Created attachment 69414 [details]
Example of artifact

Hello!
Please look at attached screenshot - there is triangle where we still see part of old frame, that was displayed on screen few frames before. I doesn't sure about terminology, but from my point of view looks like rendering in this triangle is lag behind rest of the screen.
This issue happen for me only for applications launched with enabled offloading rendering (DRI_PRIME=1). It's reproducible not only in "Left 4 Dead 2" but also in other applications. Even in Chromium (if you launch it with "--ignore-gpu-blacklist" option that enabled hardware rendering on Mesa, and "DRI_PRIME=1" that enable offloading rendering) display same artifact (triangle) while scrolling pages. Also you may notice this artifact in glxgears, if you you run it in fullscreen mode.

Software:
Kubuntu 12.10 x86_64 updated from Xorg Edgers PPA.
Mesa: 9.1~git20121029.00e6819e
libdrm-radeon1: git20121025.bc494b31
xserver-xorg-video-radeon: git20120928.e8cb0b72
xserver-xorg-core: 1.13.0+git20120920.70e57668
Enabled or disabled V-Sync in KWin settings doesn't make the difference.
Enabled or disabled V-Sync in game settings doesn't make the difference.
Screenshot taken with stock Kubuntu kernel (3.5.0-17). With 3.7rc3 kernel issue still reproducible, but just a bit less noticeable.

Hardware:
Acer Aspire 7560G laptop,
AMD APU A8-3500M with integrated Radeon HD 6620G (SUMO)
Discrete AMD Radeon HD 6650M (TURKS)

"xrandr --listproviders" output:
Providers: number : 2
Provider 0: id: 138 cap: 0xd, Source Output, Source Offload, Sink Offload crtcs: 2 outputs: 3 associated providers: 1 name:radeon
Provider 1: id: 85 cap: 0xd, Source Output, Source Offload, Sink Offload crtcs: 6 outputs: 0 associated providers: 1 name:radeon