gnome-shell very high %CPU usage while moving mouse on Ubuntu 20.04

[Pavils Jurjans]

After upgrade from 18.04 to 20.04 I discovered that gnome-shell occasionally starts eating up unreasonably large CPU %. After some head scratching why on earth i thappens, it was clear that moving my mouse energetically I can get it as close to 100% as I want.

If this is relevant, the mouse model is Corsair Harpoon wireless BT. I am reading some speculation that the cause of the problem is high polling rate for mouse location (?).

It is suggested in this bug entry (https://bugs.launchpad.net/bugs/1848951) that this issue is fixed on late march. But this is october and I still experience this problem on an updated PC.

gnome-shell version on my system: 3.36.4-1ubuntu1~20.04.2
---
ProblemType: Bug
ApportVersion: 2.20.11-0ubuntu27.9
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
DisplayManager: gdm3
DistroRelease: Ubuntu 20.04
InstallationDate: Installed on 2018-08-18 (794 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
NonfreeKernelModules: lkp_Ubuntu_5_4_0_48_52_generic_72 nvidia_modeset nvidia
Package: gnome-shell 3.36.4-1ubuntu1~20.04.2
PackageArchitecture: amd64
ProcVersionSignature: Ubuntu 5.4.0-48.52-generic 5.4.60
RelatedPackageVersions: mutter-common 3.36.6-1ubuntu0.20.04.2
Tags: focal
Uname: Linux 5.4.0-48-generic x86_64
UpgradeStatus: Upgraded to focal on 2020-10-04 (16 days ago)
UserGroups: adm cdrom dialout dip docker kvm lpadmin plugdev sambashare sudo vboxusers
_MarkForUpload: True

[Daniel van Vugt (vanvugt)]

1. Bugs like this are usually due to extensions. So first please try disabling any extensions.

2. Please run this command to send us more information about the system:

   apport-collect 1900760

3. I have actually seen one possible cause for this in recent code changes, but it would only happen after locking and unlocking the machine. Is that what you find?.. https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1459 is fixed in gnome-shell 3.38.2.

[Pavils Jurjans (passiday)]

apport information

[Pavils Jurjans (passiday)]

apport information

[Pavils Jurjans (passiday)]

apport information

[Pavils Jurjans (passiday)]

apport information

[Pavils Jurjans (passiday)]

apport information

[Pavils Jurjans (passiday)]

apport information

[Pavils Jurjans (passiday)]

Whoa, there's a lot of info in those apport files. I hope those are relevant.

I don't use any fancy Gnome shell extensions. Here's an output of `ls /usr/share/gnome-shell/extensions/`:

desktop-icons@csoriano <email address hidden> <email address hidden>

That's about it.

It's hard to tell right now if the problem surfaces only after locking/unlocking routine. I can confirm that when I was submitting this bug report, the system has indeed went through several sleep and wake-up cycles, and, of course, there was a lock screen every time a wake-up happened.

[Daniel van Vugt (vanvugt)]

Thanks for all that.

It appears the main CPU hog here is bug 1849142, which has a fix coming soon. So to exclude that bug and see if it is the main problem, please:

 1. Open the Extensions app

 2. Disable 'Ubuntu AppIndicators'

 3. Reboot.

 4. If the problem happens after that then please again run:

    apport-collect 1900760

[Pavils Jurjans (passiday)]

Did that, now it's much better. Although I was deferring from system updates, reluctant to restart, so this was not a clean test.

Moving mouse quickly still makes the Xorg process consume signifficant CPU% (up to 25%), but gnome-shell doesn't get near to the level it used to consume.

It's a weird combo, a bug related to Discord app and mouse movement processing, causing the said CPU hog.

Thanks for the fix, I guess.

[Daniel van Vugt (vanvugt)]

OK let's call this a duplicate of bug 1849142. Yes it is weird that would be mouse-related...

Bug 1848951 is still open to cover the high CPU in Xorg.