如何计算一段程序逻辑运行时间？

--

class Program
    {

        [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);
        [STAThread]
        static void Main(string[] args)
        {
            Console.WriteLine("开始执行操作
");
            long count = 0;
            long count1 = 0;
            long freq = 0;
            double result = 0;

            QueryPerformanceFrequency(ref freq);
            QueryPerformanceCounter(ref count);

            #region 程序逻辑执行部分
            int times = 20;
            int value = 1;
            string filePath = "D://123.txt";

            do
            {
                if (!File.Exists(filePath))
                {
                    var file = File.Create(filePath);
                    file.Close();
                    File.WriteAllText(filePath, "1");
                }
                else
                {
                    value = Convert.ToInt32(File.ReadAllText(filePath));
                    value++;
                    File.WriteAllText(filePath, value.ToString());
                    times--;
                }
                Console.WriteLine(value);
            } while (times > 0); 
            #endregion

            QueryPerformanceCounter(ref count1);
            count = count1 - count;
            result = (double)(count) / (double)freq;
            Console.WriteLine("结束操作，当前程序耗时: {0} 秒", result);
            Console.ReadLine();
        }