Interface generic methods call time microbenchmark

GenericBenchmark.cs

using System;
using System.Diagnostics;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;

namespace GenericBencmark
{
    class Program
    {

        public interface ITest
        {
            void Generic<T>(T arg);

            void NonGeneric(long arg);
        }

        public class Test : ITest
        {
            public bool isEnabled = false;
            public bool IsEnabled { get { return isEnabled; } }

            public void Generic<T>(T arg)
            {
                if (IsEnabled)
                    DoLog(arg);
            }

            public void NonGeneric(long arg)
            {
                if (IsEnabled)
                    DoLog(arg);
            }

            [MethodImpl(MethodImplOptions.NoInlining)]
            private void DoLog<T>(T arg) { }

        }

        [MethodImpl(MethodImplOptions.NoInlining)]
        private static void Spin<T>(T arg) { }


        public static void Main()
        {
            int iterations = 1000 * 1000 * 1000;
            long value = new Random().Next();
            Test testInst = new Test() { isEnabled = false };
            ITest testItf = testInst;

            testItf.Generic(value);
            testItf.NonGeneric(value);

            var swLoop = Stopwatch.StartNew();
            for (int i = 0; i < iterations; i++)
            {
                Spin(value);
            }
            swLoop.Stop();

            var swNonGeneric = Stopwatch.StartNew();
            for (int i = 0; i < iterations; i++)
            {
                Spin(value);
                testItf.NonGeneric(value);
            }
            swNonGeneric.Stop();
            var swGeneric = Stopwatch.StartNew();
            for (int i = 0; i < iterations; i++)
            {
                Spin(value);
                testItf.Generic(value);
            }
            swGeneric.Stop();


            var swInstNonGeneric = Stopwatch.StartNew();
            for (int i = 0; i < iterations; i++)
            {
                Spin(value);
                testInst.NonGeneric(value);
            }
            swInstNonGeneric.Stop();
            var swInstGeneric = Stopwatch.StartNew();
            for (int i = 0; i < iterations; i++)
            {
                Spin(value);
                testInst.Generic(value);
            }
            swInstGeneric.Stop();

            Console.WriteLine(swLoop.Elapsed);
            Console.WriteLine("Instance Generic: {0:0.00} ns/call", ConvertToNsPerIteration(swInstGeneric.Elapsed - swLoop.Elapsed, iterations));
            Console.WriteLine("Instance NonGeneric: {0:0.00} ns/call", ConvertToNsPerIteration(swInstNonGeneric.Elapsed - swLoop.Elapsed, iterations));
            Console.WriteLine("Interface Generic: {0:0.00} ns/call", ConvertToNsPerIteration(swGeneric.Elapsed - swLoop.Elapsed, iterations));
            Console.WriteLine("Interface NonGeneric: {0:0.00} ns/call", ConvertToNsPerIteration(swNonGeneric.Elapsed - swLoop.Elapsed, iterations));
            

        }

        private static double ConvertToNsPerIteration(TimeSpan elapsed, int iterations)
        {
            return elapsed.TotalSeconds*1000000000/iterations;
        }
    }
}