GPU rendering significantly slower than realtime view

#1

Hi all, I had a feeling things have been rendering slower than I would expect for some time now since updating to 2024.3.

Here is a tennis racket being rendered, I have the setting to use 100% GPU on render, with the correct graphics card.

image
image.png1909×1170 174 KB

So here is my realtime view - about 5 seconds to get to 2500 passes:

image
image.png2041×1134 379 KB

But when rendering - at the same res as the realtime I get significantly slower results it takes around 2.5 minutes for 2500 passes

image
image.jpg1722×1069 213 KB

I honestly don’t know what is happening here… I do some renders where it seemingly renders at normal speed/GPU usage within the same scene.

#2

Hi Harry,

I think it is linked to the NURBS datas inside your file + Motion blur enabled. Remove all the NURBS from your geometries, in all model sets. It should help.

We talked about this kind of issue there:

and there more in detail about NURBS issue
https://community.keyshot.com/forum/t/bug-gpu-nurbs-motion-blur/11446/3

Best

1 Like
#3

Hi Pierre, thank you for linking me there!

Based on that post I tried the following:

  • Re-tessellating all objects and rendering to no effect
  • Removing all objects and re-importing without Nurbs to no effect
  • Removing motion Blur on the no NURBS import - render took 5 seconds rather than 2.5mins
  • Removing motion blur on original file with NURBS - render took 5 seconds

This looks to me like a motion blur bug.

I understand that motion blue is more taxing, but my preview window still out-performs the render with blur a crazy amount, to the point I will scrap the original render idea and go with something else as I had planned this to be a motion blur animation.

I don’t have the technical knowledge to know what’s going on, but if it was purely an issue that its a harder image/animation to render I would still expect my GPU to run at ~100% not drop to ~17%.

I can see in the next update this is due to be fixed from the second link you sent so I will try motion blur again on the next update (unless I have missed one but in the check for updates it says there is no new updates - I’m running 2024.3)

#4

Hi

There is another bug when MB / planar Light / hide event are combined or something linked with them. I’ve made a post a couple of month ago where I explaned what I’ve tried to find a workaround but without solution. Do you have curve animation node on Lights or similiar in your scene ?

Anyway you got the point, it’s linked mainly to the motion blur.
Your GPU workload is an interesting point to explore by the way, thanks.

1 Like
#5

Hi Pierre,

In this scene I am only using environment lighting, again it does seem to get slow for me at the moment when using physical lights - but I haven’t checked that in a similar manor to the motion blur. I did have a hidden spotlight which I deleted to test for you quickly but that didn’t make a difference to the issue. I have a lot of labels and opacity masks but no cure animation nodes or anything to do with a material animation.

However, what I did have was an environment rotation… I just unchecked that to test and it dramatically increased the render speed. On my scene with Motion Blur and NURBS it took 10.9 seconds for the 2500 passes this time.

Without Motion Blur but keeping the environment rotation on is good, but with the addition of the blur it drops - so yes it does seem to be linked to the light animation of sorts.

EDIT: I also just checked now with the environment rotation turned off, my GPU is now back rendering at 100%

EDIT2: Picture of PC performance with and without environment rotation active during an animation render:

image
image.png898×895 79.9 KB

#6

That is extremely weird. Great find. I will pass it on to our developers immediately!

1 Like
#7

@harry.wills Could I get you to try our 2025.2 Beta? Our developers have found an issue that could explain the behavior you’re seeing and fixed it in 2025.2.

#8

Hi Jan, sure I’ll download the Beta and test. I’m in the office today without that specific render scene but I will see if I can replicate it, if I can’t replicate it I’ll test the original scene later tonight or tomorrow for you.

1 Like