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Old 02-06-05, 12:53 AM   #1
ChrisRay
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Join Date: Mar 2003
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Arrow NVIDIA SLI investigation

Introduction



Introduction: When Nvidia first announced SLI I was impressed by claimed performance increases. Naturally I was also a bit dubious. Hearing alot of information around the internet I have been reading both negative and positive opinions about the SLI setup. Naturally I have wanted to test an SLI setup myself to better formulate my own opinion. After formulating that opinion I also wanted to share my results with others. So Welcome to my SLI Investigation Thread.


Rendering Methods:There are a few key terms which you will want to know regarding the rendering methods available to an Nvidia SLI setup. The first is SFR. SFR stands for Split Frame Rendering . The method is pretty well described by its name. The other mode available is AFR. Alternatively known as Alternate Frame Rendering which is also pretty well defined by its name. In my experience I have found AFR to be the better of the two. However if one does not seem to be functioning properly I do reccomend trying the other. Nvidia also has specifically optimised AFR and SFR methods within its drivers. I do not reccomend modifying these if they already have a custom built rendering profile built by Nvidia. These can be seen and noted by there bizarre label in the profiles which we will cover shortly.


Profiles: At the very heart of Nvidia SLI lies Nvidia Profile system. Originally introduced last year during the Geforce FX era. Profiles allow the drivers to manually configure settings such as Anti Aliasing, Anisotropic Filtering and now SLI rendering modes. The Nvidia drivers detect the program .exe file and load up the proper settings. To protect users from rendering errors Nvidia has made the SLI profiles non switchable within the control panel. Power Users however may find multiple ways to enable SLI in any application they desire.

#1: SLI Profile Editor released at *********.com . This is my preferred method for editing SLI profiles. Its quick. It's fast and it allows easy entry of SLI profiles within the drivers.





#2: Manually Editing the nvapps.xml which can be found in the Windows\System folder. A Properly enabled SLI application will look something like this below. I dont reccomend employing this method if you are not at least familiar with markup language. I've illustrated a few examples to give users an idea of what to look for.

Code:
 <PROFILE Label="Nvidia Vulcan Demo">
			<APPLICATION Label="vulcan.exe"/>
			<PROPERTY Label="multichip_rendering_mode" Value="1" Itemtype="predefined"/>
			<PROPERTY Label="aa_default" Value="10000000"/>
#3: A new application has been released by Grestorm. This is tool is not just useful as an SLI profile enabler but an all around package for tweaking graphic settings and performance. It is easiest of the available methods for enabling SLI. Currently the drawback is that it requires Microsoft Net 1.1 Framework to be installed on your computer. You will be able to switch and change between various SLI profiles as well as enable some specific compatibility bits. It will lock out Nvidia specific assigned profiles by default and I dont reccomend editing these unless your absolutely sure you know what your doing. The application itself can be downloaded here. One final note. This is the only application currently available that lets you globally force SLI to be enabled in either AFR, SFR or Single which is excellent for certain applications which have trouble with profiles.




Selecting the Right Rendering Mode: As described above there are 2 rendering methods for enabling SLI. SFR: 2 And AFR: 1 . Please denote the numbers next to the two rendering modes. You will be using them to enable and switch between the various rendering modes. The SLI Profile Editor released at *********.com will allow you to choose between AFR and SFR when setting the profile. Clearly labeled by the number denotion in the application. You may also edit the NvApps.xml file with a proper profile as shown above. The last important thing to note. Number 4 disables SLI and forces you to use a single GPU to render.


Watch Out for Nvidia Specific Profiles: In the NvApps.xml there are specifically optimised AFR and SFR modes for certain applications. These can be seen because they have neither a 1, a 2, or even a 4, in them. An example shall be listed below. Altering these with a non optimised SLI profile will likely prove to be detrimental to your SLI performance.

Code:
 <PROFILE Label="Tomb Raider">
			<APPLICATION Label="TRAOD.exe"/>
			<APPLICATION Label="TRAOD_P3.exe"/>
			<APPLICATION Label="TRAOD_P4.exe"/>
			<PROPERTY Label="prevent_cpl_aa" Value="1" Itemtype="predefined"/>
			<PROPERTY Label="multichip_rendering_mode" Value="2C10401" Itemtype="predefined"/>
		</PROFILE>
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Nzone
SLI Forum Administrator

NVIDIA User Group Members receive free software and/or hardware from NVIDIA from time to time to facilitate the evaluation of NVIDIA products. However, the opinions expressed are solely those of the members

Last edited by ChrisRay; 02-19-05 at 07:53 PM.
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