can run a single thread per virtual core due to Global Interpreter Lock implementation. This code demonstrates CPU usage while running a busy wait function using 8 threads and 8 processes.
Tests are run on an system with i5 processor (i5-4250U), which has 2 cores and 4 virtual cores (hyperthreading?). Output below indicates interpreter does not employ second physical core when using threads. But when using processes both cores are working with 100% utilization.
before starting threads (idle)
[4.9, 3.0, 2.1, 2.0]
[3.1, 6.0, 3.1, 5.9]
[5.0, 3.0, 3.0, 5.9]
[6.9, 4.0, 2.0, 6.9]
[5.9, 3.0, 7.0, 2.0]
[8.0, 5.9, 3.0, 2.0]
[7.0, 4.0, 2.1, 2.0]
[5.9, 4.0, 3.1, 2.0]
[8.0, 5.1, 4.0, 2.0]
[2.0, 3.0, 5.0, 2.9]
starting threads
done
threads running
[61.4, 62.1, 53.6, 55.2]
[59.8, 59.5, 56.5, 58.1]
[60.2, 59.1, 56.0, 53.4]
[58.8, 60.4, 54.0, 55.7]
[65.3, 58.8, 56.7, 57.8]
[60.2, 62.4, 58.0, 56.7]
[63.3, 60.4, 55.1, 54.1]
[59.8, 59.3, 56.0, 55.6]
[62.2, 61.8, 55.7, 54.0]
[58.8, 60.4, 54.0, 57.9]
after threads stopped (idle)
[6.9, 4.0, 2.0, 3.0]
[5.0, 5.0, 0.0, 5.0]
[4.0, 5.0, 2.0, 3.0]
[2.0, 4.0, 1.0, 4.0]
[3.0, 6.8, 3.0, 5.0]
[5.9, 8.0, 3.1, 4.9]
[7.0, 3.0, 2.0, 4.9]
[7.9, 3.0, 2.0, 2.0]
[2.0, 4.0, 2.0, 4.9]
[5.9, 5.0, 5.2, 4.0]
starting processes
done
processes running
[100.0, 100.0, 100.0, 100.0]
[100.0, 100.0, 100.0, 100.0]
[100.0, 100.0, 100.0, 100.0]
[100.0, 100.0, 100.0, 100.0]
[100.0, 100.0, 100.0, 100.0]
[100.0, 100.0, 100.0, 100.0]
[100.0, 100.0, 100.0, 100.0]
[100.0, 100.0, 100.0, 100.0]
[100.0, 100.0, 100.0, 100.0]
[100.0, 100.0, 100.0, 100.0]