RTX vs CUDA Engine Type Issue (bug?)

[Streetwise]

I have a scene that hangs up on "Building GPU Light Cache" (both IPR and Render), but if I switch the Engine Type to CUDA and uncheck the CPU box, there are no issues. Why would this be the case? Also, I was under the impression that the difference between RTX/CUDA was that CUDA offers a hybrid approach for both CPU and GPU, whereas RTX is GPU only. A friend says that RTX renders much faster than CUDA, even with the CPU box unchecked. Thoughts?

[Muhammed_Hamed]

Hi Streetwise , thanks for the report

I have a scene that hangs up on "Building GPU Light Cache" (both IPR and Render), but if I switch the Engine Type to CUDA and uncheck the CPU box, there are no issues. Why would this be the case?

Could you please share a simple version of the scene here? I will make sure this hang is solved
What V-Ray Build and what driver?

Also, I was under the impression that the difference between RTX/CUDA was that CUDA offers a hybrid approach for both CPU and GPU, whereas RTX is GPU only. A friend says that RTX renders much faster than CUDA, even with the CPU box unchecked. Thoughts?

RTX and CUDA modes share most of the code, you are fine using either.
Some scenes will render faster with RTX mode, if you have a lot of grass or hair for example this speed boost can be significant. Other than that, Cuda is very close/similar in performance

Best,
Muhammed

[Streetwise]

Muhammed_Hamed Could I DM you with a link to the scene? A simplified version seems to work okay. It's when there are all of the assets that it hangs up. So it's a fairly large scene.

The team member that is having the issue is on V-Ray 5 Update 2.3 and a driver of 471.68. I'm personally on 512.15 and Update 2.3 and am not having the same issue, although it does take a bit to calculate. Is there a particular driver that you recommend as stable? Maybe that's our issue.

Thanks

[Muhammed_Hamed]

Hey Streetwise

Sorry for the delay, we upgraded the recommended driver to 512.59 it works very well with V-Ray GPU
You can Email me the scene muhammed.hamed@chaos.com I will take a look and report back

The team member that is having the issue is on V-Ray 5 Update 2.3 and a driver of 471.68

Yeah, the new drivers fix some issues related to Geometry artifacts. This fix is on 495.xx drivers and later
This doesn't affect Cuda mode

Let me know if using the new drivers solves the issue

Best,
Muhammed