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copied!<p>Your issue is your test. When you are benchmarking code there are a couple of guiding principals you should always follow:</p> <ol> <li>Processor Affinity: Use only a single processor, usually not #1.</li> <li>Warmup: Always perform the test a small number of times up front.</li> <li>Duration: Make sure your test duration is at least 500ms.</li> <li>Average: Average together multiple runs to remove anomalies.</li> <li>Cleanup: Force the GC to collect allocated objects between tests.</li> <li>Cooldown: Allow the process to sleep for a short-period of time.</li> </ol> <p>So using these guidelines and rewriting your tests I get the following results:</p> <p><strong>Run 1</strong></p> <pre> Enter test number (1|2): 1 ListSum averages 776 ListSum averages 753 ArraySum averages 1102 ListSum averages 753 Press any key to continue . . . </pre> <p><strong>Run 2</strong></p> <pre> Enter test number (1|2): 2 ArraySum averages 1155 ArraySum averages 1102 ListSum averages 753 ArraySum averages 1067 Press any key to continue . . . </pre> <p>So here is the final test code used:</p> <pre><code>static void Main(string[] args) { //We just need a single-thread for this test. Process.GetCurrentProcess().ProcessorAffinity = new IntPtr(2); System.Threading.Thread.BeginThreadAffinity(); Console.Write("Enter test number (1|2): "); string input = Console.ReadLine(); //perform the action just a few times to jit the code. ListArrayLoop warmup = new ListArrayLoop(10, 10); Console.WriteLine("Performing warmup..."); Test(warmup.ListSum); Test(warmup.ArraySum); Console.WriteLine("Warmup complete..."); Console.WriteLine(); ListArrayLoop test = new ListArrayLoop(10000, 10000); if (input == "1") { Test(test.ListSum); Test(test.ListSum); Test(test.ArraySum); Test(test.ListSum); } else { Test(test.ArraySum); Test(test.ArraySum); Test(test.ListSum); Test(test.ArraySum); } } private static void Test(Action test) { long totalElapsed = 0; for (int counter = 10; counter > 0; counter--) { try { var sw = Stopwatch.StartNew(); test(); totalElapsed += sw.ElapsedMilliseconds; } finally { } GC.Collect(0, GCCollectionMode.Forced); GC.WaitForPendingFinalizers(); //cooldown for (int i = 0; i < 100; i++) System.Threading.Thread.Sleep(0); } Console.WriteLine("{0} averages {1}", test.Method.Name, totalElapsed / 10); } </code></pre> <p><em>Note:</em> Some people may debate about the usefulness of the cool-down; However, everyone agrees that even if it's not helpful, it is not harmful. I find that on <em>some</em> tests it can yield a more reliable result; however, in the example above I doubt it makes any difference.</p>

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