A couple of months ago, when I first tried rendering with optix I was blown away by the difference in speed. On my current project scene I had a x4 speed up in render times compared to CUDA.
I use a i9, 2080ti at work.
Recently I heard that 2.92 allowed to use both CPU and GPU with Optix, so I gave it a try, thinking that my i9 was going to be of some use.
However, I noticed that there was a significant slow down when checking CPU as well as GPU in the optix panel. Not by much, but the few tests I did were consistant.
I setup a quick test scene, a Nishita sky for the environment, a plane emitting 2500 icospheres as hair, and 100 interpolated children, with a standard principled shader. So only geometry, no animation.
Here are my results :
2.91 + Optix (GPU), TS 64 = 16.34, 15.48, 15.17
2.92 + Optix (GPU+CPU) TS 64 = 18.14, 18.38, 18.18
2.92 + Optix (GPU) TS 64 = 15.55, 15.69
2.91 + Optix (GPU), TS 256 = 11.62, 11.74
2.92 + Optix (GPU+CPU) TS 256 = 13.64, 13.97
2.92 + Optix (GPU) TS 256 = 11.92, 11.95
Is there a reason for this ? Certain circumstances for which the CPU is beneficial, others when it is not ? I realise that my test scene is very limited, no skinning, no motion blur, but it is a fairly good representation of the current project I am working on, for which I am trying to optimize render times)