NVIDIA's GeForce 6 SLI: Demolishing Performance Barriers
by Anand Lal Shimpi on November 23, 2004 10:23 AM EST- Posted in
- GPUs
Half Life 2 Performance
Given our recent focus on Half Life 2 performance, it should be no surprise that we start off our performance coverage with Valve’s latest title. The benchmarks we used for this review were created in house and are all documented (as well as available for download) in Parts 1 and 2 of our Half Life 2 GPU Roundups. One word of caution however, the benchmarks in those reviews used NVIDIA’s 67.02 drivers, however those drivers in particular do not yet have SLI support, thus we were forced to use older 66.93 drivers for this review – thus making our NVIDIA Half Life 2 numbers not directly comparable between these reviews.
Half Life 2: AT_canals_08
In this first demo we notice a couple of things; for starters, there is a small but consistent performance drop when enabling SLI. The reason behind this performance drop is because at lower resolutions we are still CPU limited with the higher end 6800 based GPUs, thus the additional overhead of splitting up the rendering and forwarding data from one GPU to the next for recombination ends up making SLI slightly slower than just a single GPU. That being said, no one would realistically have $800+ worth of video cards and run at 1024 x 768.
Looking at 1280 x 1024 there begins to be more of a performance benefit to SLI, but the benefits are not really significant until we hit 1600 x 1200. At 1600 x 1200 the 6800GT and Ultra are still somewhat CPU limited, but the 6600GT is far from it. Moving to two 6600GTs increases performance by 67% and delivers higher performance than a single 6800 Ultra, 9.5% faster to be exact. This scenario alone showcases the upgrade potential for SLI; purchasing a single 6600GT today allows you to run Half Life 2 at 1024 x 768 quite well, but adding a second card later on will let you run at higher resolutions (or more GPU intensive games). Assuming you can add that second card later on for less than you purchased the first one, your upgrade path actually puts you in a better situation overall than had you just purchased a single, more expensive card at the start. Keep an eye on this comparison between two 6600GTs and a single 6800GT/Ultra to evaluate the mainstream upgrade path benefits of SLI.
With 4X AA and 8X AF enabled, the situation changes dramatically. Although the performance gains are impressive, the pair of 6600GTs isn’t able to outperform a single 6800GT/Ultra. For 6800GT/Ultra owners, SLI enables smooth playability at high resolutions with AA and AF enabled. We play tested much of Half Life 2 with two 6800GTs at high resolutions with AA/AF enabled and for the most part the game was butter smooth; at 1600 x 1200 with 4X AA/8X AF enabled however there were some areas where even two 6800 Ultras would get choppy. But most resolutions and settings that were not smooth before on a single card were definitely playable thanks to SLI.
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bob661 - Tuesday, November 23, 2004 - link
I find it absolutely amazing that they were CPU limited using a 4000+.Avalon - Tuesday, November 23, 2004 - link
Anand, you keep saying that a 6600GT in SLI outperforms a 6800U in Doom 3 and HL2, but your benchmarks look partially wrong to be concluding that. It seems it would be more correct if you said that a 6600GT in SLI outperforms a single 6800U in lower res, lower bandwidth situations (such as 12x10 with low AA/AF, or less), but in high res and bandwidth situations (such as 16x12 with a bit of AA/AF), the 6600GT doesn't appear to be able to keep up at all with a single 6800U. Buyers will need to take that into consideration, to make sure that the video setup they will be purchasing will meet their needs specifically.lifeguard1999 - Tuesday, November 23, 2004 - link
One simple question: Are there Linux drivers that support SLI?Historically, people have talked about a setup either being CPU bound or GPU bound. That is no longer the case. With SLI it appears that the limiting factor is data. Simply put, there is not enough data for the dual GPU's to render. This is a common problem in parallel programming, especially when you are talking about thousands of processors. By increasing the amount of data for the GPU to render, one can see that SLI performs better.
For example, at 1600x1200, the increase is only 20% going from simgle 6800U to 6800U-SLI. Now by increasing the amount of work for the GPU to perform (1600x1200 with 4X AA and 8X AF), the performance increases 48% going from simgle 6800U to 6800U-SLI.
What this means is that game developers can now have Low, Medium, High, Ultra, and Ultra-SLI rendering modes in their games. :) What a nice "problem" to have.
In my line of work (Scientific Visualization) where we can have models up to hundreds of millions of polygons, SLI is going to cause a revolution in how we do business.
Alphafox78 - Tuesday, November 23, 2004 - link
wow, if I my LCD went to 1600x1200 SLI might help me slightly... I wonder what % of people actually play with the res that high. at 1280x1024 with my 6800GT AGP overclocked to ultra speeds with 4x aa and 8x anistropic I noticed no slowdowns in the game, smooth as can be for 95% of the game.GhandiInstinct - Tuesday, November 23, 2004 - link
Yes, great performance increase, but its too expensive to afford for most people. Unless you're 3 generations behind and need a new system chances are you'll buy this but not for people that have stabe up to par systems. This just isn't a wise investment when ATI's multi-gpu technology is right around the corner which doesn't limit you to the inferior Nvidia.OriginalReaper - Tuesday, November 23, 2004 - link
I dont see why 8xAA wasn't used. It's clearly not GPU limited at 4xAA 8xAF.blckgrffn - Tuesday, November 23, 2004 - link
I am glad that NVIDIAs drivers seem fairly mature already, hopefully they will have a new release out by the time SLI becomes "mainstream". It would have been awful had this real release been tainted by a lot of driver issues. So, the real point here is that if you really want performance, you have to drop $800 at some point? Wow. Two 6600GTs already are not the optimum choice for 1600*1200, so a 6800GT is what should be purchased now if you are really all about fps. Hmmm. I suppose I do know people who would like the incremental upgrade path, but I am not one of them when it comes to graphics cards - I sell my "old" one just before the new product cycle really starts appearing in quanities on the shelves and go for the new technology, and I am guessing that many who have $800 to spend on graphics cards would do something similar. I am jealous of those who will be able to spring for a big-power SLI setup out of pocket...dak - Tuesday, November 23, 2004 - link
I'm curious, is it possible to use two PCI-X video cards in these SLI boards, but not have them configured SLI? I have some applications that would benefit greatly from having two high end dual output cards in a single computer.....shabby - Tuesday, November 23, 2004 - link
Great article Anand, can you mention which psu you used to feed those hungry 6800 ultra's?Aquila76 - Tuesday, November 23, 2004 - link
Looks like SLI'd 6800GT's are a great option for now. I'm greatly awaiting ATI's Multi-Rendering products now. Can't wait for that benchmark setup!