I recently built a new desktop with an AMD A10-6800K (Radeon HD 8670D) APU. Basic graphics performance was fine with the open source drivers, but I installed fglrx* because I wanted to enable sound through the HDMI port.
It works like a charm for playing videos (no problem with fullscreen 1080p), but today I decided to try playing Supertuxkart for the first time on this machine. The result was very poor - the sound was choppy, the video lagged, and even moving the mouse around on the setting screen was jumpy. Oddly enough, my system monitor was not showing particularly high CPU or RAM usage at the time.
If anyone has any suggestions on sorting out the gameplay issues, I'd appreciate it. The only things I can think of are trying out the open source drivers (which cuts off the sound output to my tv) or the beta driver from AMD, but maybe there is some other configuration I can try.
*I installed the (non-beta) drivers from the AMD website since both fglrx and fglrx-updates in the Ubuntu repos were showing an "unsupported hardware" watermark, but this didn't come up with the one from AMD. I've also enabled hardware acceleration.
Other info: even running glxgears causes trouble. It's fine in the small window (and even returns over 1500 fps) but enlarging the window causes the framerate to drop (to a still-respectable 200 fps) but the playback becomes choppy and again, the mouse cursor no longer moves smoothly. It seems like this is probably an overall openGL issue.
Update: using the fglrx-updates package from the Ubuntu repositories gives much better performance, but leaves me with an "unsupported hardware" watermark. The open source Radeon drivers work OK for video and display management, but leave games like Supertuxkart unplayable.