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I have a question about multi GPU rendering with cycles.

Recently I installed a RXT 3080 in my system alongside a RTX 2070. Things work fine on the system with them. One of the reasons I wanted to use both was to have faster render times in blender. Doing so I noticed a few things and I was wondering if anyone could shed light on it. The following is the render times for the scene shown below at a resolution of 2000px X 1000px:

enter image description here

RTX 3080 Only- 00:39

RTX 2070 Only - 01:02

Both GPUs - 00:40

CPU Only(AMD Ryzen 9 3900X) - 01:31

GPUs + CPU - 01:58

The idea I had was that if I use both GPU's it should be fastest, but in this case there is virtually no difference compared to just using the RTX 3080 by itself. And what surprises me also is that if I combine things with the CPU it makes things slower.

Thanks for any help in shedding a light on this for me.

rangerx
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  • Just a guess, but since two GPUs cannot work on one tile at the same time, and once the slower GPU’s working on the tile, the faster GPU can’t take over… see? – TheLabCat Oct 28 '21 at 04:10
  • In Preferences > System > Render devices what option did you select ? – Gorgious Oct 28 '21 at 06:49

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