Well first note, you don’t want to use :gen_tcp.recv for the fastest speed, you probably want to use active: :once or whatever it was with async messaging back into the app (or if you don’t have to worry about reading messages fast enough then just active true). A recv is synchronous and involves even more messages, so that would be one of a few causes of slowdowns there, but the first to fix. 
The next step to optimize is that when you receive a message with active: once then you probably want to go to a full active loop until no message in X milliseconds, at which point drop back to active: once.
Though if this is a completely arbitrary ‘fast-as-possible’ test then just staying fully active receiving would be fastest.
