CPU load plasmoid not finding sensors (KDE, RPI4)

Hi, I’m experiencing an issue with the cpu-load plasmoids with the latest ARM stable release. Using KDE with RPI4. Plasmoids remain blank and there seem to be no sensor available. Ksysguard shows load and system information correctly, though. When the plasmoid are tested, ksystemstats jumps to 100% cpu usage and stays there for a while.

Unclear to me if:

  • this is an issue specific to RPI4
  • this is something that really emerged with the latest stable or I only failed to notice it before
  • this has to do with some ksystemstats transition where the sensors backend has been updated, and the plasmoids have not, introducing an API mismatch.

On most devices, plasmoids/widgets have no graphs, likely because the graphs require OpenGL higher than the GPU driver provides.

Is it just the graph that is missing or also the regular text information?

Everything is missing. Pressing the config button for the plasmoid shows “sensors” with no name. Trying to change that makes these unnamed sensors disappear and no other sensor seems to be available.
In addition to that the plasmoid does show the graph (scale, axes), only no curves are in there and the ordinate axis has a scale from zero to something times 10^-23. This does not look like an opengl issue. Furthermore the spike in cpu usage from ksystemstats is rather suspicious. In addition to that, even if this might not mean much, ksysguard seems to be able to provide very nice translucent graphs on the platform.

Unfortunately the fact that ksystemstats does not support any standard command line option (–help, or --version) and does not seem to offer any diagnostics is not very helpful in terms of understanding the root cause of the issue. I hope that the KDE devs can add that as ksystemstats mature.


While checking on another issue, I noticed these graphs do work on Arch ARM.
The one for Disks does not seem to work, but Memory and CPU do.

I have now opened a bug upstream (KDE bug 434922 — https://bugs.kde.org/show_bug.cgi?id=434922 — cannot link to it), but it would really be important to first find out if the issue is specific to ARM, specific to RPI4 within ARM, or specific to manjaro.

To the best of my understanding the issue seems to be with the ksystemstats daemon. This daemon is meant to be autostarted whenever there is something needing its services to look into system statistics (like CPU load). This is a relatively new daemon, so that currently plasma ships with some tools that rely on it (modern cpu load plasmoids) and tools that do not ksysguard…

On RPI4 manjaro stable, ksystemstats does not seem to work. It gets started correctly, but it fails to interact with its clients. This is why the clients cannot see any sensor nor display any data. At the same time ksystemstats locks into a situation that causes it to use 100% of the CPU.

@joe-77, I doubt this has to do with the lm_sensors up. I think that KDE has its own framework for accessing this kind of system information (the ksystemstats daemon).

@0n0w1c, can you please expand a little? On my system you can get the graphs correctly by using ksysguard (that does not appear to use ksystemstats yet) or older plasmoids (that do not use ksystemstats), but all the modern plasmoids (e.g., individual CPU load) fail and lead to a 100% resource usage from ksystemstats. What are you using to get the graphs?

As a side note… do people in the KDE plasma support forum see this, is the KDE label sufficient for that?

I was just testing and made an Arch Linux install for RPi4. I am not all that familiar with the inner workings of KDE. I noticed the “round” graphs in “System Monitor” work on Arch, where on my Manjaro install they remain blank.

Edit: plasma-systemmonitor-5.21.3-1 is the package.