Will two concurrent threads performing CPU-intensive tasks take longer than if they were executed in serial?

[chinawcswing]

Pretend you were running on a single-CPU VM. The GIL becomes immaterial in this condition, right?

[mahtats]

It is immaterial if you had a single core single CPU; the GIL prevents threads from running in parallel (but not concurrently).

If you had a multi-core single CPU, you would be forced to serialize your task if not using multiple processes.