Nono, quite the opposite. Out of order queues are not yet supported - each set of things you want to be able to execute without dependencies on each other need to be in a separate queue.
You need one queue per device, and you need to flush the queues for all devices before you wait on any queues. Waiting on one queue will block the calling thread and you will not get a chance to request that the second queue start executing. If you flush both then both can start in the background and only then do you wait on one or both.