I have two videocards in my system (NOT SLI/CrossFire): a 9800GX2 in Dual-GPU Mode and a 7900GTX for my second monitor. The problem is that any OpenGL based application (such as Blender, MeshLab, Stellarium etc.) runs horribly! All Direct3D content using DirectX9 or DirectX10 runs butter smooth. Why? I looked in Rhino 3D’s options menus, and it confirmed that it was in fact rendering all output on the 7900GTX graphics card even though the application was loaded on the primary monitor connected to the 9800GX2! Moving the window to the other monitor did not alleviate the problem, as the 7900GTX does not up-clock properly so the core is stuck at 275MHz (instead of 650MHz). The only solution I have found is to disable the 7900GTX if I need to run an OpenGL application. This has the unpleasant side effect of shutting off my second monitor. Then the application runs beautifully on the 9800GX2; however if the 7900GTX is there as an option, every OpenGL application tries to use it while simultaneously displaying on the 9800GX2 controlled monitor, resulting in aforementioned performance issues, which include excruciatingly slow rendering, applications “Not Responding” and applications using huge amounts of CPU time but ultimately freezing and requiring an End Process in the Task Manager.
My operating system is Windows Vista Ultimate x64 Service Pack 1 with all the latest updates. I am using the latest NVIDIA drivers. I’ve tried every option in the Multi-Display/Mixed GPU Acceleration options; they’re all equally bad performance-wise (but again only in OpenGL).
I’ve experienced the exact same problem trying to run three monitors on my sytem (also vista ultimate 64bit). I have tried contacting nvidia and have filled out their vista quality assurance form for every beta and release driver they produce, but the issue keeps being ignored.
I have had the exact same horrible performance with both a 7950gt+8600gt and with 9600gt+7950gt.
The applications are not rendering on the 7900 and displaying on your 9800gx2 causing the slowdown… but rather than the opengl implementation properly exposing multiple rendering devices, it mangles together both adapters into a single device (which doesn’t work due to corruption from overwriting the internal data structures w/ the 2nd adapter’s information).
meanwhile, when I try and render w/ open GL… my Q6600 pegs at 50% load on all four cores, while rendering less than 1 frame per second… slower than software rendering.
Long story short, nvidia doesn’t care to write functioning drivers - they probably figure they can get you shell out for a 2nd 9800gx2 to replace your 7900gtx. I wouldn’t get my hopes up of them ever fixing this issue. Though, if you can live w/o aero-glass and dx10, you might want to try 64bit XP drivers.