Brion Vibber <vibber(a)aludra.usc.edu> posted some nice stats, showing that the CPU usage is primarily in the Apache daemons. So, a profiler/hotspot/gprof-like tool for PHP would be useful. I found "APD" (as well as APC, a PHP compilation caching tool) at: http://www.omniti.com/~george/php/ I didn't find any other PHP profiling tools, though perhaps they're out there. Of course, an alternative could be to run gprof itself against the Apache daemon (including PHP). Perhaps there's a hotspot in the underlying Apache/PHP implementation; fixing that would help Wikipedia and probably many others too. Anybody have a test platform willing to run the profile? Again, I don't have such a setup :-(.