Utilization of different generation GPUs

I am in the process of building my new workstation. I will definitely get RTX 4090 and another GPU to be connected to the monitor.

My question is:
Can USD Composer efficiently utilise both GPUs , even if they are from different generations? I am thinking of getting either RTX 3090 or RTX 4070ti.

I am aware that they will not have same memory pool. Performance wise I would prefer to get 3090 but I am concerned about the lack of dlss 3 support in Ampere card.

Have a great day everyone!

Honesly I strongly advise against a second gpu unless they are identical. The phrase you used “another gpu connected to the monitor”. That is not a good idea. The gpu “connected to the monitor” is your PRIMARY gpu. It is the most important gpu you have. Do not discard it for a secondardy gpu. The gpu that is connected to your monitor is the main gpu for all of windows, for all apps, all systems. That should ALWAYS be your best gpu. Without exception.

Secondly getting a second gpu that is less powerful that your first, is not always beneficial. You really are better off sticking to one, or two identical. The reason, to answer your question is that Composer, like any multi-gpu system will always be forced to use only the amount of vram in the lowest card, because the scene must fit into both cards gpu. So if you have a card with 24GB and a card with 12GB, as soon you engage them both, composer is automatically limited to 12GB. So this is why I say, stick to one incredible card, or add another identical card. If you must add a second card, non identical make sure it has the same vram size.

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Hi Richard! Thank you for your answer.

My idea of 2nd (less powerful) gpu that drives the monitor is coming from V-Ray where this way I have all the 24gb of 3090 available for rendering instead of loosing at least 4gb if connected directly to the monitor. Monitor is driven by 2060 SUPER and I don’t use it for rendering.

So far I’ve been using the Composer with this setup, and I set the RTX 3090 to be specifically used for the Composer via Nvidia Control Panel and I think it worked well so far.

In the viewport I see only the RTX 3090 with its 24gb of VRAM listed and it is the only one being used for render when I check the GPU-Z .

From what you have just said this solution is not supppose to work properly, am I missing something?

Your logic and setup is sound, yes. If you have gone into the control panel and done that, and it works well for you, then good. My advice in general stands, but if you are forcing a re-direct for apps to use a secondary card, and it is stable then great. Glad to know that works. However, without the nvidia control panel re-direct, yes it would be a different story.

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Thank you Richard!

Although, the question remains if in case of mixing two different generations, I might have some issues with let’s say with the denoising capabilities?
Given the fact that Ampere does not support dlss 3 and the RTX 4090 will.

I am asking because I have seen the New (Experimental) denoiser in Composer and I wonder if it has anything to do with DLSS3 / frame generation techniques.

Yes exactly. We have DLSS3 features that are hardware specific for the 4090 and Ada A6000 cards.

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Thank you!

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