The GIL is per interpreter/process, so this wouldn't be related as far as I know.

The GIL only really kicks in if you use threads in a single process. Then, the GIL will only let one single thread do actual work at a time, and will trade off which thread gets to do work. The other threads can wait on IO stuff (web requests, the file system, etc) but they can't do number crunching or data processing at the same time.

That's a really interesting observation though, I wonder what _is_ causing your separate processes to sync up?