Firing timers

[Nicola Manica]

Hi, I'm a student that want to study the kernel code.
I have a simple question:
If I set an hrtimer, I think that when it expires it raise a timer
interrupt. What is the sequence of functions called at this point (in a
recent kernel for example 2.6.29)?
How I can know which is the timer expired?
Thanks for the reply, and maybe sorry for the stupid question.
Nicola