Just playing with clocks

Program.cs

using System;
using System.Runtime.InteropServices;

namespace PreciseTimeTest
{
    public class Program
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("------------------------------------");
            Console.WriteLine("DateTime.UtcNow");
            Console.WriteLine("------------------------------------");

            for (int i = 0; i < 10; i++)
            {
                Console.WriteLine(DateTime.UtcNow.ToString("o"));
            }

            Console.WriteLine();

            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            {
                Console.WriteLine("------------------------------------");
                Console.WriteLine("GetSystemTimeAsFileTime");
                Console.WriteLine("------------------------------------");

                for (int i = 0; i < 10; i++)
                {
                    Console.WriteLine(GetNowWindows().ToString("o"));
                }

                Console.WriteLine();

                Console.WriteLine("------------------------------------");
                Console.WriteLine("GetSystemTimePreciseAsFileTime");
                Console.WriteLine("------------------------------------");

                for (int i = 0; i < 10; i++)
                {
                    Console.WriteLine(GetPreciseNowWindows().ToString("o"));
                }

                Console.WriteLine();
            }
            else
            {
                Console.WriteLine("------------------------------------");
                Console.WriteLine("clock_gettime(CLOCK_REALTIME_COARSE)");
                Console.WriteLine("------------------------------------");

                for (int i = 0; i < 10; i++)
                {
                    Console.WriteLine(GetTimeLinuxTime(CLOCK_REALTIME_COARSE).ToString("o"));
                }

                Console.WriteLine();

                Console.WriteLine("------------------------------------");
                Console.WriteLine("clock_gettime(CLOCK_REALTIME)");
                Console.WriteLine("------------------------------------");

                for (int i = 0; i < 10; i++)
                {
                    Console.WriteLine(GetTimeLinuxTime(CLOCK_REALTIME).ToString("o"));
                }

                Console.WriteLine();
            }
        }

        private const int CLOCK_REALTIME = 0;
        private const int CLOCK_REALTIME_COARSE = 5;
        
        private static DateTime GetTimeLinuxTime(int clockId)
        {
            timespec ts;
            clock_gettime(clockId, out ts);
            var dto = DateTimeOffset.FromUnixTimeSeconds(ts.tv_sec).AddTicks(ts.tv_nsec / 100);
            return dto.UtcDateTime;
        }

        private static DateTime GetPreciseNowWindows()
        {
            long timeStamp;
            GetSystemTimePreciseAsFileTime(out timeStamp);
            return DateTime.FromFileTimeUtc(timeStamp);
        }

        private static DateTime GetNowWindows()
        {
            long timeStamp;
            GetSystemTimeAsFileTime(out timeStamp);
            return DateTime.FromFileTimeUtc(timeStamp);
        }

        [DllImport("kernel32.dll")]
        static extern void GetSystemTimeAsFileTime(out long timeStamp);

        [DllImport("kernel32.dll")]
        static extern void GetSystemTimePreciseAsFileTime(out long timeStamp);

        [DllImport("libc")]
        static extern void clock_gettime(int clk_id, out timespec ts);

        [StructLayout(LayoutKind.Sequential)]
        struct timespec
        {
            public long tv_sec;
            public long tv_nsec;
        }
    }
}

results-Linux.txt

------------------------------------
DateTime.UtcNow
------------------------------------
2017-01-30T22:56:30.9340520Z
2017-01-30T22:56:31.5351510Z
2017-01-30T22:56:31.5351510Z
2017-01-30T22:56:31.5355800Z
2017-01-30T22:56:31.5355800Z
2017-01-30T22:56:31.5355800Z
2017-01-30T22:56:31.5355800Z
2017-01-30T22:56:31.5355800Z
2017-01-30T22:56:31.5355800Z
2017-01-30T22:56:31.5360790Z

------------------------------------
clock_gettime(CLOCK_REALTIME_COARSE)
------------------------------------
2017-01-30T22:56:31.5390800Z
2017-01-30T22:56:31.5390800Z
2017-01-30T22:56:31.5390800Z
2017-01-30T22:56:31.5390800Z
2017-01-30T22:56:31.5390800Z
2017-01-30T22:56:31.5395800Z
2017-01-30T22:56:31.5395800Z
2017-01-30T22:56:31.5395800Z
2017-01-30T22:56:31.5395800Z
2017-01-30T22:56:31.5395800Z

------------------------------------
clock_gettime(CLOCK_REALTIME)
------------------------------------
2017-01-30T22:56:31.5402917Z
2017-01-30T22:56:31.5403714Z
2017-01-30T22:56:31.5404506Z
2017-01-30T22:56:31.5405293Z
2017-01-30T22:56:31.5406270Z
2017-01-30T22:56:31.5407252Z
2017-01-30T22:56:31.5408059Z
2017-01-30T22:56:31.5408890Z
2017-01-30T22:56:31.5409740Z
2017-01-30T22:56:31.5410542Z

results-Windows.txt

------------------------------------
DateTime.UtcNow
------------------------------------
2017-01-30T22:57:10.0354444Z
2017-01-30T22:57:10.0359440Z
2017-01-30T22:57:10.0359440Z
2017-01-30T22:57:10.0359440Z
2017-01-30T22:57:10.0359440Z
2017-01-30T22:57:10.0359440Z
2017-01-30T22:57:10.0359440Z
2017-01-30T22:57:10.0359440Z
2017-01-30T22:57:10.0359440Z
2017-01-30T22:57:10.0359440Z

------------------------------------
GetSystemTimeAsFileTime
------------------------------------
2017-01-30T22:57:10.0369431Z
2017-01-30T22:57:10.0369431Z
2017-01-30T22:57:10.0369431Z
2017-01-30T22:57:10.0369431Z
2017-01-30T22:57:10.0369431Z
2017-01-30T22:57:10.0369431Z
2017-01-30T22:57:10.0369431Z
2017-01-30T22:57:10.0369431Z
2017-01-30T22:57:10.0369431Z
2017-01-30T22:57:10.0374442Z

------------------------------------
GetSystemTimePreciseAsFileTime
------------------------------------
2017-01-30T22:57:10.0378719Z
2017-01-30T22:57:10.0379613Z
2017-01-30T22:57:10.0380116Z
2017-01-30T22:57:10.0389834Z
2017-01-30T22:57:10.0397068Z
2017-01-30T22:57:10.0404611Z
2017-01-30T22:57:10.0411557Z
2017-01-30T22:57:10.0418727Z
2017-01-30T22:57:10.0426010Z
2017-01-30T22:57:10.0433040Z

Notice the spacing between values. Only GetSystemTimePreciseAsFileTime and clock_gettime(CLOCK_REALTIME) show reasonable separation of values.