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Re: Dual GPU dual display support in Debian?

Anssi Saari writes:


I was wondering, since I didn't really find anything definite via Google
but is dual GPU dual display actually a supported configuration in
Debian 11?


I would be interested in knowing about that, too.


So basically for a while I ran this kind of setup:

Display 1 connected to CPU's integrated GPU (Core i7-4790K, Intel HD
Graphics 4600).

Display 2 connected to Nvidia RTX3070Ti.

The two displays setup as a single wide display, i.e. windows
movable/draggable from one display to the other.

I have a triple boot setup, Windows 10 worked fine, Arch Linux with KDE
was hit or miss, Debian didn't work, no image on one display and xrandr
saw only one display. Which one seemed to depend on which GPU was set as
primary in the UEFI setup. No xorg.conf but I fiddled with that too.


[...]


The reason for this setup was that Debian 10 has no drivers for the
RTX3070Ti so I just used one display there and since it worked in Arch
(at least sometimes) I figured it should just start working in Debian 11
after the upgrade but it didn't.
I believe it might be easier to fix the problem by attaching all displays to the NVidia GPU. Here are some hints about what you might check to make the NVidia GPU work under Debian 11: 

https://forums.developer.nvidia.com/t/linux-460-driver-kubuntu-20-04-rtx-3070-not-booting/171085
About doing a "dual GPU dual display" my experience is as follows (from Debian 10 oldstable/buster with purely X11 and no Wayland): 

First, I never got it to work properly.
Closest I could get was to run two different window managers on the respective displays all under the same X server. This allowed the mouse and clipboard to move across the screens but the windows needed to remain on the GPU they were started on. Additionally, one cannot combine arbitrary window managers this way - I used i3 and IceWM. The trick is to not have them compete for "focus". The `.xsession` looked as follows: 

	DISPLAY=:0.1 icewm &
	exec i3
IIRC there were also some approaches like starting an X-server on top of the two X11 displays (:0.1 etc.) but I cannot seem to find them right now. Back when I tried that setup, it seemed these would be unable to provide graphics accelleration, hence I opted for the more convoluted variant with two window managers and full performance. 

HTH
Linux-Fan

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