Blender 3.2 100% CPU Spikes During Cycles GPU Render

Hi All,

I’ve run into a confusing issue(?) in Blender 3.2 and I’d love some help either resolving it, or understanding why it is happening.

My setup:
Win 10
Intel i9-10850

Scene info:
24fps animation (quite long, if that matters, ~8500 frames)
1920 x 1080, High Quality H.264 MPEG4 output
The scene is quite large though, it uses output from BlenderGIS, a .tif that is ~750 MB.
Otherwise it is a quite simple animation, some lighting and a camera.

In Blender 3.2, during GPU render in Cycles, all cores on my CPU spike to 100% during frame renders. See below.

However, my GPU is clearly doing some of the work though.
(New users can’t post more than one image, but task manager shows Copy and CUDA processes for GPU jumping from 0 to ~75% utilization for every frame render).

To compare, I opened the same scene in Blender 2.93 and the results are more what you’d expect, GPU usage is close to 100%, CPU is mostly idle.

An interesting difference between 3.2 and 2.93 is that each frame takes 1/3 the time to render in 3.2, compared to 2.93.

  • Can this high CPU usage be explained?
  • Is this the CPU transferring scene data back and forth from the GPU?
  • Why is my “Dedicated GPU memory usage” maxed out in the GPU?
    • As an experiment, I deleted most of the scene…GPU memory usage was no longer maxed, CPU usage still spiked.
  • Can this be alleviated?

I’d be happy to provide more details if needed.