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Old 07-22-10, 05:31 AM   #1
Ulukai
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Default Geforce GTX SLI under Linux

I'm thinking of getting a pair of GTX 470's to SLI under Linux, so I was reading some information and found this in the readme of the latest Linux driver. As it says, it would be only temporary, but I coudln't help noticing it's in the readme a very long time already: driver 180+ and even older.

Why is Doom 3 slower when SLI or Multi-GPU is enabled?


The NVIDIA Accelerated Linux Graphics Driver does not automatically detect the optimal SLI or Multi-GPU settings for games such as Doom 3 and Quake 4. To work around this issue, the environment variable __GL_DOOM3 can be set to tell OpenGL that Doom 3's optimal settings should be used. In Bash, this can be done in the same command that launches Doom 3 so the environment variable does not remain set for other OpenGL applications started in the same session:

% __GL_DOOM3=1 doom3

Doom 3's startup script can also be modified to set this environment variable:

#!/bin/sh
# Needed to make symlinks/shortcuts work.
# the binaries must run with correct working directory
cd "/usr/local/games/doom3/"
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:.
export __GL_DOOM3=1
exec ./doom.x86 "$@"

This environment variable is temporary and will be removed in the future.


So a couple of questions about this:

- Does it really still apply or did someone forget to remove it from the readme?
- To fix this for Quake 4 (and maybe Prey too?), do we have to use the same variable with the same name (__GL_DOOM3) or is it called different?
- When I enable SLI in xorg.conf, should I have 2 sections "device" for both cards?

Thanks for your help,

Ulukai.

Last edited by Ulukai; 07-26-10 at 02:06 AM.
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Old 07-26-10, 02:07 AM   #2
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Default Re: Geforce GTX SLI under Linux

Nobody with SLI enabled who can answer the xorg.conf part?
Maybe a Nvidia dev can help me out with the Doom 3 part?

Thanks for your help.
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Old 07-26-10, 10:11 AM   #3
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Default Re: Geforce GTX SLI under Linux

SLI with GTX 480 performs horrible in Linux, I brought this issue up a month ago in another one of my posts. I'm sure it'll be exactly the same with 470's.

The performance is so stuttering that its much slower than just a single card. Forget the GL_DOOM3 hack, this is a much larger problem. Ungine Heaven runs like crap too with SLI enabled, its like a slideshow.

Single card everything is fine however. NVIDIA really needs to test and develop on SLI more. Right now it seems they're not doing much to make sure that part of the drivers are actually working properly with new cards.
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Old 07-27-10, 01:53 AM   #4
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Default Re: Geforce GTX SLI under Linux

Really? Damn, that's a bummer. I already ordered an SLI motherboard to replace my Crossfire motherboard.

I assume you are running the latest drivers 256.35? As far as I know, Linux shares 95% of their Nvidia drivers with Windows, shouldn't the performance be comparative? What did the devs have to say about this in your thread?

How did you enable SLI? Which xorg option did you use and can you paste your xorg here?
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Old 07-27-10, 09:35 AM   #5
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Default Re: Geforce GTX SLI under Linux

Quote:
Originally Posted by Ulukai View Post
Really? Damn, that's a bummer. I already ordered an SLI motherboard to replace my Crossfire motherboard.

I assume you are running the latest drivers 256.35? As far as I know, Linux shares 95% of their Nvidia drivers with Windows, shouldn't the performance be comparative? What did the devs have to say about this in your thread?

How did you enable SLI? Which xorg option did you use and can you paste your xorg here?
Without application profile support SLi (or crossfire for that matter) in linux is largely useless. We see the same thing happen in windows when a game gets released and where the drivers don't have a profile for that game yet.
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Old 07-27-10, 11:37 AM   #6
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Default Re: Geforce GTX SLI under Linux

This problem goes beyond SLI profiles. Every game I try, and Heaven, stutters like mad.
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Old 07-28-10, 02:01 AM   #7
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Default Re: Geforce GTX SLI under Linux

The profiles, don't they just tell the driver to use SLI AFR or SFR? Have you tried both options in xorg or always used auto-mode?

Will we ever get an interface to create profiles, like it is done for Windows? It can't be that hard to include it in nvidia-settings. Also there should be more SLI configuration options, like enabling or disabling and choosing the rendering mode in the GUI.

So for the record, does the driver include some profiles, or none at all? Is the driver always guessing for the right rendering method?
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Old 07-28-10, 11:08 AM   #8
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Default Re: Geforce GTX SLI under Linux

Profiles are not just limited to AFR / SFR. There are other optimizations done on each specific game title.
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Old 07-28-10, 11:20 AM   #9
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Default Re: Geforce GTX SLI under Linux

Another thing to note is that many many many games in linux simply do not push the graphics card hard enough for sli to make any appreciable difference. Most of the games out there for linux are CPU limited so SLi makes very difference unles extreme overclocking to the CPU is done or resolution is cranked up to insane resolutions. With increasing the resolution however you may quickly run out of memory on the card. Trying to run Unigine's Sanctuary for example on a couple of 8800GT's with 512 Megs in sli @ 1920x1200 will quickly gobble up the available texture memory and studder like hell. This issue has been known for a long time by Unigine's developers (well over a year and a half now). When running the benchmark in DX mode it does not run out of texture memory and runs smooth. The same running out of texture memory issue occurs as well in Windows when running in oGL mode.
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Old 07-28-10, 02:56 PM   #10
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Default Re: Geforce GTX SLI under Linux

Quote:
Originally Posted by Deanjo View Post
Another thing to note is that many many many games in linux simply do not push the graphics card hard enough for sli to make any appreciable difference.
Maybe a bit away from the topic but would SLI for games in wine make sense or work at all ? I have one GTX470 and will maybe get another one some time but my pc is linux only so i wonder if its worth yet.
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Old 07-28-10, 03:33 PM   #11
Ulukai
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Default Re: Geforce GTX SLI under Linux

When Primal Carnage is released and Doom 4 or Rage will be hitting Linux, GTX 470 x 2 will be interesting to play smoothly no matter which CPU you are using at that moment.

But the question remains: how well does SLI witht he latest Fermi cards do on Linux? Any other users experience the same problem as Spyke? Will Nvidia improve the GUI and profiles?

Also, does anyone know about the Doom 3 hacks above?
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Old 07-28-10, 03:35 PM   #12
Ulukai
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Default Re: Geforce GTX SLI under Linux

Quote:
Originally Posted by Milena View Post
Maybe a bit away from the topic but would SLI for games in wine make sense or work at all ? I have one GTX470 and will maybe get another one some time but my pc is linux only so i wonder if its worth yet.
Found this in the forum archives (2007):

As of Nvidia Driver 100.14.11 and my SLI setup in AFR. WoW runs awesome, 70-130 fps in the Outland or Azeroth. I still have serous FPS drops(25-35) in some towns and large citys. When indoors or in the Under City I average about 90-130fps. In Arctic Valley BG I get 35-85 and spikes to 130 depending on how many players are on screen. Its not the silver bullet but it makes the Battlegrounds a whole lot more playable.

Also Byteframe, booting Linux with vga=normal fixed a whole set of problems for my 8800gtx the same should hold true for your 8800gts.
Extreme Coder
07-04-2007, 07:50 PM
So is the game faster than without SLI?
Throwing Strikes
07-08-2007, 12:34 PM
Its faster with SLI!!!
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