I've just installed CentOS 6.2 on an HP xw8600 with two NVidia GeForce 8800
GT video cards in it. I have two Dell monitors than ran configured as a single
contiguous desktop when this was a Windows 7 machine. I've only been able
to access one of the two monitors under CentOS, although the system demonstrates
some awareness of the second GPU/monitor, because the second monitor shows the
standard CentOS 6 image while the machine is running. In addition, when
it's starting up or shutting down a large wait cursor is displayed in that
second monitor, and also shows the message "shutting down..." when
that's going on. However, the Display applet in the System | Preferences
panel menu shows only the one monitor, and hitting the Detect Monitors button
doesn't help. Just to test the obvious, I switched the DVI cables coming
out of the two video cards and as you'd expect what shows in the two
monitors is also switched.
When I do an lspci at the command line I see at the bottom of the listing:
60:00.0 VGA compatible controller: nVidia Corporation G92 [GeForce 8800 GT] (rev
a2)
80:00.0 VGA compatible controller: nVidia Corporation G92 [GeForce 8800 GT] (rev
a2)
And the output from xrandr is:
Screen 0: minimum 320 x 200, current 2560 x 1600, maximum 8192 x 8192
DVI-I-3 connected 2560x1600+0+0 (normal left inverted right x axis y axis) 646mm
x 406mm
2560x1600 59.9*
1280x800 59.9
DVI-I-4 disconnected (normal left inverted right x axis y axis)
I've done some considerable googling, and haven't found any discussions
that offer a solution for my situation (dual video cards). I did see the
following from almost two years ago saying X Windows just doesn't support
it:
>From http://permalink.gmane.org/gmane.comp.freedesktop.libdlo/448, Bernie
Thompson says (on October 13, 2010):
<begin quote>
On Wed, Oct 13, 2010 at 1:44 AM, Christoph Rissner <c.r at
...<http://gmane.org/get-address.php?address=c.r%2dxV8MHogwf5Dk7%2b2FdBfRIA%40public.gmane.org>>
wrote:
> I think I've read somewhere that even XRandR 1.3 isn't up to multi
GPU
> environments, so I guess Xinerama is the only option here.
Yes, unfortunately that's the fundamental problem.
http://superuser.com/questions/139818/ubuntu-10-04-not-detecting-multiple-monitors
I really only understand the low-level stuff (framebuffer driver), but
here's my understanding ...
The plumbing isn't there in X to support multiple graphics cards the
way Windows has since Win 98.
The main low-level features xorg needs are in the area of things like
"GPU object" and "shatter" support to allow screens to be
split across
GPUs/framebuffers.
Right now, with RandR hand-config, you can get multiple X screens
[can't drag windows between them], one per-GPU, each of which can have
multiple monitors connected if that particular GPU reports multiple
outputs. With GPU object support, rendering could span GPUs and
several GPUs could be merged into one X screen similar to the
classical Xinerama setup.
<end quote>
So is this [still] the case? Is Xinerama a viable alternative? I'd also
appreciate some help with the "RandR hand-config" that Bernie
mentions. Thanks for any info you may be able to provide.
-Steve Chall
Senior Research Software Developer
Renaissance Computing Institute (RENCI)
Phone: 919-681-9639
Email: stevec at renci.org<mailto:stevec at renci.org>