I am trying to do multi-gpu work on Linux, using specifically 2 k4200 quadro's. I have attempted to use SLI, but even after changing the X11/xorg.conf file using nvidia-xconfig for SLI to be SFR, it doesn't seem to be using the 2nd GPU (glmark2 tests I've tried remain in the same ballpark). So first question is how do I enable SLI for these cards in Linux? Is it even possible?
If it's not possible, I was wondering if I can manually split the work & perform offscreen rendering on each GPU. However, is there a Linux/X11 equivalent of wglEnumGpusNV to get list of available GPU's? Also I was hoping to use glXCopyImageSubDataNV to copy data from one GPU to the other. Does that data transfer go through the CPU (i.e. slow) or does it go directly between the GPU's?