I know many are skeptical regarding how Oblivion handles Multi-GPUs. I was always a multi-card supporter and believed there was a boost in performance when using two cards. But at times I even doubted if I was actually seeing real FPS gains when using SLi. Well, my doubt is no more. I am certain now that Oblivion does gain from Multi-GPUs. It just took some trial and error testing to prove it to myself.

Many are aware by now of Nvidia 3D Vision. I found that when I disabled 3D Vision thru Nvidia Control Panel, I see an FPS loss of about 15 - 30 FPS depending on what is being rendered on screen. A LOSS? Now this really intrigued me. If anything, disabling 3D Vision would surely cause a gain in FPS as 3D vision can be rather taxing on a GPU.

Now in contrast, when I enabled 3D Vision, I saw a boost in FPS by 15 - 30 FPS. Is it possible that enabling 3D Vision is in fact forcing better SLi scaling for Oblivion? After all, 3D Vision is a GPU demanding feature and was heavily developed to utilize mult-GPU environments.

With that said, I can only assume there is a way to use a 3rd party driver tweaking program to force SLi scaling for Oblivion. Perhaps through CoolBits/NVTweak or something similar.

UPDATE: Please see post below by ArmeniusLOD. It's been discovered that even if you don't have the 3D Vision kit, you can still install the 3D Vision drivers on Nvidia cards to force the performance boost for you video card. I also assume that even one video card might gain from this little trick.

Anyone have any opinions or ideas on this? Also would be cool if others can test to verify this discovery. Hard FPS numbers would be awesome!

Just for the record, I was doing this test with SLi enabled.

That's an interesting find, I'll have to test this myself. nVidia drivers do include a custom SLI profile that is used when the game is run, but the fact is that Oblivion does not scale well with SLI due to the engine being heavily CPU-bound. Running GPU-Z in the background while running Oblivion, I observed that the game only uses 15-20% of my graphic cards, while it uses around 80% of Core0 on my CPU.

I never doubted the performance gains of SLI. When I first built this computer I had forgotten to install the SLI bridge, so only one card was being used. Doom 3 was the first game I ran, and I set the FPS timer to -1 to unlock the framerate and change the counter factor to time-based instead of frame-based. At 1920x1080 on Ultra quality with just the one card I was getting 50-60 FPS. Adding the bridge and enabling SLI in the drivers increased the framerate to 90-110. Typically the framerate gains are 50-70% in games that scale well, but Oblivion is typically only 15-20%.

Update: Well I'll be damned, it actually works. I didn't do any thorough testing, but I immediately noticed how much smoother the framerate was. I was running OSR with a frame cap of 40, so I didn't look at the exact numbers, but the smoothness and consistency were great. I would have never thought to check such a thing.

For those who want to try this, the drivers will want you to setup your hardware first. If you don't have 3D hardware, just choose "3D Vision Discover Glasses," pick the second box in the first part of question 2, pick the first box in the second part of question 2, and then select the first box in the last screen. In the driver control panel, check the box that says "Hide stereoscopic 3D effects when game starts." You will get the benefit of the performance boost without the anaglyph picture. If you do get the anaglyph picture, simply press CTRL+T to toggle it. You have to have installed the 3D VISION driver when you installed the latest driver package for it to work.

My theory for why this happens is because the 3D driver forces the game to use more GPU power to process the stereoscopic or anaglyph rendering. As a side effect, performance is increased for this game which almost exclusively uses the CPU.

Yes, I agree with your theory. It would be awesome if you could give some hard numbers with and without 3D Vision enabled. I will do the same as well.
If the numbers are good enough, this may be a nice little performance boost trick for others who might be thinking of building a new computer but could simply purchase a second video card instead. Assuming nothing on there system would bottleneck a 2nd GPUs performance gains.

EDIT: just edit the max FPS in your OSR.ini file. The max allowed is 200 FPS. This will allow you to see the full benefit of running both cards with 3D Vision enabled.

I find that to be unlikely. nVidia has likely pushed their per game optimizations as far as they can go. I find it more likely that, because 3D Vision requires a stereo pair of images, the GPU must render two images per frame; Oblivion may be getting a report that it is rendering more frames per second than it was before, which is probably technically true. However, what Oblivion may not realize is that each frame is actually one half of a complete stereo image.

So, why is it that Oblivion can render more frames when they're stereo then when they're not? All that the GPU has to do is perform a quick translation of the game world to render the second frame of the stereo pair. No models move, no additional textures have to be loaded, all it is is a second and nearly immediate render.

As such, the GPU can push out a few more frames than usual because it doesn't have to wait for Oblivion to update the game world between the two stereo pairs. So, if Oblivion says 60 FPS, you may in fact, be getting 30 pairs of stereo images per second.

I have tested Vanilla Oblivion with various scenarios. Please note that I saw the FPS boost under a modded Oblivion load order. I will post additional screens after I add all my mods. This will give us a better idea how well SLi performs versus a single card, and if the 3D driver is making a difference.

So far I've found that with 3D Vision enabled, it forces the game to sync frames (Vsync) This probably accounts for the smoother game play ArmeniusLOD reported

1. http://i295.photobucket.com/albums/mm150/far327/singlecard.jpg
2. http://i295.photobucket.com/albums/mm150/far327/SingleCard3DEnabled.jpg
3. http://i295.photobucket.com/albums/mm150/far327/SingleCard3DEnabledandActive.jpg
4. http://i295.photobucket.com/albums/mm150/far327/SLI.jpg
5. http://i295.photobucket.com/albums/mm150/far327/SLI3DEnabled.jpg
6. http://i295.photobucket.com/albums/mm150/far327/SLI3DEnabledActive.jpg