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Old 05-14-07, 10:12 AM   #1
aboteler
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Default Does anybody have SLI working on a GeForce 8800 GTX with Linux?

I have a workstation with two GeForce 8800 GTX in SLI configuration. However, when I enabled SLI mode through nvidia-xconfig my benchmark of the rendering time does not change, which leads me to believe the initial support they mention in the 1.0.9755 driver is just an API no implementation for SLI.

Is this true? Does anybody have SLI working?

Thanks,

Aaron
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Old 05-14-07, 11:01 AM   #2
ssross
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Default Re: Does anybody have SLI working on a GeForce 8800 GTX with Linux?

It works for me but the results are mixed. Some programs are a faster (but not much), most seem to stay about the same, and a few get slightly slower.

One thing that I noticed is that in the Auto mode you can get momentary stalls while it decides what to do. I noticed it mostly when moving windows in Beryl while the SLI hud was up It looks like it switches modes when you grab the window and there would be a pause (.2 - .5 sec) before the window would start moving. I didn't try to figure out if this was beryl's problem or the sli since I don't normally use beryl anyway.

One mode that works for me is the -sli=AA mode. If I set the mode to AA and the __GL_FSAA_MODE=12, I get sharp images with nearly no crawl - better than the 16Q - and without appreciable performance loss at 1920x1200.

Mostly I just leave SLI off right now since the card runs cooler and I don't have anything that works well enough to enable it. Looking at CUDA next, that might be a more interesting use for the second card anyway.

enjoy
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Old 05-14-07, 11:29 AM   #3
netllama
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Default Re: Does anybody have SLI working on a GeForce 8800 GTX with Linux?

aboteler,
Which benchmark are you running?
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Old 05-14-07, 01:29 PM   #4
aboteler
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Default Re: Does anybody have SLI working on a GeForce 8800 GTX with Linux?

This is an internally developed plume rendering app. I turned SLI=auto and saw no improvement and infrequently the system hung-up so I turned it off. I wanted to divide the processing load to reduce our total rendering time. Since I saw no change I decided to ask if SLI was actually implemented.

Thanks,

Aaron
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Old 05-14-07, 01:41 PM   #5
netllama
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Default Re: Does anybody have SLI working on a GeForce 8800 GTX with Linux?

SLI is implemented. If you'd like further assistance you'll need to provide this app along with an nvidia-bug-report.log.
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Old 05-15-07, 09:02 AM   #6
aboteler
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Default Re: Does anybody have SLI working on a GeForce 8800 GTX with Linux?

Thanks for the information. What cases is the SLI optimized for? What I assumed was using split frame rendering the geometry and pixel processing where divided between the two GPUs. Is there a GPU load tool available to measure the load on each GPU during a rendering run?

I am going to work on a stripped down app that I can submit for review.

Thanks,

Aaron
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Old 05-15-07, 10:20 AM   #7
AaronP
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Default Re: Does anybody have SLI working on a GeForce 8800 GTX with Linux?

SLI on GeForces works best with fullscreen games. You didn't describe your benchmark app, but if it runs windowed, then I wouldn't expect to see much SLI scaling unless you're using a Quadro.
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Old 05-15-07, 10:20 AM   #8
netllama
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Default Re: Does anybody have SLI working on a GeForce 8800 GTX with Linux?

If you activate the heads-up display in nvidia-settings you'll see how the load is split across the GPUs.
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Old 05-15-07, 02:22 PM   #9
aboteler
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Default Re: Does anybody have SLI working on a GeForce 8800 GTX with Linux?

I forgot to mention I am using offscreen framebuffers. Is SLI applicable to offscreen framebuffers? Also when you say windowed I assume a window on the desktop therefore the onscreen framebuffer is used.

Is a quadro required to have SLI enabled for offscreen framebuffer rendering?

Thanks,

Aaron
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Old 05-15-07, 08:44 PM   #10
AaronP
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Default Re: Does anybody have SLI working on a GeForce 8800 GTX with Linux?

Currently, SLI doesn't apply to offscreen rendering.
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Old 05-16-07, 07:44 AM   #11
aboteler
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Default Re: Does anybody have SLI working on a GeForce 8800 GTX with Linux?

Will SLI support offscreen framebuffer rendering with unclamp float color values in the future?

Thanks,

Aaron
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