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Brian Hanke avatar image
Brian Hanke asked ·

Arnold GPU is slow and noisy

What's the deal with Arnold GPU? Cycles GPU in Blender is 2-4 times faster on the same scene. GPU-only renderers are extremely fast. But I can't get any speed improvements with Arnold GPU. Almost without exception scenes render slower and end up noisier when using GPU mode. Am I missing something? I've messed around with adaptive sampling but it doesn't seem to make much difference. I'm using a laptop with a 6-core i7 and a 1070. I've attached two renders: 3m23s CPU, 4m10s GPU. CPU looks beautiful but the GPU one is FAR noisier. CPU was at 8/2/2/2 and GPU was 20AA (no adaptive sampling).3m23s.png

4m10s.png

gpu
3m23s.png (1.1 MiB)
4m10s.png (1.3 MiB)
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Thiago Ize avatar image
Thiago Ize answered ·

Shaders with refraction and reflection are known to be noisier on the GPU than on the CPU and so will require more samples to converge. Are you finding that GPU is slower in scenes that aren't all just glass-like like in your shader ball example? If you change the shader ball to not be transmissive how does it compare?

Finally, what version of mtoa/arnold are you using? Try to update to the latest (arnold core is at 6.1.0.1 as of today).


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Brian Hanke avatar image
Brian Hanke answered ·

> If you change the shader ball to not be transmissive how does it compare?

Wow, big difference there. Changing the material to be only diffuse and spec really let the GPU shine. 6:55 for CPU, 2:02 for similar noise level on GPU, 3:13 and it's substantially cleaner than CPU. Very nice! Much more what I expected from a GPU renderer (50-75% faster).

I have the most recent MtoA and Arnold versions. Are there any plans to improve Arnold GPU performance on glass/SSS materials?

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If you mean the converging of noise, then yes.
This is an ongoing process, and it's not a quick fix.
If you see render engines that handles these things faster, it is very likely they are more mature, or they fake/cheat, do things that eventually will sacrifice quality in one way or the other.

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