First thing i noticed is that you’re calling wrk on ‘/supply-partners/mopuba’ where your icepick code has the route defined as ‘/supply-partners/mopub’ (without the trailing ‘a’) this could give you a different code handling path than you intended. At least something to try 
Have you seen this benchmark? GitHub - mroth/phoenix-showdown: 🏇 benchmark Sinatra-like web frameworks · GitHub
This one has already way higher request rates you’re getting now, maybe try that one first on the same hardware to see how it performs and use it as a baseline?
Another thing you could try is compiling with HiPe (high performance erlang) compiler through usage of ERL_COMPILER_OPTIONS="[native,{hipe, [o3]}]" when calling mix compile.
You could also try using one of the (erlang) profiling tools to see which functions take most of your CPU cycles.
One last thing i noticed when testing your stuff out on a simple macbook air 11" is that i could double the req/sec when i changed the json payload from the one above to just ‘{}’. So it seems it could have something to do with string handling of the incoming json. On the macbook air 11" i got 11k req/sec.
Goodluck!
