Comment # 9 on bug 999738 from Wolfgang Bauer

(In reply to Dr. Werner Fink from comment #8)
> What is going on on this bug entry ... I'd like to have a solution. How to
> avoid this nasty polling loop?

Sorry, busy with other stuff...

For a "solution", we'd need to find out what exactly is causing it though and
that may not be easy.

Some comments:
(In reply to Dr. Werner Fink from comment #2)
> To reproduce this the user has to have to lock his screen within KDE
> plasmashell. And the account of the user is not an fresh KDE but an older

It doesn't happen here.

Is the desktop still usable when the CPU usage goes high, or is the desktop
frozen?
Or does it only happen while the screen is locked?

> This does not happen with other session managers from other users.

With "session managers" you mean other desktop environments than Plasma5?
As it's plasmashell that takes the CPU, that's to be expected I suppose.

Can you try if it happens on a fresh user account too, please?
Would at least show whether this happens with the default setup as well, or is
caused by something extra.

(In reply to Dr. Werner Fink from comment #5)
> Created attachment 693197 [details]
> strace -f from tracker-miner-apps

(In reply to Dr. Werner Fink from comment #6)
> Created attachment 693198 [details]
> strace -f tracker-store

Tracker is GNOME's file indexer and unrelated to KDE/Plasma.
You probably should not even have it installed when using Plasma5, KDE has its
own (baloo), and you probably have both running which of course can also drain
your CPU.

I would suggest to uninstall it or remove KDE from the "OnlyShowIn" line in
tracker's autostart .desktop file (in /etc/xdg/autostart/), but I don't really
think it would cause your Plasma problem.

(In reply to Dr. Werner Fink from comment #4)
> Created attachment 693196 [details]
> strace -f from plasamshell

I see many references to PulseAudio in there.
Can you try to disable PulseAudio as a test?
YaST->Hardware->Sound->Other->PulseAudio Configuration

And/or disable the volume control in the "System Tray Settings".

(In reply to Dr. Werner Fink from comment #7)
> Hmm ... sending SIGSEGV causes a new peocess

Yes, plasmashell gets restarted automatically if it crashes.
This is by design.

Googling for your problem, I found this:
https://bugs.launchpad.net/ubuntu/+source/plasma-workspace/+bug/1435641
That's an older bug report, it seemed to have been caused by the IM applet, so
try to disable that one too if you use it.

The last comment (probably unrelated to the original report) states that it
happens when connecting/disconnecting to/from a docking station or after
hibernating.

And https://forum.kde.org/viewtopic.php?f=289&t=121533&start=45 indicates a
similar problem when using skype (which may relate to PulseAudio too).
Are you using skype? Does it happen too when skype is not running?

Also, we added a patch recently (to the 5.8 packages) that should fix a high
CPU usage problem in plasmashell.
https://build.opensuse.org/package/view_file/KDE:Frameworks5:LTS/plasma5-workspace/add-tray-icon-cache.patch?expand=1

Unfortunately backporting it to 5.5 will not be possible because the system
tray has been rewritten from scratch in 5.8 (though the question is if that
particular problem even existed in 5.5).

You could try to remove the system tray completely though as a test (click on
toolbox icon on the right edge to open the toolbox, then right-click on the
system tray, there should be a "Remove" option then).

Another possible option would be to try upgrading to 42.2 beta, which has the
latest Plasma and much newer Qt5 packages (5.8 and 5.6.1 respectively).