GPU Rendering Slower Than Realtime - NVidia RTX 3090 ti

#1

Hello -

First:

Processor AMD Ryzen Threadripper 2990WX 32-Core Processor 3.00 GHz
Installed RAM 64.0 GB (63.9 GB usable)
System type 64-bit operating system, x64-based processor
GPU RTX 3090 ti (driver v566.36)

Keyshot v2024.3

So, I am trying to render an animation and have been chasing a frustrating issue with GPU rendering much slower than real-time – what took Keyshot 40 seconds to resolve to 512 samples in real-time took 3 minutes 10 seconds when rendering. So, for the scene in question, it would take 12+ hours for what should take around 2.8. It doesn’t matter if I select “Use Real-time GPU Usage” or not in the output window.

I have tried 3 different drivers for the RTX 3090 ti dating back to September 2024 (clean installs, one with DDU). Finally, in the scene mentioned above, I randomly deleted an unused model set out of desperation and befuddlement, and suddenly the renders were taking the expected 40 seconds to finish. Not a solution, but I’ll take it.

Now, in a related scene, the situation is back, though not as bad – it is taking 70 seconds to render what takes 40 seconds in real-time. So, what should take 2.3 hours for this particular sequence will take 4.1 hours, which in production and under deadline is far from ideal. I have opened a ticket with support, and so far the only recommendation is to roll back the NVidia driver which, as mentioned, I have done.

Has anyone else run into this issue or even better, does anyone have a solution or some thoughts on a possible solution?

Thank you!

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#2

If your real time window is smaller than the output res, the realitime window will render faster. Fewer pixels. Also check your DPI settings in the Still Image tab of the output window. We render at 300 dpi for print, and when I do render for an animation (doesn’t happen often) that’s one I forget to check.

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#3

Thanks, @matt.gerard -

Real-time and render output are the same resolution. I haven’t thought of checking DPI, though. I’ll give that a go. Thanks!

#4

Hi Matt,

If resolution are the same, DPI should not make any changes in the final output as pixel number will be the same.

A 300x300 pixels render at 300DPI or 72 will stay a 90’000 pixels image to compute. DPI render input is a cool tool to know how big your rendering will be printable without quality lost or if you have a print size target to reach without making the conversion from pixel to cm.

I’ll be really surprised if that makes a difference in rendering time. If so, please tell me.

Thanks.

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#5

@dan.spore I had the issue with the same KS version and reported it as a bug. A workaround which worked for me was loading the scene into KS and reload it immediately again. Every first time I opened the scene it was slow as a turtle while second time everything went normal. Must say that the slowness also impacted the real time render view actually so not sure if it’s exactly the same. But it happened every single time with that scene.

About DPI:

I agree here with Pierre, dpi doesn’t matter. That’s also what I find terribly confusing if you export a GLTB from KS it asks about DPI. I don’t care, it’s screen and I only care about pixels. The DPI is just a parameter in the file format, you would only notice if you print images directly. If you place a 72 dpi image at 10% in Indesign for print it won’t give a different result compared to a 300dpi image placed at around roughly 30%. The information in the file is exactly the same.

#6

i have to keep reminding myself that DPI is just a scaling factor for how large it appears as 100% in InDesign. @72 dpi our renders show up huge, @300dpi our renders show up as 4x3" in the layout.

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#7

Well, you’re not alone. I would prefer to have all dpi mentions removed from KeyShot since they are only confusing. A digital photo camera doesn’t ask you how much DPI you want your image to be as well, it’s just pixels.

I think Will Gibbons made a nice cheat-sheet for the confusing dpi/resolution things :slight_smile:

#8

Hi @dan.spore

I’m facing exactly the same issue, with a RTX 4090.
Resolution 1920x1080, 30s to reach 1’000 sample in realtime view then 10 minutes in the render window. I enabled motion blur and I guess it’s why the gap is much more important than you.

image

Did you find why and/or a workaround ?
Best.

#9

Did you try simply saving the scene and reloading it using recent files?

#10

Hi Oscar,

Yes I tried that after reading your previous message, no changes. Same if I import the file in a blank file.

I had a couple of critical error with ‘bad triangles’ after switching back to CPU, but I had to kill KS process because it was not responding. Back in the scene I tried to re-tesselate all the parts, but no changes.
I’ve tried to delete all parts/animations/lights/studios/cameras/environments to keep only 1 main geometry with basic plastic material and 1 basic environment and I still have quite strong differences between realtime (which I found quite slow regarding the ‘empty’ scene) and render windows. A strange thing was that KS still shown me an ‘actualise displacement’ icon on top right corner like I still had a geometry somewhere with displacement material.
In the color mode, there is still many colors in the swatch although there is only one material which not uses named colors. Maybe a point ?

Another weird point is later in the animation, at least after frame 501 where I rendered a first image range previously, the gap drop to a bit less than twice the time, and I can render a frame in 1 to 2 minutes (which is much more acceptable for my deadline).
Models are the same with same materials, only physical lights changed.

#11

I’m almost sure you did but you also tried the September 2024 driver from Nvidia?

Difficult to guess what the issue is, I’m also quite sure you don’t put in a HUGE resolution by accident?

edit if you want/can I can try the scene here to see what happens with my 4090 and config.

#12

No I didn’t change driver’s version, and I’ll not have time for that exploration. Maybe Monday if issue still makes me crazy. I’ll render the animation’s end first and the begining where the bug is the strongest then and hope it will be finished monday. I don’t really get how to install previous nvidia drivers.

I cleaned all my file with duplicated material, duplicated color swatches, unused color modes but no changes.

No, resolution is 1920x1080px.

It will be complicated for me to share that client file as the product isn’t on the market yet. Thanks.

Sometimes I get this error, it should be linked I guess but no idea how to fix that.
image

In another hand, I often have the ‘gpu setup’ window infinity loop when I close the rendering window, and I must kill and restart the KS process to get my scene back.

Best.

#13

Reason I ask about the driver is that the actual recommended Nvidia driver is still the one from September 2024. I had a scene where first 150 frames rendered fast and than suddenly it slowed down like crazy. That was solved by installing the older drivers.

It’s not much work, just go to Nvidia.com/drivers and download the old studio driver from September. There’s a link on that page pointing to the older ones.

Than just double click the installer and if it installs say you want a custom install. Just select the drivers and not the Nvidia app/GeForce experience. And select the button clean install after a minute or five it’s done.

Worth trying is you have so much issues.

#14

@pierre.kairn I looked for direct link for that driver for you but Nvidia site gives a internal server error, saw I had it still in my downloads so if you want, I uploaded it here:

#15

Thanks, I’ll try it monday if rendering isn’t finished as I’m not at work for the week-end.
I’ve tried this afternoon to install an old driver but it was stucked at the hardware compatibility window … Let test this new one monday

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#16

Hi @oscar.rottink

I’ve tried your driver, and it’s worst. GPU crashes at the render window opening.
I’ll try another driver if it could changes something.

#17

Hi @pierre.kairn,

Really odd, reason I suggested it was because I had render speed suddenly reducing in the beta as mentioned here: 2025.1 Beta | GPU Render in background - For Beta Testers - Luminaries

When I switched to the Sep 2024 driver it didn’t drop the render speed anymore.

If your client is ok I could render some frames just to keep some progress (if it works here)

#18

Hi Oscar,

Thanks for your time.
I think I found something connected to NURBS rendering.
I’va made a blank file, imported my STEP model and realtime was fast and final slow. I deleted some parts and gap went smaller as I deleted more parts. > It isn’t linked to a specific part.
In another file, I imported the model, unchecked the ‘import nurbs’ box this time and I didn’t notice speed reduction, rendering is even faster. (realtime : 10s > 4’200samples vs final render 10s > 5’200s)

I guess KS is bugging and uses NURBS data in the final rendering even if that is not checked. Which could make sense.

@dan.spore Can you tell me if your file had NURBS file imported ?

Thanks.

#19

If I look at the top screenshot of Dan it sure does look like he has nurbs imported. I know there’s a GPU limitation with Nurbs like:

  • NURBS: NURBS-only objects will be ignored in GPU mode. Objects that have both triangles and NURBS data, will be shown as triangles.

But that shouldn’t give weird render times. Would be an interesting one for the developers I think to look into. If I’ve some time I’ll check if I can create such a scene as well.

#20

I remember I had some complications with the STEP file from my client, with surfaces errors, even when I imported it inside Rhino or Solidworks.
Maybe it’s something between KS and the file.
I’ll re-importe my file without NURBS in my final scene and check if I still have speed reduction.

I’ll ask my client if I can share the file to KS for developers.

EDIT : First : Classic imported model, with NURBS included.
image

Second : I clicked ‘remove nurbs’ in the model’s menu in the scene tree. No NURBS in the file
image

Third : I duplicated the model set with the nurbs, removed them in the first one, disable the NURMBS’ one. No NURBS visible, but NURBS in the file. Render seems to be impacted by NURBS from other model sets, even if they’re disabled.
image

For each tries, I set a rotation on the root model and motion blur at 1/50s for camera and parts.

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