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Arnold GPU - Rendering volumes (VDB)

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Message 1 of 4
am_wilkins
1252 Views, 3 Replies

Arnold GPU - Rendering volumes (VDB)

Good day,

 

I'm running a render test on a volume between Arnold CPU and GPU.

The render test is the VDB "Bunny" asset with a simple volume shader.


While the CPU rendered the frame in 24 mins, after 1 hour+ of waiting the GPU render was only on around 11%

CPU:
Sampling: Min AA 3, Max AA 12, Threshold 0.001
Depth: 3 Spec, 3 Diffuse, 3 Volume

Render time: 24mins

arnold_cpu_adaptive_volume_bunny.jpg



GPU:
Sampling: Min AA 10, Max AA 26, Threshold 0.001
Depth: 3 Spec, 3 Diffuse, 3 Volume

Render time: 1 hour+ render wasn't completed, only at around 11% (canceled the render test)

 

The reason for the increased Min AA is to prevent zero pixel values.

 

I lowered the sampling settings to try get a frame out.


GPU with lowered Settings:
Sampling: Min AA 3, Max AA 12, Threshold 0.001
Depth: 3 Spec, 3 Diffuse, 3 Volume
Render time:  64mins
arnold_gpu_volume_bunny.jpg

  1. I'm getting double the expected render time, even with lower sampling settings.
  2. We're also seeing what appears to be shadow artifacting under the volume.

 

Are volumes not very optimized for the Arnold GPU engine yet?

 


All the best,
Amwilkins

--

Houdini Core Version 19.5.534
Arnold Core: 7.2.1.0

HotA: 6.2.1.0

CPU: AMD Ryzen TR 3990x

RAM: 128GB
GPU: NVIDIA RTX A4000

 

3 REPLIES 3
Message 2 of 4
am_wilkins
in reply to: am_wilkins

Hi there, I did some additional testing.

I've managed to bring down the render time of the CPU Adaptive, however the GPU engine is still taking very long and the shadow artifact remains. Even with a higher adaptive threshold (tried all sorts of combinations) and the result is significantly more noisy.

I also reduced the "Density" of the shader (was a little too dense in the previous post)

 

I'm looking to:
1) Reduce Arnold GPU render times while still achieving a clean result
2) Solve the shadow artifact

CPU:
Sampling: Min=3, Max=12, Threshold=0.01
Depth: 3 Diffuse, 3 Spec, 3 Volume
Volume Step Size 0.1
Volume samples on light - 2 (default)

arnold_cpu_adaptive_volume_bunny.jpg

 

GPU:
Sampling: Min=3, Max=14, Threshold=0.05
Depth: 3 Diffuse, 3 Spec, 3 Volume
Volume Step Size 0.1
Volume samples on light - 2 (default)

arnold_gpu_volume_bunny.jpg

 

If you download and compare the images, the GPU render would need higher AA samples by almost double (or some lower threshold) to match the CPU render and then we'd be looking at 1 hour+ render times again.

And then, sorry to do this (hurts me too) but here's a Redshift comparison which I'm trying to compete with.

It appears like I have no chance of getting close to this render time with Arnold volume rendering.

redshift_volume_bunny.jpg

 

 

All the best,
Amwilkins

--

Houdini Core Version 19.5.534
Arnold Core: 7.2.1.0

HotA: 6.2.1.0

CPU: AMD Ryzen TR 3990x

RAM: 128GB
GPU: NVIDIA RTX A4000

Message 3 of 4
thiago.ize
in reply to: am_wilkins

Unfortunately, GPU volumes in Arnold are known to be slower than we'd like, so I'm not surprised, especially with your CPU, that CPU is faster than GPU. The artifact is likely one we are already aware of and is tracked in ARNOLD-13469. Both the artifact and performance we want to improve.

Message 4 of 4
66175545
in reply to: am_wilkins

I have a scene with elements that have VDB and other materials like diffuse, refraction, etc., but I found that when rendering with VDB, the GPU rendering output is very slow and not as fast as the CPU, so I'm eagerly hoping that the official can pay attention to this and optimise the speed of the GPU in the case of complex scenes with VDB. Because it is also urgently needed in production.ar_volume_test_16_cpu.png

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