How to determine why Core 2 of 8 has CPU usage 100% constantly?

[Gary1]

Hello, Would you please provide some direction on how to go about determining what is using CPU when no applications are open except System Monitor?

I noticed that the CPU was jumping between 13% and 20% with no apps. open and tried looking at processes and tried looking using Htop but that was equllay challenging for me. I shutdown/rebooted twice with no change.

Anyway, I stumbled across the part of System Monitor that shows usage by core. I have an HP Elitedesk with 8 cores and noticed that core 2 shows 100% constantly.

How can I figure out what that means, such as is core 2 being used or damaged?

I’m pretty sure that CPU usage is usually very low on my machine (as I use it, anyway) because sometimes I watch it when doing what, for me, are complicated data reads, manipulation, and writes to SQLite databases that last for a couple hours and CPU usage remains at about 15% throughout.

Thank you for any guidance you may be able to provide.

EDIT:
I think I figured it out. I have a LAMP stack on the machine but haven’t used it in several months. It appears that for some reason, HTTPD and MariaDB were started again at startup and were using 100% of Core 2. After trying systemctl stop mariadb and systemctl stop httpd, Core 2 went to 0%; and total CPU jumps around from 0.5 to 4% again.

When looking at the CPU usage by process, neither of these showed a value for CPU usage though. Why, when a core is at 100%, does the process list not show a value?

I started httpd and mariadb, again, to see what would happen and Core 5 goes to 100%; but when I look in System Montior by process and see them listed, the CPU value for both is blank.

Thank you.

[cscs]

Probably the same as the reported-in-12-other-threads issue of mariadb+akonadi

[Stable Update] 2023-07-27 - Kernels, Nvidia, Virtualbox, Thunderbird, LibreOffice, Pipewire

Its triggered by akonadi (used by Kalendar) … but mariadb is the culprit. The kernel is doing what it should … reporting had changed slightly. That said a proposed kernel patch circumvents the issue by narrowing the reports and squashing another unrelated bug. https://lore.kernel.org/lkml/11ded843-ac08-2306-ad0f-586978d038b1@kernel.dk/

Akonadi causes high CPU load

Good evening. This is a known reported bug with akonadi+mariadb ( most often triggered in these forums by ‘Kalendar’ ) (( and not the same as @Aragorn, we thinks, as aragorn is privvy to that bug ))

[Unstable Update] 2023-05-21 - Repository changes

Last post on the thread indicates its a mariadb issue (being leveraged by akonadi because of Kalendar) I found the process that was using a lot of IO-Wait to the CPU. It was MariaDB (11.0.2). I use Kalendar as my Calendar program since i use KDE Plasma and this program uses Akonadi which uses MariaDB to store data on it. Can you confirm this ? PS. I leave this here for those who may wish to try a different DB with Akonadi: https://wiki.archlinux.org/title/KDE#Akonadi

(its also just cosmetic)

[Gary1]

Thank you for the response.

I assume it must be related since stopping mariadb and httpd resolved it. However, I don’t have akonadi installed; don’t recall why I got rid of it but did quite some time ago.

pactree -r akonadi 
error: package 'akonadi' not found

I also don’t have Kmail or Kalendar installed.

Running kernel 5.15 but have 6.1.44-1 installed.

Thanks.

[cscs]

While I believe the only examples I saw were it being caused by akonadi … it was technically an issue between mariadb and the kernel … so I suppose it happening without it is entirely plausible.

[MrLavender]

Yeah, it’s mariadb. I don’t use akonadi either but I do have mariadb running all day for work and I see it.

It’s just a cosmetic issue, ignore it. It’s already been fixed in htop and many other tools but not in KDE System Monitor which still shows one core pegged at 100%.