You can do it without Nvidia, too, you just need to enabled Xinerama. With NVIDIA it’s better to use their proprietary system (I foget what it’s called at the moment).[/QUOTE]
Of course, there’s no easy way to know which GPU is on which screen.
Sure about that? You can specify Devices with PCI IDs, and Screens to use specific Devices. Precise control of which GPU is which screen IIRC. Also, with separate screens, there’s (according to NVidia) very little overhead for this. And no vaguery of which GPUs get which textures/etc. as with TwinView/Xinerama.
If you know how the xorg.conf is setup, that’s true. I was referring to the general case of having two screens set up, and trying to figure out though X calls what sort of GPU is bound to each screen before you create a context.