Open UDP socket per process and feed them with data, see how much it can hadle.
$ rebar3 release
Start server to listen to 1000 ports from 12000 to 13000
$ VMARGS_PATH="$PWD/server.args" ./_build/default/rel/udpstress/bin/udpstress foreground -extra server 12000 13000
From another shell start client to send to those ports
$ VMARGS_PATH="$PWD/client.args" ./_build/default/rel/udpstress/bin/udpstress foreground -extra client localhost 12000 13000