[erlang-questions] why is gen_tcp:send slow?

Rapsey <>
Thu Jun 19 10:55:22 CEST 2008

I have a streaming server written in Erlang. When it was pushing 200-300
mb/s the CPU was getting completely hammered. I traced the problem to
So instead of sending every audio/video packet with a single gen_tcp:send
call, I buffer 3 packets and then send them all at once. CPU consumption
dropped dramatically.
On one of the servers I have a simple proxy, the main process that sends
packets between the client and some other server looks like this:

transmit_loop({tcp, Sock, Data}, P) when P#transdat.client == Sock ->
    gen_tcp:send(P#transdat.server, Data),
    inet:setopts(P#transdat.client, [{active, once}]),
    {ok, P};
transmit_loop({tcp, Sock, Data}, P) when P#transdat.server == Sock ->
    gen_tcp:send(P#transdat.client, Data),
    inet:setopts(P#transdat.server, [{active, once}]),
    {ok, P};
transmit_loop({start, ServerPort}, P) ->
    {ok, Sock} = gen_tcp:connect("", ServerPort, [binary, {active,
once}, {packet, 0}]),
    {ok, P#transdat{server = Sock}};
transmit_loop({tcp_closed, _}, _) ->

The proxy is eating more CPU time than the streaming server.
Is this normal behavior? The server is running  OSX 10.4

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