project lavina with 2 gpus one 3090 and one 2080ti

[s.riegas]

Project lavina runs slower when combining a 3090 and a 2080ti than with just the 3090.
Can someone explain why this is happening.

[vladimir.nedev]

Can you tell us how much slower it is running for you ?

What's the FPS in both cases ?

Greetings,
Vladimir Nedev

[s.riegas]

thank you very much for your fast reply.
I used as well right now 2 3090s and i dont see any boost on the performance.
The way i consider performance is how fast without any denoiser it cleans the image.
Is this correct?

What can be the bottle neck?
I am not using nvlink, just two gpus.

[vladimir.nedev]

When you use two GPUs, rendered pixels (including additional denoising data) have to be transferred to the primary GPU.
This takes a fixed amount of time which depends on the resolution.

If you are running at a very high frame rate, this additional moving of data can cap the frame rate to a lower value.
If you increase the scene complexity and FPS drops, this fixed overhead will take a smaller percentage of the overall work
and you will see a bigger improvement.

However, I am not sure that's what's happening for you.
That's why I asked you about the FPS reported in the lower right corner in both cases.

Also, are you sure Lavina is using both GPUs ?
This should be indicated in the lower right corner as well, something like "2 x nVidia GeForce RTX 3090".

Greetings,
Vladimir Nedev

[s.riegas]

Dear Vladimir
Yes Lavina sees both gpus.
I am testing in an interior scene of BBB3viz called swedish flat.
Unfortunately is realy difficult for me to understand if i get a boost in performance when using second 3090, cause fps changes constantly while moving in the scene.
I work on architectural visualization and my expectation would be that i should be able to render an animation much faster when adding a second 3090.
Is there any benchmark for lavina as there is for vray gpu? I just did the benchmark on vray 5 gpu and second gpu almost doubles the performance.
Is there a way i could see that boost in rendering an animation in lavina?

[vladimir.nedev]

The easiest way to check the FPS is to just load the same camera each time or check with the starting camera.

Or you could render part of your animation with 1 and then 2 GPUs.

You will probably not get 2x the performance in Lavina, because we've optimized it for better responsiveness.
However it should not be exactly the same either.
But I need more data to say if it's expected.

Greeting,
Vladimir Nedev

[s.riegas]

Dear Vlad
In your reply you recommend I first test my animation with one gpu and then with both and compare.
Is there a way that I disable my second gpu in lavina?
or should i unglug it?
Thanks

[s.riegas]

One additional question
When I add a second 3090 gpu, should i be expecting the image to clean up (without any denoiser) faster?
This is the performance boost I am seeking from a second gpu. both when navigating in the scene and when rendering an animation sequence.
Thanks

[vladimir.nedev]

Is there a way that I disable my second gpu in lavina?

Yes, although it's not very user friendly at the moment.
See this thread for how to do it : https://forums.chaosgroup.com/forum/...ice-for-lavina

When I add a second 3090 gpu, should i be expecting the image to clean up (without any denoiser) faster?

Yes, however it depends on several factors.
1. If you are already at a high FPS (80+) you might see very little improvement due to the overhead of moving the results between GPUs.
If you are at 20 FPS for example, you will see a much bigger improvement.

2. The way sampling noise is perceived means that you have to wait exponentially longer to see a noticeable difference.
So it might be hard for you to detect that the noise is indeed clearing faster.
The only way to be sure is to compare the FPS or the time it takes for the image to reach a certain noise threshold.

Greetings,
Vladimir Nedev

[vladimir.nedev]

I forgot something very important.

If you are rendering an interior, the light cache can have a huge impact on the speed with which noise is cleared (at the same FPS).
Unfortunately, for now, we don't support the light cache when multiple GPUs are enabled.
So, in some cases, using multiple GPUs can lead to the sampling noise cleaning up slower (even much slower).

If you are rendering interiors with lots of bounced light from small but very intensively illuminated surfaces (like the sun falling on a small patch of a wall),
it might be better to enable just 1 GPU, in your case the 3090. A 3090 is roughly twice as fast as a 2080 Ti on its own.

Greetings,
Vladimir Nedev