Poor Crossfire Performance

[walktexranga]

Hi Guys,

 

Rig: [email protected] | 12 gig | 2 x 5870 | 120 Agility 3 | Win 7 64-Bit | D5 & XSPC W/C

 

Ive tried many varients of ATI drivers..

 

with crossfire enabled I get 30-60fps with it disabled I get 50-60fps..

 

Any ideas?

 

Cheers!

[ProjectVRD]

The game would appear to have not been coded to run on more than one GPU, it essentially has no nVidia Cuda and AMD Stream tech implemented. Although other games didn't have this stuff used in their games, they did provision for the use of more than one graphics card so Crossfire and SLi could be made to work with a little bit of effort. But with both nVidia and AMD struggling hard to get anything acceptable happening with this game it would appear Bethesda didn't code anything in for whatever reason.... perhaps time constraints? We can only hope that Bethesda decide to try and address this in a future patch because both Cuda and Stream kits are available freely for them use at their discretion. Both nVidia and AMD have gone as far as hardcoding some magic into their drivers which is extremely rare, their latest rounds of driver updates provision exactly for Skyrim instead of the usual simple updates but that can only do so much... they still need the game developer to pitch in and do it's part. Ultimately in an ideal situation it would be the game itself that delegates what cards should be rendering what leaving the hardware to purely dedicate it's resources to working on the instructions they recieve instead of analysing and deciding that for itself, after that the next best option is for the game to tell the CPU to take care of the of splitting the dtata and then tell which of the GPU's should do what which is the overwhelmingly popular option gaming companies take. Nowhere near as efficient but that is what they go for because it is less work.

 

An ultimate multi-GPU compatible game would not query the CPU at all, it would just delegate everything to the cards in a manner where each card gets seperate instructions thus bypassing the processor, and the processor would then only be given information by the cards after it has been rendered which is really how all GPU cards were designed to do on a hardware archetecture basis. Only one game seems to do this... and it isn't even available yet. It is called CARS and it is being built by enthusiats who set up a sort of limited company to build it, these enthusiats have also worked on games themselves so they have experience to pull it off. The game engine is expected to have direct communication with the graphics cards no matter how many, and the game engine will be splitting the work load itself before sending it to the hardware leaving the hardware near zero overhead for non-randering purposes. Both GPU, and then CPU, will freed to work their magic in efficient way we have not yet seen. I don't expect Bethesda to ever take this route, I wouldn't be disappointed that they won't neither... nobody does it this way.

 

What the manufacturers have managed so far with Skyrim would therefore appear nothing short of a little miracle, at least as far as just two card Multi-GPU systems are concerned. They can produce above ultra settings at 1080p with HD mods at 55fps-60fps, but then there will be periodic (read more like regular) stutters where it will go down to about 15fps for 2 or 3 seconds before returing to 55fps-60fps. It is a good effort but that is likely as far as they can take it which is a shame, both card companies have moved heaven and earth to get it running as best as possible... 3 and 4 card multi-GPU suffer much worse than 2 card multi-GPU setups because of the way scaling works, the splitting of information for each card to render into an image. And that is clincher here, that missing bit of code is all about how the game engine and CPU talk to each other in terms of scaling the performance between more and more cards as seen in the majority of modern games. At the moment, it is all card and not the game or the CPU doing the work delegation. These gaming cards weren't built to handle that kind of workload on top of rendering the information they recieve... the only cards that are built to handle such a momunental task are the 3D design graphics cards but ofcourse they are only good at rendering 3D models in a CAD environment... not rendering them on the fly from already predetermined markers like in games. And even then the CAD software is coded to leave out the CPU and talk directly to the AMD or nVidia's installed in the machine. They cost about £3000 so even if they had the right chips designed to play out a game into a moving realtime image they wouldn't be affordable.

 

Have hope, Bethesda may yet come to the rescue and if they help fix the problem... with a creation kit already being out... this game will then look insanely good! Always an optomist! :thumbsup:

 

 

PS. I really should add that this is just conjecture, although it comes from what I regard as good source considering I have known the person who explained what he believes is happening. He codes for games and we first met in college etc etc etc... it may not be the real cause, but I am in no position to tell him he is wrong lol.

Edited February 1, 2012 by ProjectVRD