Hi,
(Disclaimer: this behaviour might have changed, haven't really checked
it in the current release but anyway ...)
I had the same experience regarding loop performance in C vs. Hipe
erlang and decided to look in to it about a year ago.
It looked like hipe did a very good job generating code for the body
of the function, but did no optimization for
recursive calls (i.e. loops). It handled it as any other call.
After each execution of the "body" hipe called runtime functions to
allow housekeeping and scheduling.
Unfortunately most functions in erlang are very small and the setup
overhead for each body call was significant resulting in very small
perfomance gains (but still some).
Compare this with an tight optimized (unrolled|coiled|pipelined) loop
in C doing condition checking on a register flag.
This is a bit unfortunate since performance bottlenecks can usually be
tracked down a few inner loops for almost any given system...
/Per
> Hello,
>
> We were wondering with Thierry Mallard about the impact of native
compilation.
> We tried to compare a big amount of floating point operations (100
millions).
> The result is greatly improved over standard Erlang.
> The result is also far from the C execution time.
>
> We were wondering why the result was different. Is there many more
operations
> implied by Erlang ?
>
> The test are at the bottom of this email.
>
> I have not yet tested the same example with ETOS. Does someone know
the
> expected impact with ETOS ?
>
> Thank you for you help.
>
> --
> Mickaël Rémond
>
>
> -=-=-=-=-=-
> Erlang test:
>
> Erlang (BEAM) emulator version 2002.09.05 [source] [hipe]
[threads:0]
>
> Eshell V2002.09.05 (abort with ^G)
> 1> c(test2, [native, {hipe, [o3]}]).
> {ok,test2}
> 2> test2:run().
> {5820686,ok}
> ======= >Means 5.8 seconds.
> -=-=-=-=-=-
> [mremond@REDACTED test]$ g++ -O3 -o testmulti testmulti.cpp
> [mremond@REDACTED test]$ ./testmulti
> 0.27user 0.00system 0:00.89elapsed 30%CPU (0avgtext+0avgdata
0maxresident)k
> 0inputs+0outputs (129major+34minor)pagefaults 0swaps
> ======= >Means less than 1 second.
>
=========================================================
Per Bergqvist
Synapse Systems AB
Phone: +46 709 686 685
Email: per@REDACTED