There are tiers for performance. A few hundred (or thousand) ops/sec -- a GIL isn't going to hurt too much. A few thousand -- well-designed IPC is fine. A few tens of thousands -- lock-free gets important. Hundreds of thousands (or millions) -- userspace/kernel transitions and interrupt servicing can dominate, and an application's interactions with the OS need to be very carefully managed...

It all depends on how much you want to get out of your hardware.