Profiler for multithreaded applications

[michiguel]

What do you use? (preferably for Linux and free). I heard gprof is not good.

How about this?
http://oprofile.sourceforge.net/news/

Miguel

[Rémi Coulom]

I also use sysprof. sysprof has the advantage of a GUI, immediately usable without reading any documentation. Using oprofile is a bit complicated, but maybe more powerful.
http://www.daimi.au.dk/~sandmann/sysprof/

Rémi

[Gian-Carlo Pascutto]

The performance monitoring tools in the kernel itself. (It's just called "perf").

KCachegrind + callgrind.