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Dual RTX 3090 / RTX 3080 severe hit in performance

Message 1 of 41
3068 Views, 40 Replies

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?


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Message 21 of 41
in reply to: thiago.ize

Thanks for the update Thiago, fingers crossed.

We have a few more licences that use CPU atm, but want to move those to GPU as well. We're still need a few weeks to set up the new workstations, we're okay for a month or so.

Message 22 of 41
in reply to:

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, 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

Message 23 of 41
in reply to: thiago.ize

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

Message 24 of 41
in reply to:

Hey Thiago,

just checked the update, still the same issue. We've managed to source an identical 3090, so we have 2x3090s in our workstation, still no luck.

Do we need NVLINK to make Arnold work with multiple GPUs? I have no other ideas what could possibly be wrong...

Message 25 of 41

Hi Chris,

Could you post a screenshot of the following command when rendering on two GPUs and rendering on a single GPU ?


I am curious to see if both GPUs run at full power to rule out a specific issue, though if you say it works fine on other renderers it should be OK.

NVLINK is not required to run on multiple GPUs, we are still investigating bugs reported specifically when using multiple Ampere GeForces.

Message 26 of 41

Hi Adrian,

sure, here you go! Actually it looks like neither GPU is working in dual mode (actually one of them at 8%)

Single GPU works fine, manually selected works at 100%. All the other renderers work fine - V-Ray and Redshift.

Let me know if you need more help, would love to resolve the issue.

Single GPU


Dual GPU


Message 27 of 41

Interesting, it looks like when rendering on both GPUs, they stay in a low power state.

Can you try running nvidia-smi when rendering on the other GPU only ?

Message 28 of 41

Here you go Adrien, GPU0 selected manually. Yeah, kinda strange for sure.


Message 29 of 41
in reply to:

Actually, if you check the processes, when GPU0 is rendering, hick.exe is not active. If we use GPU1, hick.exe kicks in - also in dual GPU mode. Not sure if it's the way it should be, but that's something I noticed.

Message 30 of 41
in reply to:

If you run dual GPU with another renderer that does scale to two GPUs, what does nvsmi say? If it has both gpus running at near 350 watts, then this suggests more strongly a software bug.

Message 31 of 41
in reply to: thiago.ize

Hey Thiago,

screenshot attached, did a quick test, both GPUs running with Redshift - not at full throttle though. Not too heavy scene, shall I set up another?

Let me know what you think!


Message 32 of 41
in reply to:

Those were at 71 / 78% utilization and about 260W each. If you can get it to near 100% GPU utilization like Arnold or near 340W each, that would be good.

It's possible that the combined 520 watts used was still within the specs of what your cables/psu could provide but arnold's 680W need was too high?

Message 33 of 41
in reply to: thiago.ize

I'll run some benchmark scenes for Redshift and V-Ray. I'm sure it's not a PSU issue, 1600W in every workstation.

Will update you in a few mins.

Message 34 of 41
in reply to:

V-Ray standalone benchmark, both at 100% max is around 345W for each.capture.jpg

Message 35 of 41
in reply to:

OK, sounds like it's not the power feeding the cards. Thanks for testing that out. I think this will have to wait on us getting a pair of cards to test with. Sorry for the delay.

Message 36 of 41
in reply to: thiago.ize


Managed to source an NVlink and it looks like with the NVlink installed, the second GPU kicks in as well (HtoA Works on Windows and Linux as well.

Single GPU utilization is close to 100%, but dual GPU is only around 45-50% for each. It looks like the NVlink helps with initializing the second GPU, but splits load into 2 GPUs.

Let me know your thoughts!

Message 37 of 41
in reply to:

Weekend update.

I only had a few mins on Linux, but it seems the new update works fine, both GPUs utilized - Nvlink installed.

Will do a few more tests, but it looks like we’re back on track!

Message 38 of 41
in reply to:

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 ( 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.
Message 39 of 41
in reply to: thiago.ize

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.

Message 40 of 41
in reply to:

Hi, we just released a new version of Arnold (core version 7.2.5) and associated plugins which improve multi-gpu scaling. Let us know if this helps/hurts wirth your multi-GPU scaling issues.

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