Legit Reviews

Posted: **Mon Sep 29, 2008 7:19 pm**

I have a 9800GX2 as my primary graphics card. I've posted here about my CAD application, Rhino 3D, not running very well because it renders its content on my secondary 7900GTX card even though my 9800GX2 is the primary. It seems to affect OpenGL only, as when I activate the DirectX9 plugin for Rhino, the stutters, hangs and generally bad performance go away.

I confirmed my suspicions today because a friend of mine is a CS major and is working on learning to write graphical apps in OpenGL. His app, along with Stellarium (a free planetarium-type app) freeze on load for minutes on end. Even when "unfrozen," performance is akin to a slide show.

Direct3D/DirectX applications and games do not suffer from this problem. However, OpenGL attempts to render on the wrong card. I have a feeling it's because the 7900GTX is listed first in the device manager, despite the 9800GX2 being my primary. The 7900GTX is not even in a full-speed PCI-E slot. The 9800GX2 is in the primary slot.

Is there something I can do to force OpenGL content to render on the right card? When I disable the 7900GTX in the device manager, all problems disappear. However, that shuts off my second monitor as with a 9800GX2 in dual-GPU, we've all done the SLI-one-monitor-only song and dance before.

Posted: **Tue Sep 30, 2008 3:11 am**

The 180 'big bang' drivers should be right around the corner, and one of the things they do is enable multi-monitor support in SLI mode.

So if you don't find a hack, a fix is due any time now.

Dan

Posted: **Tue Sep 30, 2008 10:38 am**

...if Big Bang II ever appears.

Posted: **Thu Oct 23, 2008 9:37 pm**

UPDATE: SOLUTION!

If (very unlikely) your situation matches what I describe below, the solution is simple: INSTALL THE 180.42 DRIVERS! You may have to use a modded INF, but the OpenGL performance will be what it should be. Short version: Two NVIDIA cards (usually a DX10 paired with a 7-series) and multiple monitors, at least one plugged into each card, brings horrible OpenGL performance. Installing new drivers fixes the problem.

Sovereign, a long time ago... wrote: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).

This post at the OpenGL forum pointed to drivers as a solution. My original guess on the "rendering through the other card" was incorrect. I can confirm that with a 9800GX2 and a 7900GTX, OpenGL based apps like Rhinoceros and Adobe Photoshop CS4 Extended work great.

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