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Chris Ferenczy avatar image
Chris Ferenczy asked ·

Dual RTX 3090 / RTX 3080 severe hit in performance

Hey Everyone,

managed to source a 3080 and a 3090 for my workstation and thought I'd give Arnold a try in Houdini. To my huge surprise, using both GPUs are not helping but rather slowing down rendering A LOT, I have to manually select a single GPU to have decent performance.

Tried Windows 10 and Ubuntu 20.04 with 5.4.1 demo, same issue, no love. Could anyone shine some light on what am I missing?

Thanks!

gpuhtoa
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We haven't been able to reproduce this. Does this happen for all scenes? Can you make this happen with a simple scene that would be easy to share with us?

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Actually scene is as simple as a sphere and a plane with a skydome. Tried latest Nvidia Game Ready and Studio drivers as well, Windows and Ubuntu, nothing helps, same issue.

Let me know if you need a screen share so you can see what's going on!

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If you can post the scene here that would help.

If you know how, ideally export it as an .ass file, double check you can reproduce the speed differences using kick, and supply the debug level logs (-v 6) from the 3080, 3090, and 3080+3090 renders. Otherwise, upload what you can along with debug logs from running in htoa.

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We were unable to reproduce a slowdown on a dual 3080 using arnold 6.1.0 and 461.40 driver. We are wondering if maybe it could be a hardware issue, such as a GPU being plugged into a slower PCI slot? Using the latest arnold (6.2.0.1 as of right now), could you try:

  • a single and dual gpu render with display turned off (in kick it's "-dw"), to see if that fixes/reduces the slowdown. In our testing we saw a small speedup with this, but I'm curious if for you it'll give you a big speedup as this minimizes a bunch of communication between CPUs and GPUs.
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Tried kick -dw and it speeds up render times when using Windows, not too crazy, but a bit of an improvement. Issue still persists in Windows, GPUs are not fully utilized.

Latest version works great using Pop OS and NVlink added, both GPU fully utilized. I assume it's not a hardware issue for the reason it works fine with Linux.

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Stephen Blair avatar image
Stephen Blair answered ·

We think this is a bug, and we're working on confirming this (eg getting the right cards for a test).

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Thanks Stephen, appreciate your help!

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Just updated to the most recent HtoA and the issue is still there. Is there any progress you could share Stephen?

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We're working with NVidia to get test hw setup, I will check in and see how that's going...

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Thiago Ize avatar image
Thiago Ize answered ·

While we weren't able to test with your particular GPUs, we think there's a chance this might be fixed in the just released 6.1.0.1, thanks to the below bug fix. Please let us know if this build still gives you issues.

core#10231 [GPU] Texture and exception handling errors using multiple GPUs without NVLink

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Thanks for the update Thiago, unfortunately still no love. Same issue, tested both Win and LInex. Fingers crossed for next update.

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Thiago Ize avatar image
Thiago Ize answered ·

We had one user report similar problems with two GPUs rendering arnold several times slower than one GPU and this is how they solved it. Worth a try?

Apparently SLI needed to be turned on in my Nvidia Settings but it was NOT there. I tried plug in my monitor in the GPU 0 Slot 1 and magically SLI setting showed up! Apparently that's a requirement. Must have monitor plugged into Card 1 to get SLI to appear...
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Thanks Thiago!

The reason it will not work for us is that the RTX 3080 has no SLI/NVLINK, so the option won't show up in the control panel - we'd need to have 2 identical 3090s to have the SLI option enabled.

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