Hello, that's an interesting question!
I'm currently reading the same book, but you've read more than me so far :)

On Mon, Aug 01, 2016 at 08:36:07AM +0300, Aleksander Alekseev wrote:

* bogomips value (see `cat /proc/cpuinfo`) is determined only once
  during system boot

As far as I know, I is (was?) the case.

It's my understanding that it shouldn't work. CPU frequency actually
changes manually (see cpufrequtils) and/or automatically depending for
instance on laptop's current battery charge. There is also such a nasty
thing as Intel Turbo Boost. In other words actual MIPS could be higher
or lower than measured MIPS. So udealy() can't guarantee anything.

Makes sense. Do you have such machine? Did you try to get bogomips and then
reduce your CPU count / speed and get that number again?

Maybe this value is now dynamic.

Also, did you actually try udealay() in high/low frequency to see wether you
see an actual difference between runs?

Sorry I don't have final answers!

-- 
Fran?ois