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POCan't get even a simple method to inline (?)
 

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  1. POCan't get even a simple method to inline (?)
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    <p>Logically, I always assumed that very short and simple methods would get inlined by the C# Compiler and thus won't show any overhead compared to simply typing the code in the methods by hand...</p> <p>Until today - when I tried to benchmark various methods and manually inlined code. Turns out that (for me) even the most simple code will show a method call overhead compared to its manually inlined counterpart.<br/> Actually, I could find no clues as to <em>any</em> method being inlined - So I ran a simple test.</p> <p>System used:</p> <ul> <li>Intel C2D E7200 (Dual Core) 2.53GHz</li> <li>4GB DDR2</li> <li>Windows 7 64bit</li> <li>.NET 4.0</li> <li>Visual Studio 2010 Ultimate</li> </ul> <p>All tests were performed <strong>without Debug</strong> and using <strong>Release Configuration (Optimize Code)</strong>.</p> <p>Here's the code I used to benchmark:</p> <pre><code>static void Main() { const int iterations = 250000000; // 250 million iterations Thread.Sleep(1000); // sleep for one second var sw = new Stopwatch(); int s = 0; sw.Start(); for (int i = 0; i &lt; iterations; i++) { // incrementing s by 1 in various ways } sw.Stop(); Console.WriteLine("Time: {0}ms", sw.ElapsedMilliseconds); } </code></pre> <p><strong>[1]</strong> First, I've simply benchmarked a simple increment command:</p> <pre><code>// in Main for (int i = 0; i &lt; iterations; i++) { s = s + 1; } </code></pre> <p>Results from 5 runs:</p> <ol> <li>867ms</li> <li>877ms</li> <li>868ms</li> <li>865ms</li> <li>870ms</li> </ol> <hr> <p><strong>[2]</strong> Switching to a method call:</p> <pre><code>static int Increment(int a) { return a + 1; } </code></pre> <p>...</p> <pre><code>// in Main for (int i = 0; i &lt; iterations; i++) { s = Increment(s); } </code></pre> <p>Results from 5 runs:</p> <ol> <li>2161ms</li> <li>2159ms</li> <li>2194ms</li> <li>2177ms</li> <li>2163ms</li> </ol> <p>Ouch! Obviously there's an overhead for the method. </p> <p>I've tried to use reflection, and printed <code>MethodBase.GetCurrentMethod().Name</code> from within the <code>Increment</code> method; it was indeed printing <code>Increment</code> - meaning the method isn't inlined.</p> <p>Next I've tried to add the <code>[MethodImpl(MethodImplOptions.NoInlining)]</code> attribute to the method - <strong>but the benchmark time stayed exactly the same</strong>.</p> <p>In Debug mode and with Optimize Code set to false, the first test is slightly slower while the second one is about two times slower; and yet again the <em>NoInlining</em> attribute doesn't impact performance.</p> <hr> <p><strong>Am I doing something wrong here that I fail to make even such a simple method work without an overhead? Why is this happening?</strong><br/> Surely this can't be expected behavior - or is it?</p> <p><em>Note: Similar testing in Java shows no overhead to such a method call. (using Eclipse + JDK 1.7, Java also seems to be <strong>A LOT</strong> faster at this.)</em></p>
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    1. COnote that in .NET 4.5 you can actually force the compiler to try and inline your method: http://msdn.microsoft.com/en-us/library/system.runtime.compilerservices.methodimploptions%28v=VS.110%29.aspx
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