Looks like you have found one answer by providing a function name to s (step).
Another way is to c <sub name> or b <sub name>
Yet another method, is to edit the source to force a breakpoint. If you add DB::single = 1; to your code then the debugger will stop on the next statement.
This can be very helpful if the fully qualified name of your function is not clear, or if it is dynamically compiled. It can be a problem though as once you set a breakpoint that way, you can't turn it off without editing your code again and restarting your program.