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-   -   Nvidia 6800GT SLI investigation (http://www.nvnews.net/vbulletin/showthread.php?t=47710)

ChrisRay 03-16-05 05:50 AM

Nvidia 6800GT SLI investigation


A Month and half ago I decided I wanted to dabble in the SLI front from Nvidia. I had read alot of things and decided I wanted to give it a try. My initial impressions were posted in this thread where I discussed the pros and cons of SLI. Things have come along way since then and profiles could never be easier to setup. If you're not satisfied with setting up profiles you are now also able to globally force SLI in the control panel providing you have the Coolbits Tweak installed on your system.

Step 1: Downloading and Installing coolbits. Coolbits can be downloaded several places but you can get here as well. After downloading coolbits2.reg you'll want to right click the file and merge it into your registry.

Step 2: At this point all you have to do is enter your control panel and globally force SLI in either Split Frame Rendering, Alternative Frame Rendering, or Single GPU Rendering. You can access these modes by selecting the "Show Advanced Settings" in the control panel.


Step 3: Setting up your SLI Profile within the drivers. The advantage of setting an SLI profile is that when you find your desired SLI rendering mode you are able to save it and the Nvidia drivers will forever pick up on it and automatically overwrite any global driver settings you have. This is exceedingly useful and convenient when dealing with SLI making it a one time setup for individual games that do not support SLI by default


Step 4: Play on! Once you have your SLI rendering method setup in either a global driver setting or SLI profile you will be able to play games with SLI enabled. Quite an improvement since my last article showing that Nvidia has been taking the steps to make SLI easier to use for everyone. One thing to note is if the SLI profile is already activated by default you cant change it within the control panel. I still advise editing the nvapps.xml and removing the "predefined" tag for SLI profiles that Nvidia has set and you wish to change manually. The other option is to use Nhancer which will also allow you to manipulate predefined SLI settings.

Tip 1: If Nvidia has a custom SLI profile for a certain app. Its probably best to leave it alone. Many SLI apps specified by Nvidia have specific compatibility bits which either improve performance or compatibility

Tip 2: Check out the load balancer in the SLI panel of the Nvidia Drivers. It will allow you to see how each game is being loaded on each GPU

Tip 3: If SLI doesnt not seem to be helping your performance. Try turning up the graphic resolution or anti aliasing settings. In many cases you are CPU limited and you can get away with quality settings for free with SLI.

ChrisRay 03-16-05 05:50 AM

Re: Nvidia 6800GT SLI investigation

Test Setup

Athlon 64 3800+ @ 2.4 Ghz
Asus A8N SLI Deluxe
Geforce 6800GT x2 SLI
1 Gig DDR400 (Dual Channel)
71.84 Drivers



3dmark2k1 isnt terribly useful as a benchmark these days for graphic card referencing. All but 1 game test is completely CPU limited on modern graphic cards. However there are a few decent tests which scale well with graphic cards. The first important thing I would note is the Advanced Pixel shader test which makes use of pixel shader 1.4. The Geforce 6 series and SLI do exceedingly well in Pixel shader 1.4. It is also interesting to see how 2 6800GTS exceed 10000+ Fillrate in AFR mode. Quite a feat for modern graphic cards and certainly not something I expected last year!

Profile: Nvidia Custom AFR


Despite the controversary surrounding 3dmark03 on it's release it has still proven to be a popular test. My personal opinion is that Game Test 2 is the most reflective game as it uses similar rendering techniques seen in Doom 3. With the exception of Game Test 1 which is partially CPU limited all tests scale extremely well giving us a hint of how SLI will react to GPU/pixel bound scenerios.

Profile: Nvidia Custom AFR


3dmark05 is Futuremarks latest installment of the legendary 3dmark series. Once again you can see the test is purely bound by the graphic subsystem and unlike 3dmark03 there are no tests which show any real strong CPU reliance. SLI scales accordingly reaching an amazing score of 9000+.

Profile: Nvidia Custom AFR


Aquamark was one of our first alternative DirectX 9.0 benchmarks to 3dmark03 when it was released. This was actually a test that somewhat disapointed me. While i SLI didnt scale as well in this test it still was able to bring the score up by a significant margin. The test increases FPS by about 10 overall. Which is a fairly impressive leap for Aquamark.

Profile: AFR


I wanted to take a closer look at shader performance in AFR mode and Rightmark seemed to be the perfect program to do it. This fully customizable application allows you to test various shader functions with your graphic accelerator. I decided to focus on pixel performance because that is where current games are headed. Most notable is the very strong showing the SLI setup shows with pixel shader 1.4 model. The test nearly reaching 1000 FPS! The pixel shader 2.0 tests also scale exceedingly well. All tests were configured @ 1024x768 @ 100 Hz.

Profile: AFR


As with my prior SLI Article I wanted to test to see if SLI would show any real world benefits to shader limited scenerios beyond benchmarks. Obviously the results speak for themselves. The Ati demos ironically seem to scale better than the Nvidia demos. Another interesting note is how the Nalu demo did not seem to want to exceed 24 FPS. Perhaps a CPU limitation or something else.? I am not too sure. I will have to investigate further.

Profile: AFR

ChrisRay 03-16-05 05:51 AM

Re: Nvidia 6800GT SLI investigation


Benching Methodology: All benchmarks were done with fraps. I took 3 preset runs through a specific area of each map and divided the results by 3 to take the average. Average results were usually within 1 FPS. I feel these real time results are more accurate than time demos because they take into account in all game factors.


Half Life 2 was to be this years poster child DirectX 9.0 game. The game features a plethora of DirectX 9.0 shaders running in full FP32 precision on Nvidia hardware. Despite all this there are many situations where Half Life 2 appears to be CPU limited. Under many circumstances I found the minimum frame rate to be rather constant in this map. Otherwise SLI does seem to be doing its job. In Situations where 8xAA is used you see almost double performance.

Nvidia Custom AFR profile


As Half Life 2 is the poster child DirectX engine. Doom 3 is the poster child OpenGL engine for this last year. Most notably is the graphic engine seems to be completely limited by your graphic setup at these resolutions and scales accordingly. The game was completely playable @ 4xAA/16xAF with 1600x1200 resolution. To me this is quite a feat because even on a single 6800GT I have had to settle for less than that due to the game becoming choppy occasionally. The 8xAA solutions werent really playable with SLI with the exception of 1280x1024 resolution. However one thing really stands out. SLI is the way Doom 3 is meant to be played.

Profile: Standard AFR Profile


Far Cry was one of the first real tangible DirectX 9.0 games released. Offering stunning lighting and visuals and impressive wide open areas. The graphics were known for bringing last year and this years hardware to its knees. SLI scales fairly well with Far Cry. In most cases providing a pretty tangible increase. I was able to play Far Cry perfectly acceptably @ 1600x1200 with 4xAA/16xAF with no slow down. However 8xAA did not scale as well as we have seen in the prior games. This is probably due to the fact that the game uses SFR for its multi gpu rendering method. SFR usually does not scale as well as AFR unfortunately.

Profile: Nvidia Custom SFR Profile


Call of Duty is one of our tests that is not originally enabled for SLI by default. I had to coax it and edit out the single GPU rendering profile within the nvapps.xml. Then I enabled AFR through the control panel. This game is strongly CPU limited on an SLI setup. Even CPU limited @ 4xAA/16xAF at 1600x1200 resolution.. However turning up 8xAA/16xAF really allowed the SLI setup to stretch its legs. Call of Duty played at 8xAA/16xAF @ 1600x1200 resolution with smooth frame rates really is a site to behold.

Profile: Forced AFR profile


Admittedly this was my first chance to play Halo when doing this review. The game seems to feature a great deal of pixel shader 2.0 effects for speculiar effects among other things. The game does not seem to support anti aliasing so I left them disabled during this benchmark. In its stead I decided to use HQ anisotropic filtering for maximum quality in game. SLI once again scaled extremely well and brought many modes that were unplayable with a single GPU to a completely playable and enjoyable experience.

Profile: Nvidia Custom AFR Profile


I designed the Neverwinter Nights Harrowdale module. Back in the Geforce 4 days this game was very demanding on graphic cards and cpus alike.. I created the demo to use high amounts of fog and water effects rendered with pixel shaders. However like many other engines as time has passed its become an extremely CPU limited game that has not scaled well at all.. I know you're probably thinking. "Why bother benching this game?". The answer is pretty simple. If you have an SLI setup and are finding yourself CPU limited. You might as well crank it up.

Profile: Forced SFR Profile


Unfortunately this game didnt seem to scale well with SLI at all. Much to my surprise SLI provided minimal benefit to 8xAA. This could be seen by the fact that when you turned on 8xAA the load balancer fell to the bottom of the screen which means the secondary graphic card was doing very little. This didnt happen with the 4xAA tests. I speculate that 8xAA has become completely bandwith limited and SLI doesnt seem to scale as well with bandwith limited situations compared to situations which are fillrate limited. I have also noticed this oddity in Unreal Tournament games.

Profile: Custom SFR Profile

Conclusion: Well What can be said? SLI has come along way since I did my original article and that was only a month and a half ago! With Coolbits 2.0 you are able to manually set your own profiles within the Nvidia control panel as well globally force SLI. These are all steps in the right directions from the time I made my previous article.

What else can be said? Two Geforce 6800GTS operating in SLI mode provide ample performance with some to spare. I am happily going to be gaming on this rig for sometime to come. There are a few odd circumstances where SLI can fail such as games utilizing render to texture effects such as motion blur or bandwith limited games which are not limited by the GPUS graphic engine. However those issues aside. SLI has scaled exceedingly well and IMO there is no current better Dream Machine than a high end Nvidia SLI rig.

MUYA 03-16-05 05:55 AM

Re: Nvidia 6800GT SLI investigation
Thanks. I just like the fact that half the games show improved min FPS with SLI! (except Half Life2 can it be more cpu limited?)!

You should really buy Chronicles! :D

ChrisRay 03-16-05 06:00 AM

Re: Nvidia 6800GT SLI investigation
Now its time to edit out grammatical errors and my complete butchering of the english language heh

Rollo 03-16-05 06:51 AM

Re: Nvidia 6800GT SLI investigation
Nice article Chris- very well done!

SH64 03-16-05 07:21 AM

Re: Nvidia 6800GT SLI investigation
WOW that was quick :p
pretty good article Chris ! :D

So .. was HL2 smooth @1600x1200,8xAA,16xAF from a gameplay prespective in SP mode ??

ChrisRay 03-16-05 07:22 AM

Re: Nvidia 6800GT SLI investigation

Originally Posted by SH64
WOW that was quick :p
pretty good article Chris ! :D

So .. was HL2 smooth @1600x1200,8xAA,16xAF from a gameplay prespective ?? & how come your min fps never goes below 45fps ??

The point where I started my benchmarking always was 45 FPS. In SLI mode and in normal mode it was 45 as well in some places. This is probably because this paticular spot was CPU limited except on the single GPUs in 8x mode.. You can see how its CPU limited as well if you take note of the 6800GT @ 1280x1024 where the min is 48. Thus CPU overhead of SLI probably consistently dropped the minimum framerate)) Heh I felt the areas I played were Smooth, ((beginning, DM_Canals 1-3, and 5-6)) but I admittedly did not play the entire game.

SH64 03-16-05 07:24 AM

Re: Nvidia 6800GT SLI investigation

Originally Posted by ChrisRay
The point where I started my benchmarking always was 45 FPS. In SLI mode and in normal mode it was 45 as well in some places. This is probably because this paticular spot was CPU limited. Heh I felt the areas I played were Smooth, ((beginning, DM_Canals 1-3, and 5-6)) but I admittedly did not play the entire game.

oh i see , because i was wondering how the game plays @1600x1200,8xAA,16xAF in SP mode .

i would try it but i have problem logging on/off to play the game in my SLI pc :(

ChrisRay 03-16-05 07:27 AM

Re: Nvidia 6800GT SLI investigation

Originally Posted by SH64
I just noticed a DM demo .. i was wondering about the SP performance ??

It wasnt a demo. It was a loaded map. In your console for Half life 2, Type "map dm_canals6" and it will load you to the spot I did the benchmarking.((Well the outside part where all the water is and the broken boats) These werent done with demos. They were done in real time with fraps.

Btw. I included my benchmark methodology into the games section. So it would be more clear how I did it. I was kinda in a rush to get this in this morning so I missed alot of things and made many errors.

PSYCHODAD 03-16-05 11:01 AM

Re: Nvidia 6800GT SLI investigation
Hmm....gonna have to try out Call Of Duty @8xAA/16xAF @ 1600x1200 resolution :thumbsup:

Clay 03-16-05 08:10 PM

Re: Nvidia 6800GT SLI investigation
Very nice work as usual Chris. Sometimes I think we're spoiled here by the quality and thoroughness of your investigations.

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