addind to Ivans stmt:
.... and it could be anywhere between 0 (at the right
spot executed in parallel to previous/next) and 50 or more micro-cycles
(ie. after an SPKA).
The hardware now has (since z10) extra instructions to get the number
of instructions executed and the number of stalls and the number of
cycles per instruction for a given time slot and a lot of other usefull
information. It is called measurement and counter facility and has
(aside of the various model-specifc as well as common counters)
instructions to sample the cpu 1.000.000 million times per second. so
can get a picture of where the code spends most of the time.
It is an extra book next to POP