static inline uint64_t rdtscp()
{
  uint64_t tsc;


  __asm__ __volatile__(
    "rdtscp;"
    "shl $32, %%rdx;"
    "or %%rdx,%%rax"
    : "=a" (tsc)
    :
    : "%rcx", "%rdx", "memory"
  );

  return tsc;
}