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mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,360

[SOLVED] plasma widget for 'Simple Monitor' has one cpu pegged at 100%

I have noticed after updating my systems that the plasma desktop 'Simple Monitor' that has always shown the cpu utilisation normally on all cores, has started showing one of the cpus pegged at 100% utilisation (it is cpu 3 on a laptop with 8 cpus threaded, and cpu 4 on a desktop which has 16 cpus threaded). On the other hand temperatures are normal, and htop shows all cpus operating at low cpu percentages ( <4%).  So it seems that an update to the plasma desktop presumably has a faulty Simple Monitor widget that is displaying anomalous utilisation on one core even though that core is running at low utilsation?  Has anyone else seen this?  If so is there a work around, or do we just have to wait until the widget gets updated?

Edit: I have reported at https://github.com/dhabyx/plasma-simple … /issues/61

Last edited by mcloaked (2023-07-24 14:38:20)

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Mike C

loqs

Member

Registered: 2014-03-06

Posts: 18,931

Re: [SOLVED] plasma widget for 'Simple Monitor' has one cpu pegged at 100%

https://bbs.archlinux.org/viewtopic.php?id=287343 ?

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,360

Re: [SOLVED] plasma widget for 'Simple Monitor' has one cpu pegged at 100%

Thanks loqs - and reading through the linked thread - I found that killing mysqld stops the rogue core being at 100% and it then looks fine - and seems related to akonadi in my case.

Edit: I added more comments to the linked thread - it wasn't actually fine and displaying differently using mpstat still shows a rogue core.

Last edited by mcloaked (2023-07-22 21:27:58)

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Mike C

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,360

Re: [SOLVED] plasma widget for 'Simple Monitor' has one cpu pegged at 100%

I downgraded the kernel back to 6.4.3 and the issue is no longer present - so it is clearly a bug in kernel 6.4.4

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Mike C

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,360

Re: [SOLVED] plasma widget for 'Simple Monitor' has one cpu pegged at 100%

There have been ongoing posts in the LKML and the net conclusion is that the kernel is doing the right thing with the commit that was suggested underlies this observation. So using the current kernel that includes the commit does generate a display of 100% usage on one core, when mysql is running, in the plasma widget Simple Monitor. However that display is apparently anomalous, and in reality that core is using high io-wait percentage, and not actually in use 100% of the time. In my case it is when logged in to the Plasma Desktop, that akonadi is running (even though I don't have any programs that need it).  So I can execute 'akonadictl stop' which then shuts down mysqld, and the cpu monitor display no longer shows one core using 100% cpu (incorrectly).

So the problem seems to be the system monitor widget in my case showing incorrect high cpu usage on any core that is using high io-wait.  In addition I would very much like to not have akonadi running at all, but there seems no obvious way to prevent it running when I log in to the plasma desktop.  In addition I note that akonadi is calling the mysqlcheck in an obsolete way, since there is a journal entry:

Jul 24 09:29:38 lenovo2 kalendarac[1236]: /usr/bin/mysqlcheck: Deprecated program name. It will be removed in a future release, use '/usr/bin/mariadb-check' instead

from the kalendarac - and it would be nice to not have kalendarac started since I don't need it - but I can't find a way to prevent that from starting during plasma startup. Does anyone know how to prevent it starting?

Last edited by mcloaked (2023-07-24 09:59:41)

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Mike C

loqs

Member

Registered: 2014-03-06

Posts: 18,931

Re: [SOLVED] plasma widget for 'Simple Monitor' has one cpu pegged at 100%

Have you looked at https://unix.stackexchange.com/question … at-startup

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,360

Re: [SOLVED] plasma widget for 'Simple Monitor' has one cpu pegged at 100%

Yes, loqs, I did and that led me to further search and found:

cp /etc/xdg/autostart/org.kde.kalendarac.desktop ~/.config/autostart

edit the file and change:
X-KDE-autostart-condition=kalendaracrc:General:Autostart:true
to
X-KDE-autostart-condition=kalendaracrc:General:Autostart:false

which I will tinker with and see if that leads to mysql not being started by akonadi - or not... there must be a good solution!

Edit: Well, that stopped kalendarac autostarting, but there is something else that starts akonadi.  I thought it might be kclockd but it is not clear if that needs to be running or not.  Either way, even though kalendarac is not started I still need to do akonadictl stop to shut down mariadb. I can stop kclockd but akonadi, and mariadb are still running unless I manually close them.

Last edited by mcloaked (2023-07-24 13:40:21)

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Mike C

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,360

Re: [SOLVED] plasma widget for 'Simple Monitor' has one cpu pegged at 100%

I finally found the solution that works. 

Edit ~/.config/akonadi/akonadiserverrc

Change last line to
StartServer=false

Now mysqld is not running after logging in to the plasma desktop and 'akonadictl status' shows the akonadi server is stopped. In addition checking there are no processes running for akonadi or mysql/mariadb shows that all is now well.

Last edited by mcloaked (2023-07-24 14:48:15)

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Mike C

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,360

Re: [SOLVED] plasma widget for 'Simple Monitor' has one cpu pegged at 100%

Tested kernel 6.4.6 built with the referenced patch  [1] , from the kernel bugzilla, and the anomalous 100% cpu activity on a single core is no longer displayed in the System Monitor widget, and mpstat no longer shows >94% io-wait. So this resolves the issue for my systems.

[1] https://lore.kernel.org/lkml/11ded843-a … nel.dk/raw

Last edited by mcloaked (2023-07-24 18:42:55)

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Mike C