So, it wasn't actually synchonrizing all of the I/Os onto one thread, but I wasn't getting any parallelism due to the amount of time required to dispatch I/Os.

So, it wasn't actually synchonrizing all of the I/Os onto one thread, but I wasn't getting any parallelism due to the amount of time required to dispatch I/Os. Essentially, my program was highly concurrent, but I wasn't able to get any I/O parallelism because each syscall was pretty cheap, and the cost of dispatching each I/O was too expensive.