On the Affinity Bridge blog today there's a great post looking at the use of Xdebug and KCachegrind to pinpoint bottlenecks and possible refectoring points in your code in a bit more visual way. They use an example from their own development - a script that took around twenty minutes to run.

By reducing the number of queries, making small code optimizations, and properly indexing and keying the legacy database we managed to cut the time to 10 minutes—still we were way off target. To get a better look at what was going on, we thought it would be great to install Xdebug and take a look at it with KCacheGrind.

They show you how to get the full setup installed (on a Ubuntu system) - the LAMP stack, Xdebug and KCacheGrind. Complete commands to install, configure and run a sample debug session are all included. Sample outputs from the KCacheGrind software are there too: code structure, execution times.