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[Bug 1744515] [NEW] Compiz flashback has high-CPU kworker thread when screen updates


Public bug reported:

When the screen updates, there is one or two kworker threads with high
CPU. This is 30~40% of a CPU as shown in top, on my old system with two
CPU cores.

This did not happen in 16.10. I recently upgraded a badly out-of-date
16.10 to 17.04 and then immediately to 17.10, so I don't know when it
showed up.

Examples of when it happens is when a video player like ffplay is
running, even if it's just showing something very simple like the sound
frequencies in a music file, or when I scroll up and down in this
browser window. The size of the window is unimportant; the same kworker
activity is shown whether the window is maximized or reduced to a small
width and zero height. It goes away if the window is minimized.

It doesn't happen in Metacity flashback, in "Ubuntu with Xorg", or with
"Gnome with Xorg" from the login screen. For some reason I have
duplicates of those last two options, that differ in that one of them
has a blank circle for the icon. What are presumably the Wayland options
don't let me login — if I try to select them, there's a white outline
and the previous option stays selected with a filled background, and the
selection menu stays there until I select an Xorg-based option. So I
can't test those. '"Ubuntu with Xorg" and "Gnome with Xorg" did show
gnome-shell with ~15% CPU usage of a core, which is probably unnecessary
but completely unrelated to this bug.

Metacity flashback in 17.10 showed the CPU usages I experienced in 16.10
with Compiz flashback, which is about 10% of total CPU from user and
system while playing an audio file with frequency display in ffplay.
This bug brings system CPU as shown in 'top' to 25%.

If it helps, the active kworker thread seems to always be named
'kworker/u4:number', usually the same one or two threads.

I tried enabling or disabling some compiz options related to screen
drawing, but it didn't seem to do anything. I didn't disable the
'Composite' or 'OpenGL' plugins as they were required by too many

This is filed under compiz because no other window manager leads to the
problem, even though it isn't the compiz process with high CPU.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: compiz 1:
ProcVersionSignature: Ubuntu 4.13.0-21.24-generic 4.13.13
Uname: Linux 4.13.0-21-generic x86_64
ApportVersion: 2.20.7-0ubuntu3.7
Architecture: amd64
CompizPlugins: [core,composite,opengl,compiztoolbox,decor,imgpng,regex,gnomecompat,place,move,vpswitch,mousepoll,obs,wall,animation,shift,snap,resize,expo,session,ezoom,workarounds,staticswitcher,fade]
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: GNOME-Flashback:GNOME
Date: Sat Jan 20 16:04:52 2018
DistUpgraded: 2018-01-08 23:06:14,204 DEBUG Running PostInstallScript: './xorg_fix_proprietary.py'
DistroCodename: artful
DistroVariant: ubuntu
 NVIDIA Corporation G96M [GeForce 9650M GT] [10de:064c] (rev a1) (prog-if 00 [VGA controller])
   Subsystem: ASUSTeK Computer Inc. G96M [GeForce 9650M GT] [1043:1912]
 b'org.compiz.core' b'outputs' b"['1024x768+0+0', '1024x768+0+0']"
 b'org.compiz.core' b'hsize' b'2'
 b'org.compiz.core' b'active-plugins' b"['core', 'composite', 'opengl', 'compiztoolbox', 'showrepaint', 'imgjpeg', 'decor', 'imgpng', 'regex', 'gnomecompat', 'place', 'move', 'mousepoll', 'obs', 'ezoom', 'workarounds', 'dbus', 'text', 'wall', 'snap', 'resize', 'staticswitcher', 'session', 'fade', 'bench']"
 b'org.compiz.core' b'vsize' b'2'
 b'org.compiz.core' b'lower-window-button' b"'Disabled'"
MachineType: ASUSTeK Computer Inc. N50Vn
PackageArchitecture: all
ProcKernelCmdLine: root=UUID=b09dc720-93ec-4fdf-a42f-7ea19a9af555 ro quiet splash
SourcePackage: compiz
UpgradeStatus: Upgraded to artful on 2018-01-09 (11 days ago)
dmi.bios.date: 03/05/2009
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 211
dmi.board.asset.tag: ATN12345678901234567
dmi.board.name: N50Vn
dmi.board.vendor: ASUSTeK Computer Inc.
dmi.board.version: 1.0
dmi.chassis.asset.tag: ATN12345678901234567
dmi.chassis.type: 10
dmi.chassis.vendor: ASUSTeK Computer Inc.
dmi.chassis.version: 1.0
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr211:bd03/05/2009:svnASUSTeKComputerInc.:pnN50Vn:pvr1.0:rvnASUSTeKComputerInc.:rnN50Vn:rvr1.0:cvnASUSTeKComputerInc.:ct10:cvr1.0:
dmi.product.name: N50Vn
dmi.product.version: 1.0
dmi.sys.vendor: ASUSTeK Computer Inc.
version.compiz: compiz 1:
version.libdrm2: libdrm2 2.4.83-1
version.libgl1-mesa-dri: libgl1-mesa-dri 17.2.4-0ubuntu1~17.10.2
version.libgl1-mesa-glx: libgl1-mesa-glx 17.2.4-0ubuntu1~17.10.2
version.xserver-xorg-core: xserver-xorg-core 2:1.19.5-0ubuntu2
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.10.5-1ubuntu1
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.10.0-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20170309-0ubuntu1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.15-2
xserver.bootTime: Sat Jan 20 15:45:37 2018
xserver.configfile: default
 Failed to load module "nvidia" (module does not exist, 0)
 Failed to load module "nvidia" (module does not exist, 0)
xserver.logfile: /var/log/Xorg.0.log
xserver.version: 2:1.19.5-0ubuntu2
xserver.video_driver: nouveau

** Affects: compiz (Ubuntu)
     Importance: Undecided
         Status: New

** Tags: amd64 apport-bug artful compiz-0.9 ubuntu

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  Compiz flashback has high-CPU kworker thread when screen updates

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