Oprofile

From oprofile.sourceforge.net

apt-get install oprofile oprofile-gui prospect

Then you can read file:///usr/share/doc/oprofile/oprofile.html
If you want to profile also the kernel you need the uncompressed version of the kernel.
Unfortunately under Debian this is not possible just like that, what you can do is recompiling the kernel with "make vmlinux", cf this post