Render times

[glorybound]

I have a pretty large scene that is rendering in an hour with CPU, but when I set it to Hybrid, the render time goes up to 1:45 minutes. I have a Titian RTX, with 24GB of RAM and the scene is taking up 13 GB of that. Why would my render times go up if I am using the same CPU power and adding the GPU to it?

[MANUEL_MOUSIOL]

Are you rendering progressive or bucket?

[glorybound]

I am rendering bucket

[Morne]

You are not "adding" the GPU to it
GPU (RT) is a totally different render engine to advanced CPU. When using GPU, they're cheating the code to make the system believe the CPU is a GPU. In laymens terms, when rendering GPU, it's accessing the GPU system via a more direct route, but when using the CPU to render GPU, it's using a translator to stop and ask for directions along the way.

Also, with GPU bucket, it's a relatively new(ish) feature that may not yet be as polished as progressive just yet

[glorybound]

Hu? It is using the GPU plus however it uses the CPU, so why would it be slower? I'll try progressive.

[MANUEL_MOUSIOL]

Yeah, bucket should be faster though... Strange occurrence

[^Lele^]

Not with the GPU engine, bucket isn't faster.
Will need more work, simply switching to progressive should get a big chunk of time back.
As to why it should be slower, particularly with buckets, it's because of the waiting around that needs to happen for buckets to be finished (with the GPU engine), as the CPU can't scamper off in the distance by its lonesome.

[MANUEL_MOUSIOL]

I thought bucket was faster because the GPUs dont have to wait for the CPU to send back what has been computed as in progressive. So in bucket mode every processor has its own area to care about... wrong?

[Muhammed_Hamed]

In my testing Bucket mode has been always faster than progressive on GPU, to get to the same clean result(unless you are getting stuck buckets maybe)
With bucket on GPU, I use .02 noise threshold or even higher, it is very sensitive to noise unlike using Buckets with the CPU engine, where I use .008 noise threshold and sometime lower than that.
For comparing the 2, make sure both your results are similarly clean as far as you can.
I haven't seen a case where hybird rendering is slower, mostly I have seen the GPU engine to be faster and deal with noise better than the CPU engine.
Would be nice if you share both your renders, there was a problem with fur on GPU recently. It used to to get stuck for 15 minutes or so on compiling Geometry, but this was fixed in the nightlies.

[Muhammed_Hamed]

Only case I have seen GPU buckets to struggle (get stuck) is on fur/hair with VrayHairNext material
But same happened with CPU engine, this is one of few cases I would use progressive over bucket.

[glorybound]

So, it's about 50/50 to which is faster. I tried GPU again and it crashes to the desktop, so I'll test things on another project.

[^Lele^]

So, it's about 50/50 to which is faster. I tried GPU again and it crashes to the desktop, so I'll test things on another project.

When with GPU, you are very dependent on the state of your video drivers, which can get messed up (not just because of V-Ray, mind you.) within the single OS session.
If you feel stuff is misbehaving, get yourself a hard reboot, and then try again.

[Morbid Angel]

gpu is fun

[MANUEL_MOUSIOL]

When with GPU, you are very dependent on the state of your video drivers, which can get messed up (not just because of V-Ray, mind you.) within the single OS session.
If you feel stuff is misbehaving, get yourself a hard reboot, and then try again.

I find that very disturbing . Indeed since switching to gpu rendering my 3ds max and computer restarts became very frequent.
do you think that will ever change? Or there might be a tool that checks drivers and tells me live when there is a problem?

[glorybound]

I updated my GPU to the latest driver and I no longer see the driver error message. Are there any issues with the latest drivers? I haven't experienced any, yet.