Shawn Hargreaves Blog
When C# code runs too slowly, you can profile it to see where the time is being spent.
Graphics programmers are not so lucky. If you work for a big commercial studio and have access to an Xbox devkit, the Xbox version of PIX gives nearly as much information about GPU performance as profilers can tell you about the CPU, but for the rest of us the GPU remains a mysterious black box which cannot be so easily measured.
I like to think of GPU performance investigation as a Sherlock Holmes mystery:
We must gather clues, form a hypothesis, and then confront the villain to make them confess.
We do have one advantage over the original Mr. Holmes, and that is the ability to rewind time and run our program again with minor changes. This is an incredibly powerful tool. Let's say the evidence leads us to suspect Performance was killed by Colonel Mustard, in the library, with the candlestick. To confirm this theory, we can comment out our candlestick rendering code, and run the program again. Is Performance still dead? If she lives, we know the murder weapon was the candlestick, so should probably investigate how many polygons that is built from, and how expensive a shader it is using.
To be successful with this kind of investigation, two things are required:
You have an intelligently entertaining style of writing. I enjoy your posts, and look forward to a continuation of this one especially.