I'm forwarding this bug from a Ubuntu reporter.
With a Dell D6340 laptop + external monitor setup arranged side-by-side, if you rotate the external monitor but leave the LVDS un-rotated, and if the resulting width goes beyond 2048, there will be a major performance slowdown.
It does not seem to matter if the rotation is done via xrandr or in the xorg.conf. Switching between EXA and XAA makes no difference. Turning off DRI or setting NoAccess to true makes no difference. Turning the laptop screen off makes no difference.
If the displays are arranged such that they fit into 2047 width, it works perfectly. Moving it 1 pixel to 2048 suddenly causes the performance problem. If no rotation is performed, the displays can be side by side with width > 2048 with no performance issues.
00:02.0 VGA compatible controller : Intel Corporation Mobile GM965/GL960 Integrated Graphics Controller [8086:2a02] (rev 0c) (prog-if 00 [VGA])
Subsystem: Dell Unknown device [1028:01f9]
zhenyu, is this known behaviour?
Could you try current 2.3.1 driver? There was some 2048 size kludge on 965 hw that should be fixed now.
ping for response...
Ah, sorry, the original reporter confirmed it fixed on the ubuntu bug:
== Vu Ngoc San wrote on 2008-06-06: ==
now it works ! thanks!
next step would be to make compiz work with rotated external monitor...
But that's probably a completely different issue.
(it doesn't work even for virtual screen less that 2048x2048, for new and old driver. The external screen becomes black when compiz is enabled. All I can see is the mouse cursor :) )
anyway thanks again a lot for this fix.
== Bryce Harrington wrote on 2008-06-20: ==
Great, thanks for confirming the fix - I've got 2.3.2 up in intrepid now so we should be good to go.