I’m not a hardware expert so it would be best to wait for one of our Gurus, but I think non-100% CPU usage is normal and caused by the way Windows is reporting it and the quirks of CPUs with high core count. I made an experiment in a simple scene using one of our office 3990X:
- rendered “as is” - the CPU usage reported by the Windows Task Manager was around 70-80% (so even lower than for you
) - installed Ryzen Master, enabled manual overclocking, set all core speed to 3100 (it never reached such a high value while rendering anyway), and memory clock to 1600MHz (x2 = 3200, with the same speed for memory and infinity fabric, so “coupled mode”) - in this case the CPU usage was higher (over 90%)
I also noticed that the CPU usage is scene-dependent. For example, if you render a small object against a solid background the CPU usage will be lower than in the case of rendering lots of objects covering the whole view.
And there is also this:
Even if the application was able to keep all the execution units fully utilized, it may not be able to feed them with data fast enough. Modern CPUs are a few orders of magnitude faster than modern RAM, so when the CPU is able to process the data faster than the memory is able to supply it, the CPU will end up waiting for the data most of the time.