第一种方法利用System.DateTime.Now

static void SubTest()
{
    DateTime beforDT = System.DateTime.Now;

    //耗时巨大的代码

    DateTime afterDT = System.DateTime.Now;
    TimeSpan ts = afterDT.Subtract(beforDT);
    Console.WriteLine("DateTime总共花费{0}ms.", ts.TotalMilliseconds);
}

第二种用Stopwatch类(System.Diagnostics)

static void SubTest()
{
    Stopwatch sw = new Stopwatch();
    sw.Start();

    //耗时巨大的代码

    sw.Stop();
    TimeSpan ts2 = sw.Elapsed;
    Console.WriteLine("Stopwatch总共花费{0}ms.", ts2.TotalMilliseconds);
}

第三种用API实现：

[System.Runtime.InteropServices.DllImport("Kernel32.dll")]
static extern bool QueryPerformanceCounter(ref long count);
[System.Runtime.InteropServices.DllImport("Kernel32.dll")]
static extern bool QueryPerformanceFrequency(ref long count);
static void SubTest()
{
    long count = 0;
    long count1 = 0;
    long freq = 0;
    double result = 0;
    QueryPerformanceFrequency(ref freq);
    QueryPerformanceCounter(ref count);

    //耗时巨大的代码

    QueryPerformanceCounter(ref count1);
    count = count1 - count;
    result = (double)(count) / (double)freq;
    Console.WriteLine("QueryPerformanceCounter耗时: {0} 秒", result);
}