On my Raspbian 2018-11-13 installation with all updates (`sudo apt-get update` and `sudo apt-get upgrade`), I see the CPU graph in the task bar (top right corner) at constant 25%.

I opened a terminal and used `top` to have a look at the process list and CPU consumption. It tells me that `lxpanel` is at 100% CPU, which AFAIK matches the 25% of the graph, since my RPi3 has 4 cores and `top` uses 100% for one core, whereas the graph will be filled 25% only (100% of 400%).

There are already a lot of Google results for this issue, dating back until 2011. It seems to apply to various operating systems, including Debian, Ubuntu and LXDE.

I've also seen a [similar question](https://raspberrypi.stackexchange.com/questions/27596/lxterminal-pegs-my-cpu-at-100) here on this site, but it lacks detailed information, blames `lxterminal` and the answer is not helpful.

I'd like to know:

* what may cause this issue?
* how to mitigate this issue?
* how to provide useful information for lxpanel developers? (e.g. call stacks during the 100% CPU usage)

I've not yet figured out on how to reproduce this issue. It seems that it's related to working with lxpanel. IMHO I saw it happen after pairing Bluetooth, connecting to WLAN and operating with USB Sticks. However, I can't provide a sequence of steps yet. Every time I try to reproduce it, it fools me.

However, I hope that this problem can be reproduced and solved now, since it happens on a standardized platform, compared to the various different installations I googled about.

Things I've tried:

* rebooting. This usually helps for a while until the issue reappears. Obviously, rebooting every now and then is not an acceptable solution.
* killing `lxpanel` and starting it again. This helps, but the panel has a different look and feel.
* [Github Linux Issue 2518](https://github.com/raspberrypi/linux/issues/2518), but it was closed as not reproducible. They talk much about power issues. I am using a 6 Amp lab power supply.
* a [topic in the RPi forum](https://www.raspberrypi.org/forums/viewtopic.php?t=121022) where they suggest to disable the CPU panel. Actually I don't want to disable it. It's useful, since I am developing software and I want to see whether there could be a performance issue in my code (like I spotted the 25% of lxpanel).
* a short and not helpful post in [LXDE forums](https://forum.lxde.org/viewtopic.php?t=3117) from 2011
* [Debian bug 669242](https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=669242), which should be fixed since 2013
* a [forum post on LXLE](http://www.lxle.net/forums/discussion/344/lxpanel-eating-cpu/p1) running from a Live DVD (2014).
* an [Ubuntu Forum post](https://ubuntuforums.org/showthread.php?t=1915238) suggesting to switch the OS completely

As you can see, all findings seem to miss a root cause analysis. If I can't solve it, I'd like to participate in such a root cause analysis, since it happens quite often on my machine.

Things that might be special in my configuration, although I can't see a relationship to lxpanel:

* I have SPI enabled
* I have the internal sound card disabled via `/boot/config.txt`
* I have set the USB sound card as the default sound card in `/usr/share/alsa/alsa.conf`