Window tearing with kubuntu 1210 beta2

[John_kubuntu]

Using Intel sandy bridge graphics 2500k processor.

When I move a window horizontally the top part is displaced 2-5 mm depending upon the speed of moving.
This only occurs with the part of the window that is above a certain height on the screen
(above 5/6 th of the height of the screen).
This does not occur in kubuntu 12.04.

The effect disappears when I turn off vsync in System Settings - Desktop Effects.

I tried to provide this feedback on the kubuntu wiki feedback page.
But I am unable to edit that page, even after registering and logging in....

[UPDATE]
I played a bit more with my current 12.04 installation.
The tearing also occurs there, but only in the very top part of the display (about the width of a window's titlebar).
That's why I did not notice it before!
might well be some timing-critical code path that changed in the intel driver....

[SteveRiley]

What's the output of

grep -i sna /var/log/Xorg.0.log

[John_kubuntu]

Steve thanks for looking into this.

The string sna does not appear in my /var/log/Xorg.0.log
I attached the file to prevent waste of time.
Do you see anything out of the ordinary?

(ps to be able to upload I had to rename the log file to have an extension .txt...)

[SteveRiley]

The newer Intel graphics driver enables SNA acceleration by default, which might eliminate your tearing. You have a couple options.

First, try enabling SNA with your existing driver. Create the following minimal /etc/X11/xorg.conf:

Section "Device"
 Identifier	"Intel Graphics"
 Driver	"intel"
 Option	"AccelMethod" "sna"
EndSection

Reboot, and then check for "SNA" in the Xorg.0.log file.

The second option would be to use an experimental updated X stack with newer drivers. Personally, I use this all the time, and it works fine for me. But others have reported varying levels of success, from total instability to unicorns and rainbows. So try the first option and report back. If it doesn't help and you want to try the second, let us know, and we can help you.

[John_kubuntu]

I tried already a newer stack with fedora 18 alfa, see the bug that I reported here:
https://bugs.kde.org/show_bug.cgi?id=307965
Will try the SNA experiment and report back...

[John_kubuntu]

Enabling SNA in fedora 18 preview succeeded, but it did not alleviate the problem.
See the bug report on bugs.kde.org.
I am waiting for suggestions from the developers and I will report any progress back in the bug report.