rdtsc in Windows and Linux

Code in Windows, you have to compile it by VC++

#include <intrin.h>
unsigned __int64 rdtsc()
{
  return __rdtsc();
}

Code in Linux 

#include <stdint.h>
#include <stdio.h>

  __inline__ uint64_t rdtsc() {
    uint32_t lo, hi;
    __asm__ __volatile__ (      // serialize
    "xorl %%eax,%%eax \n        cpuid"
    ::: "%rax", "%rbx", "%rcx", "%rdx");
    /* We cannot use "=A", since this would use %rax on x86_64 */
    __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
    return (uint64_t)hi << 32 | lo;
  }
int main()
{
    printf("rdtsc is: %llu\n",rdtsc());
    return 1;
}

more detailed information: http://en.wikipedia.org/wiki/Time_Stamp_Counter

Another version in Linux:
/************ Record TSC to SMRAM offset 0xA9000 ****************/
movl $0xA9000, %ebx
rdtsc
movl %eax, (%ebx)
movl %edx, 4(%ebx)

unsigned int lo = *(unsigned int*)(0xA9000);
unsigned int hi = *(unsigned int*)(0xA9004);
unsigned long long beforeConfig = (unsigned long long)hi << 32 | lo;