From: George Ogata <g_ogata@...>
Date: 2004-08-28T03:55:33+09:00
Subject: Re: performance comparison

Boris Glawe <boris@boris-glawe.de> writes:

> What's the reason for this big performance difference ?

I don't know what your C code looks like, but when you consider what
must go in a typical C statement vs. an equivalent ruby statement, I
don't find it too surprising.  How do other interpreted languages
(e.g., python) go?

As a simpler example, observe a dumb-Fibonacci:

----- sources ----

g@crash:~/tmp$ #### C version ####
g@crash:~/tmp$ cat test.c
#include <stdio.h>

int fib(int n) {
  switch (n) {
  case 0:
    return 0;
  case 1:
    return 1;
  default:
    return fib(n-1) + fib(n-2);
  }
}

int main(int argc, char **argv) {
  int n;
  sscanf(argv[1], "%d", &n);
  printf("%d\n", fib(n));
  return 0;
}
g@crash:~/tmp$ #### ruby version ####
g@crash:~/tmp$ cat test.rb
def fib n
  if n > 1
    fib(n-1) + fib(n-2)
  elsif n.zero?
    0
  else
    1
  end
end

puts fib(ARGV[0].to_i)
g@crash:~/tmp$ #### python version ####
g@crash:~/tmp$ cat test.py
import sys

def fib(n):
    if n > 1:
        return fib(n-1) + fib(n-2)
    elif n == 0:
        return 0
    else:
        return 1

print fib(int(sys.argv[1]))

----- runs -----

g@crash:~/tmp$ gcc test.c && /usr/bin/time ./a.out 35
9227465
0.44user 0.00system 0:00.44elapsed 100%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (100major+13minor)pagefaults 0swaps
g@crash:~/tmp$ /usr/bin/time ruby test.rb 35
9227465
22.95user 0.07system 0:23.02elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (243major+168minor)pagefaults 0swaps
g@crash:~/tmp$ /usr/bin/time python test.py 35
9227465
17.24user 0.00system 0:17.30elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (370major+250minor)pagefaults 0swaps

That's about 52x longer for ruby.  Not as big a coefficient as your
program, but the difference between the implementations (in terms of
complexity of the expressions evaluated) in my example is probably
much less than in yours due to the simplicity of the programs.  Again,
this is highly dependant on what your C version looks like.

HTH.