I've a setup with two graphic cards and tree monitors: one monitor on one card and two monitors on the other. It is working fine in Windows, but in Linux graphical performance is really slow. Moving windows around is slow (sometimes it even leaves a trail of windows behind), typing delays with half a second before the text is displayed, etc. The X process is also using a lot of CPU: idle 35% (on a PhenomII X4 965) and when doing things it gets up to 70-90%. When I posted my problem on the ubuntuforums, one
person reacted that he has similar issues.
I've tried a twinview over the two screens on the first card and then a seperate X screen on the second card (doesn't work, KDE sees the first two monitors as one and fails to maximize, also the performance problem), three seperate X screens with Xinerama (the performance problem) and without Xinerama (KDE running on just one screen). I'm fine with not having KDE on the third screen, but I want it on at least the two screens. It's working perfectly fine when I disable one of the cards.
I'm currently using Debian Testing, but I've also reproduced the problem on Debian Stable (Squeeze), Ubuntu 10.04 and Kubuntu 10.10. I'm running the 2.6.38-rc2 kernel now, but all the other kernels I tried also give problems. Latest driver version: 260.19.36. I'm willing to try newer kernels and/of drivers
Hardware is a 9500GT as primary card with two 1920x1200 24" displays and a GT 210 as secondary card with a single 1680x1050 21" display.