Dual-GPU: which is the "display" one, and what does it mean?

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So I have this rig on Windows 10:

  • i7-5820K
  • GTX 1080
  • GTX 560 SE
  • 2x 1440p monitors
  • MSI x99A SLI Plus (no on-board graphics, and no, I’m not running those GPU in SLI, it’s just the mobo’s name)

I have a hard time understanding what’s the best way to work with dual GPUs in Cycles, especially for real-time previews, which can make the computer really sluggish when using a single GPU. Now clearly one of my GPUs outperforms the other. Both my monitors are plugged in my 1080. That brings me to my first question: does the fact that my monitors are plugged in my 1080 make my 1080 the “display” GPU? If so, why do the options I get in user preferences are those:


It’s written “display” after all of them. Is this normal?

Also, since my 1080 is much faster at rendering than my 560, it would be natural to set the 1080 as my rendering card and use the 560 for display. But I also use my computer for gaming, watching 1440p videos and other tasks that run better on my 1080. So if the card in which the monitor is plugged in determines what GPU is the “display” one, does that mean that I have to manually unplug and replug my monitors depending on what I’m doing? Could there be another way, for instance can whatever is displayed on the screen be rendered on a GPU and the output routed through the other via some obscure nVidia setting?

And what would happen if I were to plug one monitor in the 1080 and the other in the 560? Would game performance change if I play in windowed mode and drag the window in the other screen? Or would half of it be rendered on a GPU and the other half on the other? That doesn’t seem to be plausible. Basically it all comes down to the same question: what determines what is a “display” GPU? Is it a hardware-, OS-, or application-specific setting? How do these levels interact with one another when it comes to outputting frames on a monitor? I tried to search online but I haven’t found any conclusive answer.

Any help is much welcome, including other resources that explain this well, preferably not TOO technical.

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oh, please dont drag a windowed game between the two monitors! last time i tried that, it crashed the computer. :smiley: but in theory, the performance would change.

check your SLI, make sure its OFF in the nvidia panel. i dont know how smart that thing is.

unfortunately, yes, you would have to manually move the monitor(s). preferably while the computer is off, its just a bit safer.

i personally quit using two monitors, it got too messy. then again, im not a huge multitasker.

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does the fact that my monitors are plugged in my 1080 make my 1080 the “display” GPU?

Yes.
The display label on all cards is a bug, I don´t have this on Linux, but is not reported to bug tracker so far I know.
For Cycles it is best to take the slower card for display and disable it for render.
For gaming it is the other way around.
I would check one display connected to 560 and run Blender on it, no idea if this work.

Cheers, mib