profiling performance of an erlang application with eprof

Sometimes it's hard to pinpoint performance problems. In this cases profiling tools come handy. One of the profiling tools in Erlang is called eprof. Here is a simple example how to profile your erlang application with eprof.
First of all, you need to find which pid (module) to profile. You can use "nregs()." command to find your application's pid number in erl shell. In my case pid number is "<0.34.0>".
After finding the pid number start eprof module:

eprof:start().

now tell eprof to start profiling your application by giving the pid number.

eprof:start_profiling([pid(0,34,0)]).

note here that I have changed the dot in pid number to commas.

now wait sometime for eprof to collect some data or did something where you think the application was responding slow or stalling the cpu or whatever.

now stop profiling.

eprof:stop_profiling().

ok now we can see which functions was occupying our cpu with following command:

eprof:total_analyse().


Here is some screen output for total_analyse from my case:
6> eprof:total_analyse().
FUNCTION CALLS TIME
file:file_name_1/1 3450 13 %
erlang:port_control/3 250 7 %
prim_inet:enc_opts/2 300 5 %
erlang:port_command/2 50 4 %
erlang:port_close/1 50 4 %
prim_inet:enc_opt_val/4 300 3 %
gen:wait_resp_mon/3 200 3 %
filename:do_flatten/2 650 3 %
gen:do_call/4 200 2 %
prim_inet:dec_opt_val/3 300 2 %

if you like to see results for process by process use "analyse()" instead of "total_analyse()"
Also,It's possible to log these results to file by eprof's "log" function.