We run multiple Ruby processes per CPU so that when one process is waiting for the db or memcache, another can be doing useful work on the same CPU That's the

We run multiple Ruby processes per CPU so that when one process is waiting for the db or memcache, another can be doing useful work on the same CPU That's the trivial case. When waiting for the db or memcache (I/O in general), the GIL is lifted, so it doesn't get in the way. It only gets in the way if multiple threads are inside the ruby VM doing work.