3 ms·

Thanks for the very concise explanation. It seems obvious now that you’ve put it into those terms.

• dragontamer 5y ago
  The main "difficulty" is that "Rdtsc" has itself a large execution time, and that modern processors have a very strange definition of "execute". With retirement queue sizes ranging from 300 to 600 (depending on architecture), your singular CPU-core could very well be "executing" 600+ instructions simultaneously, including "rdtsc". Under such conditions, the "definition" of "get the current time" is quite ambiguous. ----------- This isn't a problem with bandwidth. But it makes measuring "latency" very difficult, especially because out-of-order execution means that "proper" latency is largely ignored. ------- Because of the out-of-order execution models of modern processors, "reciprocal bandwidth", or "instructions-per-clock" tends to be more important than latency proper.