GPU Hybrid Rendering Slower than CPU Alone?

[ValeroStudio]

So have a this simple test scene and I ran a rendering using CPU alone and it's render time was 3m 3.2s and then ran the same exact scene with GPU Hybrid and it's render time was 7m 27s

I was kind of shocked really. Should GPU be faster or at least in the same ballpark?
Intel i7 7700 4.20Ghz
32GB Ram
GeForce GTX 1080

[konstantin_chaos]

Hi Matthew,

There is one things to consider here:
The progressive rendering process is done in passes - each pass more detailed than the previous one - based on a noise threshold value.
Note: V-Ray will never end / stop a render in the middle of a pass since there will be inconsistent sampling in different areas of the image.
The GPU engine is setup in such a way that it takes a lot more samples during each individual pass.
And in some situations the last pass done by the GPU can surpasses the target quality, but V-Ray can't cancel the pass - it has to finish for a usable image.
As a result the render time when using the GPU engine is longer but at the same time the quality should be better.
This is often times the case when the render time is short.

Additionally, which devices have you selected in the GPU list?
Are you using just your card or the CPU as well?

I'd also appreciate it if you can share the test scene you're using so that we can benchmark it here.
It's always possible that we have not set the ideal internal parameter values of the engine.

Regards,
Konstantin

[ValeroStudio]

I have both the GPU and the CPU selected in devices list. I will send you a link to the scene.

[ValeroStudio]

Rendering with progressive turned off did render faster but with a lot more noise using the same settings as the CPU render.

[Peter.Chaushev]

Hello, Matthew,
Thank you for your report!
There is an ongoing investigation of the issue you've stumbled upon. Until the a permanent solution is available, for now you can resolve it by enabling the Sunlight in your scene.
Will post again once the cause is identified and a fix on the way.

Kind regards,
Peter