QueryPerformanceFrequency,RDTSC,CPU频率

//warning C4035: 'RDTSC' : no return value
#pragma warning(disable:4035)
 
#include <Windows.h>
 
//RDTSC-Read Time-Stamp Counter
//自开机以来CPU经历的时钟周期数
unsigned __int64 RDTSC()
{
    __asm _emit 0x0F;
    __asm _emit 0x31;
}
 
//CPU的频率
double CpuFrequency()
{
    //On a multiprocessor machine, it should not matter which processor is called.
    //However, you can get different results on different processors due to bugs in
    //the BIOS or the HAL. To specify processor affinity for a thread, use the SetThreadAffinityMask function.
    HANDLE hThread=GetCurrentThread();
    SetThreadAffinityMask(hThread,0x1);  
   
    //主板上高精度定时器的晶振频率
    //这个定时器应该就是一片8253或者8254
    //在intel ich7中集成了8254
    LARGE_INTEGER lFrequency;
    QueryPerformanceFrequency(&lFrequency);
    //printf("高精度定时器的晶振频率：%1.0fHz.\n",(double)lFrequency.QuadPart);
 
    //这个定时器每经过一个时钟周期，其计数器会+1
    LARGE_INTEGER lPerformanceCount_Start;
    QueryPerformanceCounter(&lPerformanceCount_Start);
 
    //RDTSC指令:获取CPU经历的时钟周期数
    __int64 _i64StartCpuCounter=RDTSC();
 
    //延时长一点,误差会小一点
    //int nTemp=100000;
    //while (--nTemp);
    Sleep(200); 
 
    LARGE_INTEGER lPerformanceCount_End;
    QueryPerformanceCounter(&lPerformanceCount_End);
 
    __int64 _i64EndCpuCounter=RDTSC();
 
    //f=1/T => f=计数次数/(计数次数*T)
    //这里的“计数次数*T”就是时间差
    double fTime=((double)lPerformanceCount_End.QuadPart-(double)lPerformanceCount_Start.QuadPart)
        /(double)lFrequency.QuadPart;
 
    return (_i64EndCpuCounter-_i64StartCpuCounter)/fTime;
}
 
int main(int argc, char* argv[])
{
    printf("CPU频率为:%1.6fMHz.\n",CpuFrequency()/1000000.0);
    return 0;
}