How to trace and profile all low level calls (c libraries) being used by a mod_perl or a mod_php application?

Question

I've seen once on a site, a call graph digging into the most low level libraries of a web request initiated by a PHP appplication with call timings and summary. Seems to me that this is a great way to spot the reason of bottlenecks that aren't obvious while profiling PHP-only code.

Something like strace does but with far more detail.

Answer 1

Rasmus mentioned valgrind a couple times in his presentations. If I remember correctly it measures IO, memory, etc. Might want to take a look.

Answer 2

Tools like VTune helps here. You can point this tool at a process or a system to profile and it will help find performance hotspots. VTune also has a call graph mode.