Public bug reported:

Switching between apps was feeling extremely laggy and unsmooth after
some days of keeping the laptop on and just alt-tab-ing between apps
would keep the cpu consistently at 100% when hitting it more than 8-9
times per second and *not* letting go of Alt (meaning I stay at the same
app).

Also, just whizzing the mouse around on the screen (not moving anything)
would keep the cpu at 40-50%.

Some investigation (1) led me to try out restarting the gnome-shell
instance (killall followed by manually starting it in the terminal),
upon which everything seemed zippy again. No lagginess. The restart was
a supposed fix for a memory leak bug (2), but according to the comments
a bug fix was supposed to have landed in 18.04 long ago. So either this
has not been fixed or this bug is about something else - probably the
latter, as the reported memory usage in htop was nowhere near the
gigabytes of memory reported in the bug issue for 16722297.

Another thing worth mentioning perhaps, based on comments in (3) found
through (4), is that I have disabled all extensions. I used to use the
Coverflow extension.

Expected behaviour:
There should be no percieved lag or stuttering in the interface when switching 
between applications.

Actual behaviour:
Switching between applications causes a noticable lag/stuttering when the 
computer has been running for an extended period of time (weeks, but where it 
has mostly been suspended, meaning actual usage is limited to 3-4 days).


1. 
https://www.omgubuntu.co.uk/2018/03/gnome-shell-has-a-memory-leak-and-it-might-not-be-fixed-for-ubuntu-18-04-lts
2. https://bugs.launchpad.net/gnome-shell/+bug/1672297
3. https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1773959
4. https://askubuntu.com/a/1090987/165026

System info:
------------
Running Wayland.

Description:    Ubuntu 18.04.1 LTS
Release:        18.04

gnome-shell:
  Installert: 3.28.3-0ubuntu0.18.04.4
  Kandidat:   3.28.3-0ubuntu0.18.04.4
  Versjonstabell:
 *** 3.28.3-0ubuntu0.18.04.4 500
        500 http://no.archive.ubuntu.com/ubuntu bionic-updates/main amd64 
Packages
        100 /var/lib/dpkg/status
     3.28.1-0ubuntu2 500
        500 http://no.archive.ubuntu.com/ubuntu bionic/main amd64 Packages

** Affects: gnome-shell (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1817620

Title:
  High cpu usage on alt-tab-ing

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