Poor game performance with dual displays - (2007.06.28)
This was happening most notably with Doom 3, using my brand-new NVIDIA GeForce 8600 GTS,
under Windows XP and a Core 2 Quad. The framerate should have been flying. At "High detail"
and 1280x1024 resolution, with v-sync disabled, my old P4 3.2 GHz was getting 57 frames
per second, but the best I could get on the new machine was only about 34 FPS.
Solution? It turns out that the newer NVIDIA display drivers have a performance-mode setting
that allows you to select between "dual display" and "single". Setting it to single fixed
it, and I was able to get 114 FPS. I don't know for sure, but I presume that it was trying
to render both displays at the full framerate even though the game runs on only one display.
I haven't seen any other impact of changing this setting. Only a restoration of the expected
framerate in my games.
(framerates were tested by using Doom 3's "timedemo demo1" console command, and running it
at least twice to get a more reliable number)