Can sysprof generate in-kernel callgraphs?

Hi,

Is it possible to get in-kernel callgraphs when profiling with
sysprof, and if so how can it be used?
I've installed debug packages for my kernel, however I still only get
"in kernel: xy%" displayed, without any further information where the
time has been spent inside the kernel.

Thank you in advance, Clemens Eisserer