Has Apple possibly enabled Crossfire X under OS X?

[goMac]

Well that's very interesting, thanks. I can't find the video, even from my Apple Developer paid account they only have WWDC videos going back to 2011. If anybody has a link to the video that would be helpful. However I did find this technical paper on adding multiple GPU Open GL support.

So I wonder if OSX itself is using this, and that's how they spread graphics work across multiple GPU's in the nMP? That would only work for the Window manager in OS X (Cocoa graphics) and not games which write OpenGL itself.

If I had time and more interest I might author a OpenGL library which makes it easier for game developers to get multiple OpenGL GPU support in OS X. Sort of a open source Crossfire or SLI.

https://developer.apple.com/videos/wwdc/2010/

 

[Cubemmal]

https://developer.apple.com/videos/wwdc/2010/

Thanks, my earlier searches came up blank. Even then I had to jump through some more hoops to get it into iTunes, grr....

 

[antonis]

I think that nMP is quite a niche machine in the first place and Apple has taken a considerable gamble by focusing so much on GPU computation. Well, thats what I like about Apple - they are not afraid to take risks Of course, this all depends on whether developers of professional software will be committed to harness all this GPU power.

Indeed If anything, in Apple's ecosystem we can never get bored. I also like that they are not afraid to change the game rules and risk. It's just that sometimes they make us wonder where we stand. But that's just part of the game.

Cheers to a nice future for nMP on OS X side.

 

[Cubemmal]

OK I watched the WWDC video. Advantage is that it works across heterogenous GPU's - Vendor or make. Disadvantage is that all synchronization is mediated by host memory. That is, to get a texture from one GPU to another it has to be copied to host, then copied to the other GPU. Crossfire is GPU to GPU. Additionally he interestingly warns about Display bottlenecks. Which is don't feel like you have to render and display every frame. Not sure about that comment.

However perhaps this can be mitigated by double or triple buffering, as they seem to note. Another thing to note are demos where they show doing OpenGL on one card (rendering), and Open CL on the other (particle swarm). This is probably the ideal use case, as it very cleanly separates out the workflow in a natural and partitioned way.

Finally they talk about IOSurfaces, which handle resource sharing automatically. I'll finish and note that OT, this would be the way they can enable Crossfire like support in OS X. The IOSurface job is to manage resources across GPU's and CPU's. If they recognize that two GPU's need to share something, it can be done automatically here.

 

[Cindori]

Crossfire will cut your available VRAM in half (since it's mirrored across the cards), so it's not really effective for Pro use cases. It's better for the Pro apps to take advantage of each GPU simultaneously.

 

[goMac]

Finally they talk about IOSurfaces, which handle resource sharing automatically. I'll finish and note that OT, this would be the way they can enable Crossfire like support in OS X. The IOSurface job is to manage resources across GPU's and CPU's. If they recognize that two GPU's need to share something, it can be done automatically here.

Yep. In theory, if you copied all resources onto each card (which yes, would cut your VRAM in half), did a render of half a frame on one card, and a render of the other half on the other, and then pushed the half renders together onto the display card with an IOSurface, you'd have basically Crossfire running under OS X.

Heterogeneous GPUs are very very interesting, but you'd have two potential problems from what I see...
1) If the performance is different, you've got to do some sort of load balancing.
2) If the GPUs have slightly different output that will get more noticeable.

The OpenCL/OpenGL combo for two cards is basically what Apple is strongly pushing today, and shipping in apps like Final Cut Pro X. Also a good way of going about it if your app has strong OpenCL and OpenGL requirements.

I'm also wondering if perhaps under the hood IOSurface is now using whatever sort of bridge Apple has put onto their cards in the Mac Pro.