Here is the benchmark that I used way back to measure performance of
file descriptor allocation.  Hope it helps.

Niels.

#include <stdio.h>
#include <fcntl.h>
#include <sys/time.h>
#include <sys/resource.h>

#define NFILES	60000
#define TRIALS	10000L
 
int files[NFILES];

#define ssec ru_stime.tv_sec
#define usec ru_utime.tv_sec
#define susec ru_stime.tv_usec
#define uusec ru_utime.tv_usec

void
massage (int fd)
{
  u_long i;
  struct rusage t1, t2;

  getrusage(RUSAGE_SELF, &t1);

  for (i = 0; i < TRIALS; i++) {
    close (files[0]);
    close (files[fd]);
    files[0] = open("/etc/passwd", O_RDONLY, 0);
    if (files[0] == -1) {
      perror("massage: open(0)");
      exit (0);
    }
    files[fd] = open("/etc/passwd", O_RDONLY, 0);
    if (files[fd] == -1) {
      perror("massage: open");
      exit (0);
    }
  }
    
  getrusage(RUSAGE_SELF, &t2);

  printf ("%d %lf\n", fd, (double)(t2.ssec + t2.usec - t1.ssec - t1.usec) + 
	  (double)(t2.susec + t2.uusec - t1.susec - t1.uusec)/1000000);

}

int
main (void)
{
  int i;
	
  for (i = 0; i < NFILES; i++) {
    files[i] = open("/etc/passwd", O_RDONLY, 0);
	printf ("%d: %d\n", i, files[i]);
    if (files[i] == -1) {
      perror("open");
      exit (0);
    }
  }

  for (i = 1; i < NFILES; i += 2000)
    massage (i);

  return 1;
}