https://bugs.freedesktop.org/show_bug.cgi?id=35697
--- Comment #5 from Nikos Chantziaras realnc@gmail.com 2011-03-27 12:58:35 PDT --- (In reply to comment #4)
lets blame page flipping until proven otherwise for any 2.6.38 problems ;-)
Can you try disabling page flip?
Option "EnablePageFlip" "FALSE" in xorg.conf device section.
Indeed that fixed the problem completely.