Less GPU more speed? A Render test.

[Micha]

I need to render a simple product animation and checked the speed per frame (progressive, 1920x1080):

2x2080ti+3090 ....14.3s
single 3090 ... 13.5s (RTX15.5s)

Best speed I got by single 3090 and bucket mode - 11s.

Is it not strange, that additional cards slow down the calculation?

[piotrus3333]

Im guessing one of 2080 is running displays?
if so try 2080+3090 or run displays on 3090 and render on all 3.

[piotrus3333]

also check whats happening with gpu-z

[Micha]

The 3090 is used for the display, since so the large VRAM allow to use all three cards until 11GB.

What could I see at GPU-Z?

[piotrus3333]

clock speeds and usage %.

[Micha]

I checked the usage and found, the single 3090 works much stronger than in multi GPU mode (the middle peak of the the three at my screenshot is the single GPU rendering). If all GPU are running, than the 2080ti are running good, but the 3090 is slowed down.

It looks like multi GPU doesn't work well for light scenes. So, an animation can't be pushed to shorter render times of a few seconds by using more GPU. But it helps to buy one most powerful GPU and use only this.

[piotrus3333]

how does the usage looks on 2080s?
something clearly not working right.
you are using gpu LC or BF+BF, right?
how is the performance on 2x2080 so the card running displays is not used at all for rendering?

[Micha]

I use CPU LC since GPU LC isn't available at V-Ray for Rhino yet.



I did an other test BF+BF and progressive:

3090 + 2x2080: 16,7s
3090: 16,5s