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Old 05-21-11, 11:03 PM   #1
johnc
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Join Date: May 2011
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Question Switching between MultiGPU and TwinView

Hi,

I have a 7950 GX2 which has two GPUs and I'm running a TwinView configuration. I understand that one can't enable both the Multi-GPU feature and TwinView simultaneously.

However I'd like to modify my Doom3 launch script to automate switching between these two configurations. (E.g., disable twinview, enable multi-gpu, run doom3, then reverse the options after doom3 exits.)

If I understand correctly, changing TwinView or Multi-GPU requires an X restart (feeling queasy here) to reload the xorg.conf. Does anyone know a way to do this without logging out of a session? Doesn't the nvidia-settings GUI restart X when TwinView changes are applied (seems to require elevated privileges)?

Or... does anyone have a better way of doing this (switching between desktop / gaming configurations)?

Thanks for any advice.

-John

PS: For the 7950 GX2... the correct option to turn on would be MultiGPU -- not SLI -- right?
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Old 05-22-11, 03:44 AM   #2
MaDDeePee
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Default Re: Switching between MultiGPU and TwinView

What about a separate X for this?

(a second xserver layout)
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Old 05-23-11, 04:44 PM   #3
johnc
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Default Re: Switching between MultiGPU and TwinView

Quote:
Originally Posted by MaDDeePee View Post
What about a separate X for this?

(a second xserver layout)
Thank you for that great idea as it got me started in the right direction!

I was able to create a separate ServerLayout in the xorg.conf, then launch a second X session on another virtual terminal (using startx -- :2 -layout layoutname), and launch my beautiful Doom3 on that X, while my gnome session remained unamused on my initial VT. (BTW I'm surprised how little overhead there appears to be with the second X server running.)

The trouble began when I tried to enable multi-GPU support in the new ServerLayout. I tried putting the option in the "Screen" section and then the "Device" section, but whenever I switch between VTs (e.g., when I ended my second X session), my machine got totally borked. The displays were hosed and my keyboard wouldn't do jack. Only option was the reset button.

So then I decided to just get multi-GPU working on my primary layout configuration / VT / gnome session. The Xorg log file indicated that it was enabled, so I think it's working. The nvidia-settings GUI showed both GPUs associated with my X screen (but no options under GPU-1). And after a Doom3 session the temps on both GPUs appeared elevated.

However there was an insane amount of tearing or some kind of artifacts while playing Doom3 (and then, after I exited, in Compiz as well). So I'll have to do some more research on that.

tl;dr version -- multi-gpu is funky; I'm not sure that you can have it simultaneously enabled on one X and disabled on another.
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