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POHow do I learn enough about CLR to make educated guesses about performance problems?
 

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  1. POHow do I learn enough about CLR to make educated guesses about performance problems?
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    <p>Yes, I <em>am</em> using a profiler (ANTS). But at the micro-level it cannot tell you how to fix your problem. And I'm at a microoptimization stage right now. For example, I was profiling this:</p> <pre><code>for (int x = 0; x &lt; Width; x++) { for (int y = 0; y &lt; Height; y++) { packedCells.Add(Data[x, y].HasCar); packedCells.Add(Data[x, y].RoadState); packedCells.Add(Data[x, y].Population); } } </code></pre> <p>ANTS showed that the y-loop-line was taking a lot of time. I thought it was because it has to constantly call the Height getter. So I created a local <code>int height = Height;</code> before the loops, and made the inner loop check for <code>y &lt; height</code>. That actually made the performance worse! ANTS now told me the x-loop-line was a problem. Huh? That's supposed to be insignificant, it's the outer loop!</p> <p>Eventually I had a revelation - maybe using a property for the outer-loop-bound and a local for the inner-loop-bound made CLR jump often between a "locals" cache and a "this-pointer" cache (I'm used to thinking in terms of CPU cache). So I made a local for Width as well, and that fixed it.</p> <p>From there, it was clear that I should make a local for Data as well - even though Data was not even a <em>property</em> (it was a field). And indeed that bought me some more performance.</p> <p>Bafflingly, though, reordering the x and y loops (to improve cache usage) made zero difference, even though the array is huge (3000x3000).</p> <p>Now, I want to learn <em>why</em> the stuff I did improved the performance. <strong>What book do you suggest I read?</strong></p>
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    1. USStefan Monov
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      1. POHow do I learn enough about CLR to make educated guesses about performance problems?
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    1. COThis is a very interesting subject. Another interesting question is how do you make performance-related design decisions? For example, "How can I tell when to use a `struct` and give up subclassing in exchange for better performance?"
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      1. POHow do I learn enough about CLR to make educated guesses about performance problems?
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    2. COHave you measured and confirmed the performance improvements on release code with no debugger or profiler attached?
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      1. POHow do I learn enough about CLR to make educated guesses about performance problems?
      1. USAlbin Sunnanbo
    3. COAlbin - no. Honestly I didn't think that running outside a profiler would change the performance difference, so I didn't bother. You think I should have? Has that been a problem for you before? (I *am* compiling with optimizations on though)
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