#include <dirent.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>

int
main (void)
{
#define N 100
  unsigned long long t0;
  unsigned a,d;
  asm volatile ("rdtsc" : "=a" (a), "=d" (d));
  t0 = (((unsigned long long) d) << 32) + a;
  int i;
  for (i = 0; i < N; ++i)
    {
     char buf[100000];
      int fd = open ("/proc/cpuinfo", O_RDONLY);
      read(fd,buf,sizeof(buf));
      close (fd);
    }
  unsigned long long tn;
  asm volatile ("rdtsc" : "=a" (a), "=d" (d));
  tn = (((unsigned long long) d) << 32) + a;
  printf ("cpuinfo %llu cycles for %d accesses\n", tn - t0, N);

  asm volatile ("rdtsc" : "=a" (a), "=d" (d));
  t0 = (((unsigned long long) d) << 32) + a;
  for (i = 0; i < N; ++i)
    {
      DIR *d = opendir ("/sys/devices/system/cpu");
      while (readdir (d))
        ;
      closedir (d);
    }
  asm volatile ("rdtsc" : "=a" (a), "=d" (d));
  tn = (((unsigned long long) d) << 32) + a;
  printf ("readdir /sys %llu cycles for %d accesses\n", tn - t0, N);

  asm volatile ("rdtsc" : "=a" (a), "=d" (d));
  t0 = (((unsigned long long) d) << 32) + a;
  for (i = 0; i < N; ++i)
    {
      struct stat64 st;
      stat64 ("/sys/devices/system/cpu", &st);
    }
  asm volatile ("rdtsc" : "=a" (a), "=d" (d));
  tn = (((unsigned long long) d) << 32) + a;
  printf ("stat /sys %llu cycles for %d accesses\n", tn - t0, N);

  return 0;
}