12.10. Chapter Summary
In this chapter, we started with a misbehaving system and used performance tools to pinpoint which subsystem was used excessively (the disk subsystem as shown by vmstat) and which component caused the problem (prelink). We then investigated the prelink application to determine why it used so much disk I/O (using strace). We discovered in prelink's documentation a cached mode that should dramatically reduce disk I/O. We investigated the performance of the cached mode and found that it did not eliminate disk I/O as much as it should, because it was trying to prelink files that could not be prelinked. We then simulated a cache that avoided trying to prelink files that could not be prelinked and verified that it significantly reduced the amount of disk I/O and runtime of prelink in quick mode. Finally, we submitted a bug report to the author of prelink in the hopes that the author will recognize the problem and fix it. This chapter was the last chapter of Linux performance hunts.
In the next chapter, the final chapter, we look at the higher-level picture of Linux performance and performance tools. We review methodologies and tools covered in this book and look at some of the areas of Linux performance tools that are ripe for improvement.