Gnome 3 - Multiple Video Cards - Xinerama -- Forced Fallback Mode

Question

Just installed a 2nd nvidia video card -- previously had gnome 3 working perfectly with 2 monitors on a a single video card using twinview

tried a number of things thus far

• twinview on 1 card + xinerama
• no xinerama no twinview
• various manual xorg.conf hacks based on random forums (couple references below)
• xinerama no twinview with and without Extensions Composite

The last one is what I'm using now -- it results in a forced fallback mode with Composite Disable set at the end of xorg.conf via nvidia-settings

Section "Extensions"
    Option         "Composite" "Disable"
EndSection

when I disabled that last snippet it boots to gnome 3 full with the left monitor on a black screen and the middle monitor as primary but non-responsive switching to console mode Ctrl+Alt+F1 and then switching back I get 3 black screens with a mouse that can move around but nothing to interact with

issue seems related to OpenGL and the multiple video cards -- I can boot into Unity without issue though my Glx-Dock shows up with the black background as barely shows in the screenshot below indicating the OpenGL is not initiated

has anyone had any luck with getting Xinerama to work with Multiple NVidia Video Cards with OpenGL support?

Found this in the logs while looking a bit further

[    23.208] (II) NVIDIA(1): Setting mode "nvidia-auto-select+0+0"
[    23.254] (WW) NVIDIA(1): The GPU driving screen 1 is incompatible with the rest of the
[    23.254] (WW) NVIDIA(1):     GPUs composing the desktop.  OpenGL rendering will be
[    23.254] (WW) NVIDIA(1):     disabled on screen 1.
[    23.277] (==) NVIDIA(1): Disabling shared memory pixmaps
[    23.277] (==) NVIDIA(1): Backing store disabled
[    23.277] (==) NVIDIA(1): Silken mouse enabled
[    23.277] (==) NVIDIA(1): DPMS enabled

According to this page at the NVidia User Docs

• http://us.download.nvidia.com/XFree86/Linux-x86/173.14.09/README/chapter-14.html

I may be out of luck =(

---

Starting this question with the hopes that others may be able to help debug and perhaps gain answers over time as I really want to get the full gnome 3 back.

Solution

The issue from what I could make out was with Xorg itself. X.Org does NOT support composite extension when xinerama is enabled. And all the new desktops like Unity,Gnome Shell etc. REQUIRE composite to work in the "full" feature mode. In my dual-monitor setup I could just use twinview and everything is fine with Unity and Gnome Shell since composite extension works with twinview. However for anyone have 3+ monitors who NEEDS to use xinerama , I strongly reccomend using XFCE under xubuntu-desktop . XFCE has solid xinerama support and can work just fine without composite extension. Also , it supports something out of the box I haven't found in any other "new" shell - the ability to set wallpapers "per" monitor.

Comments

[Jorge M. Treviño]

Alvin, I've read somewhere that Nvidia has made plain they don't care about Linux. My experience with their cards has always been spotty, to the point that in my desktop workstation for photography I pulled out an Nvidia video card that was causing me crashes (took me three months to pinpoint the culprit) and downgraded to an ATI Radeon HD that has been absolute solid since then. Pity I can't do the same to my laptop. Twin monitors are a PITA with it. Can't help beyond that. Many thanks for the 3D72D suggestion with my PS headache.

[Weich92]

Hey Jorge -- I had that experience in years past with gnome 3 I had an ATI card (have 2 in closet) and found that there is atleast 1 leak between the proprietary drivers and gnome that left my my processor using almost a full core (90-98%) to run gnome-shell -- I've found the interface valuable in terms of productivity having adjusted and tweaked -- currently running unity 2d without any trouble -- there seems to be an issue with the opengl and xinerama though I haven't had time to dig in much further since writing this post

[keepitsimpleengineer]

I use two monitors with two nvidia graphics adapters. However the nvidia cards are run with SLI and the monitors are separate X screen. This ran successfully in 10.04 and 10.10, but the second screen has caused problems with 11.10 and 12.04 with gnome classic, specifically causing the multiple upper and lower panels shown in your screenshot⋯as well as other things. This bug bugs.launchpad.net/ubuntu/+source/compiz/+bug/1002641 and related bugs.

[Weich92]

Yeah SLI isn't gonna work on this rig as they are 2 different model cards (though I had a Nvidia tech confirm they are both 8+ series so that scratches the idea of replacing one card) -- started a thread on nvidia forums at nvnews.net/vbulletin/…