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Rendering with Arnold in CINEMA 4D using the C4DtoA plug-in.
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C4DtoA twin 3080ti cards.....

Message 1 of 4
129 Views, 3 Replies

C4DtoA twin 3080ti cards.....

I've recently built myself (had built for me lol) a machine with 2 3080ti's inside.
According to the Arnold documentation it should take full use of both cards whether they are V-linked or not (these cards don't V-Link). If they were you would get the combined memory but that's about it according to the documentation I read before going for this build.
The reality is that frame that takes 40 seconds with two cards only takes about 42 seconds with just one of them.
Over in Octane or Redshift the result of using both cards is a doubling in speed.
I don't really wanna go to either of those but I often have to render 4-5k frames for music videos so if I cant take advantage of my cards I might have to. Has anyone else experienced this?
Are Autodesk aware and is there a plan?

Message 2 of 4
in reply to: leegingold

NVLink will allow Arnold to render faster when there's significant communication between the two GPUs. Currently Arnold has some places where data is moved back and forth between GPUs and that can hurt performance if you don't have an NVLink. Roughly speaking, you'll notice this slowdown most when the amount of time spent per pixel sample is low. As the per-pixel-sample time gets more expensive, this communication issues has less of an impact and you can get good scaling.

We are working on re-architecting this area of the code so that hopefully a future version of Arnold will scale to multiple GPUs without needing NVLink.


Something to try until Arnold fixes the scaling issue: Can you render two frames at a time? So one GPU renders one frame and another GPU renders another? That might give you the same speedup you're after.

Message 3 of 4
in reply to: thiago.ize

Hey there. Thanks for your reply. That makes sense and I like the sound of
your potential solution. I'm not aware of a way to split a render up like
that but if it's possible that would certainly be a solution. I'm rendering
lots of frames as opposed to needing a single frame quicker. Is there
something you could point me towards that outlines this process? Thank you
Message 4 of 4
in reply to: leegingold

It's a bit complicated, but you can run two instances of Cinema 4D and start a render from both in parallel. One instance would use only the first GPU, the other instance the second GPU (see Manual Device Selection in the render settings). To do so, you have to have two Cinema 4D installs (e.g. duplicate the Cinema 4D folder).


Another option is to export your scene to ASS files and render via kick from the command line. One kick process using the first GPU, another kick process using the second GPU.

// Peter Horvath
// C4DtoA developer

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