I’m experiencing a strange behavior on my workstation:
Hardware and software configuration:
CPU: AMD Threadripper 3990X (128 cores)
RAM: 256 GB
OS: Windows 11 (latest update installed – September 2025, KB5065426, build 26100.6584)
Corona version: 13 Hotfix 1
When checking the Windows Task Manager, I noticed that the 128 cores of the processor are not fully utilized during rendering (both interactive and final). CPU usage generally stays between 80–90%, with only occasional peaks above 90%, but it never reaches a constant 100%.
I have tested this on many different scenes, both heavy and light, and the behavior is always the same. My system works perfectly otherwise, and I have no hardware or performance issues outside rendering. For this reason, I don’t think it’s useful to send you a test scene, since the issue happens consistently with every render.
As far as I remember, Corona used to fully load the CPU at 100% in the past. I know that performance drops can sometimes occur with CPUs that have a very high core count, but I thought this had been resolved since Corona 12.
Could you please confirm whether you observe the same kind of limitation when testing Corona on a Threadripper 3990X (or an equivalent 128-core CPU) in your labs?
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.
Same here with AMD 5950x. Both IR and rendering utilize no more than 80 percent and percentage drops throughout the render process. Latest windows 11 updates installed. Same thing occurred with Corona 13 hot fix 1, now carries over hotfix 2. Overall Corona has become. slower than Corona 11.
Same things happens with an empty scene as well. Corona 13 hotfix 2 , 3ds max 2024 latest packs, latest win 11 updates.
Hello, thank you very much for your feedback. I also did a test last week with Vray and it’s exactly the same, none of the logical processors reach 100% (more like between 80 and 90%). I imagine that the Windows task manager has been modified and that it is perhaps more “refined” than before… For my part, I don’t particularly feel any slowdown of corona from version to version but I was wondering about this display of the task manager which previously showed a processor usage at 100% during renderings (I’m sure that was the case.)
Ha i expierienced the same … just under another topic.
Have a threadripper 9980X with 64cores /128threads but when rendering with corona or scanline in 3dsmax i have various cpu-usage between 82 and 97% … but in average around 90%.
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