SLI GPU vs 3950X render results - maybe a point of interest

Started by Jet3D, May 05, 2020, 10:17:12 AM

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Jet3D

Hi guys and ladies,

I thought I would share my results for testing KS 9.3 on a test bed system.
I am conducting tests for work during lockdown...

This may all be common knowledge, (I don't visit much) however, I thought that I would share as it may help others.
Amazing work, Keyshot team. GPU rendering crushes the CPU results -  I can't wait to see two or more GPU's harnessed for speed.

DerekCicero

Good stuff. Do you have NVLink (it seems to show it on the right)? KS 9.2 and above support NVLink.

DriesV

For this scene in KeyShot 9.3, with NVLink, you should be seeing a nearly doubling of speed when using two cards instead of one.

Are you sure SLI is configure correctly in NVIDIA Control Panel ('Maximise 3D performance')?
Are you sure both GPUs are selected in KeyShot ('GPU Usage')?

Dries

Jet3D

Hello Derek,

To answer your question - yes, the cards are NVlinked via an ASUS bridge.

Jet3D

DriesV,

Yes in the Nvidia panel - it is set to maximum with both cards in SLI.
I tested many time with this enabled and disabled.

I will test again but, I am certain GPU usage was selected. I will return and let you know in an hour or so.  8 )

Regards, Jet

Jet3D

Update with a five second speed difference. Same settings - not sure what changed unless it was a background task.....
Not a great increase - your thoughts?

DriesV

Maybe the rendering is just too fast? :)
What results do you get with, say, 1024 instead of 256 samples?

Dries

mafrieger

Quote from: DriesV on May 06, 2020, 12:20:50 AM
For this scene in KeyShot 9.3, with NVLink, you should be seeing a nearly doubling of speed when using two cards instead of one.

Dries

hmm just a question:
whats the technical background for doubling speed in this case?

when asking whats for "what's NVlink good for?", the answer
was "only doubling memory"
QuoteNVLink will not double speed though. It is not a magical solution with linear performance scaling.
please see https://forum.keyshot.com/index.php?topic=25847.msg108674#msg108674

were there big changes regarding this when moving from 9.2 to 9.3?




DerekCicero

Dries can provide additional detail on Monday, but I believe the answer is that is when the memory stays under the individual card threshold, performance will double, however once you pass the threshold on one card (say 8GB), normally it would throw up an "Not enough memory" warning , but with NVLink, it will kick over and pool the memory on the cards (now 16GB) so you can do the render, but at that point you lose the doubling effect b/c the cards have to switch to the process the memory sharing, swapping all the textures, etc.

Jet3D

These are 11GB cards so, it would have a total of 22GB.
We have some Quadro P6000 24 GB cards at work. I will test with these when lockdown lifts.

I have been CPU rendering and if I had only tried GPU at some stage - 95% of the time, I would never go back.

After what I have seen that KS 9.3 can do - I will be steering work into using KS in the future. Perfect for what I do and able to deliver fast results in the film industry that needs everything yesterday! LOL.

DriesV

It seems like you are able to render the scene on a single card. In that case, performance should nearly double with two cards.
What I said in that thread was just a heads-up that you shouldn't expect double performance in all cases.

You don't happen to be able to share the scene, do you? Then we could check internally.

Dries

DriesV

In hindsight, are you actually sure you are just rendering with a single card? Turning off NVLink doesn't mean that you can't use both cards in KeyShot. It just means that the memory won't be pooled, as Derek outlined.
Enabling NVLink will not do anything for perfomance. It just allows you to fit larger data sets in both cards.

Dries

mafrieger

Quote from: DriesV on May 10, 2020, 02:12:54 AM

What I said in that thread was just a heads-up that you shouldn't expect double performance in all cases.


Many thanks for clarifying this !!

Some questions regarding usage of GPU's VRAM:
1) what's biggest VRAM amount needed for a scene you have seen so far?
2) What are the things that drive VRAM amount up most?
3) Could you share a demo scene with very big VRAM needed?
With this one (jet3d an others) could see if a / a couple of Quadros with losts of VRAM is worth it / needed (in real live)...

menizzi

I must be doing something wrong. My gpu renders are really really really bad. 100%  unusable bad. as in so bad I bought a lic for octane standalone and i am trying to learn that but i have not had much time.

Maybe in Version 10? If you click the Denoise button watch out its so bad it makes me cringe. I also have a 2080 super.

DriesV

Quote from: menizzi on May 10, 2020, 09:14:16 PM
I must be doing something wrong. My gpu renders are really really really bad. 100%  unusable bad. as in so bad I bought a lic for octane standalone and i am trying to learn that but i have not had much time.

Maybe in Version 10? If you click the Denoise button watch out its so bad it makes me cringe. I also have a 2080 super.

Let's try to break your issues down.

What kind of scene are you trying to render?
Is it Denoise specifically that is bad?
Can you pinpoint the issues you are running into?
Can you share your problematic scenes perhaps?
What is it you think Octane will/might do better than KeyShot?

Let's try to be constructive and find a solution. :)

Dries