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Recently I have built a new workstation PC with dual GTX 1080 Ti. I know that in Cycles, each GPU renders 1 tile but I'm not sure about EEVEE. I tested it and it seems that even if I have checked both GPUs in user preferences EEVEE still uses only 1 GPU. I tried opening 2 instances of Blender 2.8 and set different GPU in each but the result was same; it keeps using one GPU only. This might not be implemented yet or SLI bridge might be required, I am really not sure. Do you guys have any experience with it? Has anyone done some rendering using SLI?

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  • $\begingroup$ I'm also curious with duel (non-sli) video cards have any impact on Eevee. $\endgroup$ – Jonathan Dunlap Jul 28 '18 at 23:26
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Multi GPU support for EEVEE is a really hard goal to atchieve because of the nature of the technology. It is not being worked on at the moment and it is not planned for any time soon. EEVEE might benefit from SLI or Crossfire setups. It would be logical to wait untill it's realeased to test that though. I believe it is safe to assume that EEVEE will definitely not be able to use multiple GPUs that are not connected with SLI/Crossfire for real time rendering when it is released or any time soon after.

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  • $\begingroup$ It's quite simple actually, you render frame1 with GPU1 while also rendering frame 2 with GPU2. That way animation render twice as fast. Unfortunately no one sees the benefit from such a simple idea. Maybe I will create a plugin and collect huge $$$!!! $\endgroup$ – Logic1 Dec 22 '19 at 9:09
  • $\begingroup$ I am really glad it is so simple for you. Let everybody know when your plugin is out. $\endgroup$ – Martynas Žiemys Dec 22 '19 at 10:21
  • $\begingroup$ Thanks, it's actually quite simple for anyone. I would imagine a python script that launches multiple instances of the currently loaded .blend and passes in some arguments (or a script) that sets up the headless Blender instances so they render a unique range of frames and each instance using an available GPU. In fact I'm doing almost exactly that currently but I had to do it manually. My render time is exactly 1/2 what it would be on only a single GPU. Have a nice holiday, cheers. $\endgroup$ – Logic1 Dec 22 '19 at 11:39
  • $\begingroup$ As far as I know you have to have the GPU connected to a monitor for it to render with OpenGL. How do you switch what GPU Blender uses for EEVEE rendering? Multiple instances don't sound real time to me either and they require more memory. Why don't you try SLI? There should be a speed increase with SLI. $\endgroup$ – Martynas Žiemys Dec 22 '19 at 12:20
  • $\begingroup$ I don't know about SLI, but I do know that the multi-instance approach for animations does utilize all of my GPUs allowing me to render (n)times faster. You can easily right-click on blend.exe to select which GPU will be used to render on: i.imgur.com/sHzHMal.png $\endgroup$ – Logic1 Dec 22 '19 at 12:38
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First of all, the Preferences settings where you can select which devices to use is a Cycles render setting only. There are no settings in Blender that will affect which GPU(s) Eevee is using. That depends entirely on which display Blender is started/active on.

It's possible to play games (on Windows at least) where you start one copy of Blender, then change the default OpenGL GPU to a second one and start a second instance of Blender and then you have two copies of Blender each with a single dedicated card for Eevee so you can run two render jobs in parallel for increased throughput.

Eevee does not currently (and may never) know how to utilize separate GPU devices the way Cycles can. However in SLI mode, two video cards basically become one, and I don't know for sure if SLI will currently affect Eevee performance (lots of people think it won't because "Eevee can't use more than one GPU" but I haven't found anyone who has definitively tested it!).

If you do have two cards in SLI mode, then I believe Cycles will not see them as distinct devices and won't be able to use both of them, which is a big downside even if SLI works (now or in the future) with Eevee.

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