Starting with the Nexuiz test profile we ran this OpenGL-powered game at five different resolutions: 800 x 600, 1024 x 768, 1280 x 1024, 1680 x 1050, and 1920 x 1080. These results were rather quite interesting with a large delta between Ubuntu and Mac OS X when running at the lower resolutions. Both Ubuntu 9.10 and Mac OS X 10.6.2 were running at 1920 x 1080 by default, but with Snow Leopard there seems to be a bug when running the games at a different resolution from what the resolution is set, that at times Mac OS X is dropping back to software acceleration or its GPU stalls at times. We had not analyzed these results until after all of our Mac OS X and Ubuntu testing was completed, but we went back to look at this matter closer. We found out that this wasn't a Nexuiz-specific issue but is affecting all OpenGL games we tested. Below as another example you can see the performance with the ioquake3-powered OpenArena game.
With OpenArena, 800 x 600 actually had the worst performance by far at just about 15 FPS, almost to the speed of Mesa's software rasterizer on Linux. The performance with OpenArena had not peaked until running at 1280 x 1024 when from there the performance decreased with the resolution bumps, as it should.
After seeing these results, next we set Mac OS X to mode-set at 800 x 600 from the display area. When the resolution was changed from 1920 x 1080 to 800 x 600 we re-ran OpenArena at 800 x 600. Sure enough, we had over 130 FPS and these problems were eliminated. There is clearly a problem going on with Snow Leopard even with the latest 10.6.2 release.
To further illustrate this issue, we recorded a video of when Nexuiz was running at 800 x 600 and immediately after that when it was running at 1920 x 1080. When at 1920 x 1080 it was running over twice as fast and you can see the frequent lag and GPU stalling when at the lower resolution. Below is this video (jump to about 2:00 into the film to start). Again, this was reproduced many times under Mac OS X 10.6 when using the NVIDIA graphics driver with the GeForce 9400 graphics processor found in the Apple Mac Mini.