The Pendulum Swinging Back and Forward With Architecture

In the book, you explain how the hardware and the compiler can subvert your attempts to measure how long individual instructions take. So if i wrote a four loop to do an operation ten thousand times and time that loop, what are some less obvious ways might make my timings inaccurate? I gan to give a little context first. People talk about the pendulum swinging back and forth with architecture,. both hard war and software. In the book, part of the purpose is to get a bunch of grad students, whoave come from different backgrounds, all on the same page.