[eiki@dagobah /tmp]$ cat tst.c

#include <stdio.h>
#include <time.h>

#ifndef RDTSC_H_
#define RDTSC_H_

inline unsigned long long rdtsc() {
    unsigned long long ret;
    __asm__ volatile ("rdtsc" : "=A" (ret));
    return ret;
}

#endif /* RDTSC_H_ */

int main() {
 unsigned long long bef, aft, dif;
 int i, j, k;
 struct timespec ts, tsrem;
 int interval[8] = { 1, 1000, 1000000, 3000000, 4000000, 5000000 };

 k = 0;
 for(i = 0; i<10; i++) {
   printf("x=%016llx\n", rdtsc());
   for(j = 0; j<10; j++) k++;
 }
 printf("k=%6x\n", k);

  // 1-3 sec
 for(i=1; i<=3; i++) {
   printf("measuring %d sec:\n", i);
   bef = rdtsc();
   sleep(i);
   aft = rdtsc();
   dif = aft - bef;
   printf("   a=%016llx(%lld)\n   b=%016llx(%lld)\n   diff=%12lld\n",
          bef, bef, aft, aft, dif);
 }

  // 1 nsec / 1 usec / 1,3,4,5 msec
 for(i=0; i<=5; i++) {
   ts.tv_sec = 0;
   ts.tv_nsec = interval[i];
   printf("measuring %d nsec:\n", ts.tv_nsec);
   bef = rdtsc();
   nanosleep(&ts, &tsrem);
   aft = rdtsc();
   dif = aft - bef;
   printf("   a=%016llx(%lld)\n   b=%016llx(%lld)\n   diff=%12lld\n",
          bef, bef, aft, aft, dif);
 }

}

[eiki@dagobah /tmp]$ cc tst.c
[eiki@dagobah /tmp]$ ./a.exe
x=00000224fde3d7f1
x=00000224fdecf06b
x=00000224fded4b46
x=00000224fded910b
x=00000224fdf51ae4
x=00000224fdf5760d
x=00000224fdf5c2ec
x=00000224fdf7dba2
x=00000224fdf83283
x=00000224fdf87ea1
k=    64
measuring 1 sec:
   a=00000224fdfb4828(2357903181864)
   b=0000022522de77d5(2358522050517)
   diff=   618868653
measuring 2 sec:
   a=0000022522e072ca(2358522180298)
   b=000002256a6ed319(2359722693401)
   diff=  1200513103
measuring 3 sec:
   a=000002256a70a3d7(2359722812375)
   b=00000225d5be2cc4(2361523055812)
   diff=  1800243437
measuring 1 nsec:
   a=00000225d5c4a8bc(2361523480764)
   b=00000225d5d72e2d(2361524694573)
   diff=     1213809
measuring 1000 nsec:
   a=00000225d5d87678(2361524778616)
   b=00000225d5f74fed(2361526800365)
   diff=     2021749
measuring 1000000 nsec:
   a=00000225d5fad017(2361527029783)
   b=00000225d60ef16c(2361528349036)
   diff=     1319253
measuring 3000000 nsec:
   a=00000225d61023aa(2361528427434)
   b=00000225d63242da(2361530663642)
   diff=     2236208
measuring 4000000 nsec:
   a=00000225d635a36d(2361530884973)
   b=00000225d693bf1b(2361537052443)
   diff=     6167470
measuring 5000000 nsec:
   a=00000225d6951a11(2361537141265)
   b=00000225d6b3e556(2361539159382)
   diff=     2018117
[eiki@dagobah /tmp]$