Dual head in unity very slow updating display

[Colin Law]

Binary package hint: unity

On a new install of 11.04 (updated) when Unity is used with a dual head display in extended desktop mode display update is very slow. If I drag a window nothing happens for several seconds then the window jumps to the new position.
Running top shows compiz consuming around 30% CPU even when nothing is happening (except top). When a window is moved this goes close to 100%,
Monitor resolutions are 1280x800 and 1280x1024.

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: unity 3.8.10-0ubuntu2
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic i686
Architecture: i386
CompizPlugins: [core,bailer,detection,composite,opengl,decor,mousepoll,vpswitch,regex,animation,snap,expo,move,compiztoolbox,place,grid,imgpng,gnomecompat,wall,ezoom,workarounds,staticswitcher,resize,fade,unitymtgrabhandles,scale,session,unityshell]
CompositorRunning: compiz
DRM.card0.LVDS.1:
 status: connected
 enabled: enabled
 dpms: On
 modes: 1280x800
 edid-base64: AP///////wAyDADIAAAAAAAQAQOAIRV4CrNwmVlTjScjUFQAAAABAQEBAQEBAQEBAQEBAQEBthwAuFAgJTAgKEQAS88QAAAZAAAAAAAAAAAAAAAAAAAAAAAAAAAA/gBMR1BoaWxpcHNMQ0QKAAAA/gBMUDE1NFcwMS1UTEU0ACo=
DRM.card0.VGA.1:
 status: connected
 enabled: enabled
 dpms: Off
 modes: 1280x1024 1280x1024 1152x864 1024x768 1024x768 1024x768 832x624 800x600 800x600 800x600 800x600 640x480 640x480 640x480 640x480 720x400
 edid-base64: AP///////wBBDBHAgZQGACYPAQMfIht47h/1pFdHnSQTUFS/74CBgAEBAQEBAQEBAQEBAQEBMCoAmFEAKkAwcBMAUg4RAAAeAAAA/wAgQlogIDQzMTIzMwogAAAA/ABQaGlsaXBzIDE3MEMKAAAA/QA4TB5TDgAKICAgICAgAN8=
Date: Sun May 1 16:47:32 2011
DistUpgraded: Fresh install
DistroCodename: natty
DistroVariant: ubuntu
GdmLog2:

GraphicsCard:
 Intel Corporation Mobile 945GM/GMS, 943/940GML Express Integrated Graphics Controller [8086:27a2] (rev 03) (prog-if 00 [VGA controller])
   Subsystem: Toshiba America Info Systems Device [1179:ff10]
   Subsystem: Toshiba America Info Systems Device [1179:ff10]
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
InstallationMedia_: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
InstallationMedia__: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
MachineType: TOSHIBA Satellite A100
PccardctlIdent:
 Socket 0:
   no product info available
PccardctlStatus:
 Socket 0:
   no card
ProcEnviron:
 LANGUAGE=en_GB:en
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.38-8-generic root=UUID=6c8767b5-ce9c-421a-b6b8-03a6d20f50d8 ro quiet splash vt.handoff=7
ProcVersionSignature_: Ubuntu 2.6.38-8.42-generic 2.6.38.2
ProcVersionSignature__: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Renderer: Unknown
SourcePackage: unity
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 10/23/2006
dmi.bios.vendor: Phoenix Technologies LTD
dmi.bios.version: 2.10
dmi.board.name: MPAD-MSAE Customer Reference Boards
dmi.board.vendor: Intel Corporation
dmi.board.version: Not Applicable
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 1
dmi.chassis.vendor: No Enclosure
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnPhoenixTechnologiesLTD:bvr2.10:bd10/23/2006:svnTOSHIBA:pnSatelliteA100:pvrPSAA8E-17V049EN:rvnIntelCorporation:rnMPAD-MSAECustomerReferenceBoards:rvrNotApplicable:cvnNoEnclosure:ct1:cvrN/A:
dmi.product.name: Satellite A100
dmi.product.version: PSAA8E-17V049EN
dmi.sys.vendor: TOSHIBA
version.compiz: compiz 1:0.9.4+bzr20110415-0ubuntu2
version.libdrm2: libdrm2 2.4.23-1ubuntu6
version.libgl1-mesa-dri: libgl1-mesa-dri 7.10.2-0ubuntu2
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 7.10.2-0ubuntu2
version.xserver-xorg: xserver-xorg 1:7.6+4ubuntu3
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.14.0-0ubuntu4
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.14.0-4ubuntu7
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20110107+b795ca6e-0ubuntu7

[Colin Law (colin-law)]

On further investigation I see I was mistaken in thinking this is a Unity issue. I see the same symptom if I run the Classic desktop, with effects enabled, but do not see it if I run Classic desktop with effects disabled. Possibly it is a compiz issue.
I do not see the problem at all if I run in single monitor mode.

[Marco Biscaro (marcobiscaro2112)]

Probably a duplicate of bug #769650.