Wringing the value out of every processor cycle on your machine required a variety of approaches. Sure, your code has to be efficient, but you also have to have your disks configured correctly, and a multitude of other things. Swayam Prakash provides a guide to some of the lower hanging fruit you can pick.
From the article:
Performance optimization in Linux doesn't always mean what we might think. It's not just a matter of outright speed; sometimes it's about tuning the system so that it fits into a small memory footprint. You'd be hard-pressed to find a programmer that does not want to make programs run faster, regardless of the platform. Linux programmers are no exception; some take an almost fanatical approach to the job of optimizing their code for performance. As hardware becomes faster, cheaper, and more plentiful, some argue that performance optimization is less critical--particularly people that try to enforce deadlines on software development.
Note this this article is all about application optimization and not about server level optimization.