Question

Yes, I am 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:

for (int x = 0; x < Width; x++)
{
    for (int y = 0; y < Height; y++)
    {
        packedCells.Add(Data[x, y].HasCar);
        packedCells.Add(Data[x, y].RoadState);
        packedCells.Add(Data[x, y].Population);
    }
}

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 int height = Height; before the loops, and made the inner loop check for y < height. 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!

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.

From there, it was clear that I should make a local for Data as well – even though Data was not even a property (it was a field). And indeed that bought me some more performance.

Bafflingly, though, reordering the x and y loops (to improve cache usage) made zero difference, even though the array is huge (3000×3000).

Now, I want to learn why the stuff I did improved the performance. What book do you suggest I read?

Answer 1

CLR via C# by Jeffrey Richter.

It is such a great book that someone stolen it in my library together with C# in depth.