Kernel & User space timers: somebody has got links?

I was going through kernel/timers.c & kernel/hrtimers.c and realized that there are lots and lots of timers present in kernel for kernels and userspace code.. Like posix timers, itimers, clockevents, etc..

Does somebody have a link to documentation or slides that list all these and what they are for? That would be very helpful to understand all the timer usecases we have in kernel..

-- viresh