10.2. Identify a Problem

The first step in a performance hunt it to identify a problem to investigate. In this case, I chose to investigate a performance problem that crops up when using GIMP, an open-source image-manipulation program. GIMP can slice and dice various aspects of an image, but it also has a powerful set of filters that can warp and change an image in a variety of ways. These filters can change the appearance of the image based on some complicated algorithms. Typically, the filters take a long time to complete and are very CPU-intensive. One of the filters in particular, Van Gogh (LIC), takes an input image and modifies it so that it looks like a painting done in the style of Van Gogh. This filter takes a particularly long amount of time to complete. When running, the filter uses nearly 100 percent of CPU and takes several minutes to complete. The amount of time to complete depends on the size of the image, the machine's CPU speed, and the values of the parameters passed into the filter. In this chapter, we investigate why this filter is so slow using Linux performance tools and see whether there is any way to speed it up.