Installed driver package version: 2:2.99.910-0ubuntu1 OS: Ubuntu Studio 14.04. Tried with XFCE compositor enabled or disabled. I get screen tearing when scrolling in Firefox, moving windows around, etc.
The XFCE compositor doesn't prevent screen tearing, and by default all frontbuffer rendering in X is allowed to tear. If you want tearfree operation, you have to specify Section "Device" Identifier "Device0" Option "TearFree" "true" EndSection in your xorg.conf (or snippet under /etc/X11/xorg.conf.d/tearfree.conf).
Thank you, it works fine now. The performance of vblank_mode=0 glxgears is still fine with this setting, so it doesn't give any noticeable performance hit either.
After enabling that option I have had some occassional serious problems with areas of the screen not getting invalidated (what is the linux terminology?). Areas appear black or retain whatever was there right before. Do I open a new bug?
Sure, it will just be a bug in the damage tracking. Be sure to check for updates whenever you encounter such a bug. When you do, please file a new bug, describing what application was affected and attach your Xorg.0.log.
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