Program profiling

Some help from skilled professionals is badly needed :-(
I've got a ILE/C program (wrote myself), that makes some pretty complicated 
data base processing. And it is somehow too-oo-ooooo slow. I suspected some 
pieces of code, applied some optimization to it, but without real effect. 

It is still slow.

What I'd like to do is to make some profiling - for example at function call 
level. It would at least allow me to concentrate on the bottleneck and not to 
spend time on unimportant code.

Never did that in this environment. Can someone direct me to a simple guide on 
how to apply and analyze profiling data?

TIA,

Jevgeni Astanovski
Sampo Bank,
Tallinn, Estonia.