linux 怎么取到纳秒计算的时间

------解决方案--------------------
clock_gettime可获得纳秒级精确 

  linux rdtsc 纳秒级计时  2011-06-30 21:30:19

分类： LINUX

 部分代码

 unsigned int ts,te;
 unsigned int sdx,edx;
 unsigned long long int clock_cycles;
 unsigned int max=1<<31;
 unsigned long long int max0=(unsigned long long int )max*2;

 __asm__ __volatile__(
 "rdtsc\n\t"
 :"=a"(ts),"=d"(sdx));

 //-------------some functions need to record time-----------//
 b

 __asm__ __volatile__(
 "rdtsc\n\t"
 :"=a"(te),"=d"(edx));


 printf("tick ax start =%u tick end=%u \n",ts, te);
 printf("tick dx start =%u tick end=%u \n",sdx, edx);
 clock_cycles=(unsigned long long)(edx-sdx)*max0 te-ts;
 //or clock_cycles=(unsigned long long)(edx-sdx)*0x0100000000l+ te-ts;
 printf("ticks=%llu\n",clock_cycles);