Nobody writing high-performance code for these machines has that documentation. They largely do ok anyway because the time of cycle counting is long in the past

Nobody writing high-performance code for these machines has that documentation. They largely do ok anyway because the time of cycle counting is long in the past and the name of the game involves cache effects and synchronization that is very hard to reason about individually but clearly visible if taken in aggregate. You don't get a cookie if you can accurately time 10 instructions, but you do if your matrix multiply over a hundred million of them is 1% faster.