[erlang-questions] ring benchmark results: Is Erlang crazy fast?

[Ulf Wiger]

You must also wait for the message to pass through
the entire ring.

BR,
Ulf W

2007/7/21, David Cabana <dcabana@REDACTED>:
> Joe Armstrong proposed an exercise in Programming Erlang :
> "Write a ring benchmark. Create N processes in a ring. Send a message
> round the ring M times. So that a total of N * M messages get sent.
> Time how long this takes for different values of N and M."
>
> I did so, but I am having a hard time accepting the results. I am
> running latest the DarwinPorts build of Eralang on a G4 PowerBook.
> I'll post results, my reservations, and source code in that order.
>
> %% --- results, pasted from console session
> Erlang (BEAM) emulator version 5.5.5 [source] [async-threads:0]
> [hipe] [kernel-poll:false]
>
> Eshell V5.5.5  (abort with ^G)
> 1> c(ring).
> {ok,ring}
> 2> ring:start(5000,10).
> Total time=10 (32) milliseconds
> ok
> 3> ring:start(5000,10000).
> Total time=20 (26) milliseconds
> ok
> 4> ring:start(5000,10000000).
> Total time=10 (36) milliseconds
>
> I find it hard to believe Erlang can send 5*10^10 messages in .036
> seconds on my hardware.  Can anyone give me a sanity check here?
>
> Here's the code.  I left in some (commented out) diagnostic code;
> using it with small values of M and N leads me to think the program
> is doing what it is supposed to do. I am an Erlang newb; this is the
> longest and least trivial Erlang program I've written. Any
> observations on better style would be welcome.
>
>
> -module(ring).
> -export([start/2, foo/1, bar/0]).
> %%
> %% per Armstrong's "Programming Erlang"
> %% Write a ring benchmark. Create N processes in a ring. Send a
> message round the ring M times.
> %% So that a total of N * M messages get sent. Time how long this
> takes for different values of N and M.
> %%
>
> foo(Next) ->
>      receive        %% foo does not care about the value of 2nd
> element in {x,y}, only bar does
>         {0, Any} ->
>             % io:format("foo done ~n",[]),
>             Next ! {0, Any};    %% send the 0 along to tell everyone to shut down
>         {N, Any} ->
>             % io:format("  foo ~p  ~n", [N]),
>             Next ! {N-1, Any},
>             foo(Next);
>         Other -> io:format("foo: huh? ~p ~n", [Other])
>      end.
>
> bar() ->
>      receive
>         {0, Next} ->
>             % io:format("bar done ~n",[]),
>             Next ! {0, Next};
>         {N, Next} ->
>             % io:format("bar ~p  ~n", [N]),
>             Next ! {N-1, Next},
>             bar();
>         Other -> io:format("bar: huh? ~p ~n", [Other])
>      end.
>
> %% construct a chain of processes
> %% process J-1 routes msgs to process J for all J < K
> chain(0, Pid) -> Pid;
> chain(K, Pid) -> chain(K-1, spawn(ring,foo,[Pid])).
>
> %% N is the number of processes in the ring
> %% M is the number of times msgs circle the ring
> start(N, M) ->
>      statistics(runtime),
>      statistics(wall_clock),
>
>      A= spawn(ring, bar, []),
>      B= chain(N-1, A),
>      A ! {N*M, B},
>
>      {_, RT} = statistics(runtime),
>      {_, WC} = statistics(wall_clock),
>      io:format("Total time=~p (~p) milliseconds~n", [RT, WC]).
>
>
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