Question is why can't apple get crossfire working in osx or some other variant to enable dual gnu usage system wide? ...
From what I understand....
Games can take advantage of a second GPU without crossfire for things like Physics, some shader effects like smoke, turbulence and hair dynamics, fluids etc but the game developers have to write that code themselves. ...
There are two ways in OS X for multi-gpu support. One is through using OpenCL. In a game that might be useful for game logic and physics behind the scenes (assuming that the memory bandwidth doesn't kill the performance gains you're trying to get). The other way is that a form of Crossfire/SLI IS supported in OpenGL, called "offline rendering". You can specify frames to be rendered "offline", i.e. on a GPU that isn't connected to your display. It's not a huge amount of work either, but the difference is that where Crossfire/SLI is automatically applied, in this case the game developers have to write code to manage this.
Which, actually, is better. The developers can fine tune the frame pacing for the best performance. However the down side is they have to do something, so basically it never happens. Projects cost millions of dollars and are always understaffed. AMD has the better GPU architecture, but again it takes some work on the developers part to get the performance out of that, whereas Nvidia is just brute force, but easier to program for. Guess which GPU's games generally run better on? Nvidia of course, but they're hotter and louder for that.
So it's one of those things where the Mac certainly
could be a much better platform for gaming than Windows technically, but Windows wins because it's easier and it has the history. Also obviously Macs are impossible to upgrade sufficiently for bleeding edge performance.
I'm a "professional", and I like to play MMO's only, Lord of the Rings Online and possibly Skyrim when it comes out, both of which are Mac and PC. For LOTRO I have my 2009 Mac Pro relegated to near permanent Windows 7 duty. The Mac client is buggier, it crashes after an hour (they claim it is because I have the settings too high but they clearly have a memory leak they don't want to bother fixing). Anyhow on Windows I can get a few things. First is Eyefinity, so I have three monitors hooked up for glorious widescreen gaming. Two is the latest AMD drivers. They've been working on these like crazy to fix the frame pacing issues, and let me tell you this last one made a huge difference. Buttery performance most of the time at 40-60 fps. The driver also manages clocks, fan and other factors that OS X won't touch.
When my new Mac Pro comes in I'm not sure what I'll do. I have 3x 27" monitors hooked up to it, and with the D700's/hex it'll surely be a treat. Under Windows only though, and I hate rebooting my work computer. I'll try those games under Mac just to see, maybe LOTRO won't crash now with 6GB VRAM. But it'll be single monitor only.
And there's further complications ... AMD is addressing frame pacing for Eyefinity users now. What in the heck does three monitors mean with the nMP? Do two connect to one GPU, and one to the other? Nobody knows how the video is multiplexed. I suspect that IOSurface is automagically doing the offline rendering as I indicated above, instead of it being a purely hardware solution, but I don't know. Regardless for Eyefinity all monitors need to be physically hooked to the SAME GPU, which I suspect isn't the case with three monitors on two TB busses on the nMP (what about if they were on three busses?)
Too many questions, too goofy, I could get better and easier performance by spending $2k on a custom gaming rig.
