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Old 04-29-07, 12:02 AM   #1
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Join Date: Apr 2007
Posts: 3
Default Multi GPU setup not being utilized properly

G'day peoples!

I've currently scored myself a Leadtek 7950 GX2 to play with, but i'm having issues with getting the dual GPU'ed'ness to give different results compared with a multi-screen/single GPU config.

My gentoo system is as follows:

Linux tiptop 2.6.20-ck1 #14 SMP PREEMPT Wed Apr 25 21:07:40 CST 2007 x86_64 AMD Athlon(tm) 64 X2 Dual Core Processor 4600+ AuthenticAMD GNU/Linux

LInux nvidia drivers version 97.55

Im convinced the multi-gpu setup is begin recognized, as the nvidia-settings gui states that GPU 0 and GPU 1 are listed as GPU's of X Screen 0. Also not to mention that Xorg.0.log contains the following.

(**) NVIDIA(0): NVIDIA Multi GPU auto-select rendering option.
(II) NVIDIA(0): NVIDIA Multi GPU enabled.

I haven't a lot of test apps, but I have tested glxgears and doom3.

glxgears was running at full screen (~1792x1344) and at varying AA levels (0x -> 16x). Frame rate results were identical with mutli-gpu and multi-screen configs.

One interesting result which i think propogates onto doom3 also, is that defining "MultiGPU" as "AA" or "SFR" has adverse effects on frame rates; actually lowers it! So something odd is going on here, but im not sure what.

As for doom3, i have some basic benchmark results comparing average frame rates on windows XP (multi-gpu and non-multi-gpu configs) and Linux. I realize these aren't really nessesary to make a conclusion on my findings, but never the less i'll post them.

All results were obtained with AA 4x and AF 8x on timedemo demo1.demo

Windows - multi-gpu

1024 x 768 - 142 fps
1600 x 1200 - 105 fps

Windows - non-multi-gpu

1024 x 768 - 109 fps
1600 x 1200 - 57 fps

Linux - both multi-gpu and non-multi-gpu

1024 x 768 - 88 fps
1600 x 1200 - 54 fps

Linux doom3 was executed with the command $ __GL_DOOM3=1 doom3

I recognize that linux drivers are still immature compared to windows drivers hence the difference between windows non-multi-gpu and linux.

ive attached my xorg.conf and nvidia-bug-report.log as well as my kernel config if that is useful to anyone.

If anyone has a clue to why multi-gpu mode doesn't seem to give any differing results, i'd love to hear it!

I have tried the 100.xx nvidia drivers but cannot get it to run. See http://www.nvnews.net/vbulletin/showthread.php?t=90572

Attached Files
File Type: bz2 nvidia-bug-report.log.bz2 (26.7 KB, 107 views)
File Type: bz2 xorg.conf.bz2 (1.0 KB, 112 views)
File Type: bz2 .config.bz2 (7.5 KB, 101 views)
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Old 04-29-07, 03:01 AM   #2
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Posts: 2,487
Default Re: Multi GPU setup not being utilized properly

According to your log, your desktop is 1792 x 1344. Please try using xrandr to resize your desktop to 1600 x 1200 and 1024 x 768 before running the Doom 3 timedemo.
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Old 04-29-07, 05:07 AM   #3
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Default Re: Multi GPU setup not being utilized properly

Gday AaronP

Believe it or not i just stumbled across a source here http://www.phoronix.com/scan.php?pag...item=338&num=1 which re-iterates what you have said.

I've spent the best parts of 2-3 days trying to find the cause!

I now get 85 fps @ 1600x1200 and 103 fps @ 1024x765. Although im glad to now have it running, this is quite a different story to the XP frame rates. Is it just a matter of time before these drivers catch up to their windows counter part?

Also, what's the deal when you are running windowed opengl apps? I'm currently doing my own opengl programming where i can switch it from windowed mode to a "fullscreen" mode (fullscreen reallly just means hiding of window styles and other desktop gear). Will I automatically get SLI rendering when the gl viewport = desktop size, or is there something more fundament that i need to know?

Thanks again!
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