Memory allocation nano-benchmark.

[Christian Szegedy <szegedy@or.uni-bonn.de>]

Let us look at another example where ocaml not really shines:

mem.ml:

let test tablesize =
   let table =
     Array.init tablesize (fun i ->
       Array.init tablesize (fun j ->
         Array.init tablesize (fun k ->
           ((i+1)*(j+1)*(k+1))))) in ()

let _ = test (int_of_string Sys.argv.(1))


mem.c:

void test(int tablesize)
{

    int i;
    int ***table = (int ***)malloc(tablesize *sizeof(int **));

    for( i=0; i<tablesize ; i++ )
    {
       int j;
       table[i] = (int **)malloc(tablesize * sizeof(int *));

       for ( j=0 ; j < tablesize ; j++ )
       {
          int k;
          table[i][j] = (int *)malloc(tablesize * sizeof(int));

          for ( k =0 ; k < tablesize ; k++ )
          {
             table[i][j][k] = (i+1)*(j+1)*(k+1);
          }
       }
    }
}


int main(int argc,char *argv[])
{
    int i;

    if( argc < 2 ) { return -1; }

    test(atoi(argv[1]));

    return 0;
}

On an old sub-Ghz Pentium laptop:

ocamlopt -unsafe -inline 40 mem.ml
time a.out 500
real    0m4.229s
user    0m3.870s
sys     0m0.360s


gcc -O3 -fomit-frame-pointer mem.c
time a.out 300
real    0m0.935s
user    0m0.420s
sys     0m0.500s



On a new Opteron box (OK, it's cheating, becasuse OCamls ints
are 64 bits, but there is still no disk-cache involved since
it has 64gigs :)):

gcc -O3 -fomit-frame-pointer mem.c
time ./a.out 500
real    0m0.803s
user    0m0.224s
sys     0m0.575s


ocamlopt -unsafe -inline 40 mem.ml
time ./a.out 500
real    0m8.651s
user    0m7.270s
sys     0m1.357s