Public bug reported:
Bugg report made after many tryings, assisted with AI. AI prepared the
text below.
lsb_release -rd
Description: Ubuntu 26.04 LTS
Release: 26.04
Expect a system working fine
What append below ...
What I can report by myself :
- Processor began warming too much before upgrade to kubuntu 26.10. and
computer feeze
- process plasmashell, and kwin_wayland too high (it always change in htop
between 20 and 40% each)
- trying precedents kernels No change
- trying new users No change
- trying kubuntu 26.06 live USB It's fine
- Updating my installation.... it seems to be better, since I lanche Dolphin,
then Process Dolphin and kwin_wayland too high
- new user does not give better results
Maybe some config or softwares that where keept from my precedent
install. Maybe something to debug my wifi. I tried to understand all
what IA proposed me but cannot wrap or resume ...
That's what I can say ...
----
Summary: On a Dell Latitude 7400 (Intel UHD Graphics 620), a fresh installation
of Kubuntu 26.04 results in immediate exessive CPU usage on kwin_wayland
(arround 40%) and plasmashell (arround 60%) upon user login (on 8 processors
system, then it becomes too warm). The system becomes sluggish, and graphical
tools freeze.
CRITICAL: The Live USB of Kubuntu 26.04, running the exact same kernel
(7.0.0-14) on the exact same hardware, works perfectly with normal CPU
usage (<15%).
System Configuration (Installed - Buggy):
OS: Kubuntu 26.04
Kernel: 7.0.0-14-generic
Mesa: 26.0.3-1ubuntu1
KDE Plasma: 6.6.4
GPU: Intel WhiskeyLake-U GT2 [UHD Graphics 620]
Driver: i915 (kernel module)
Troubleshooting Steps Performed (All Negative):
New User: Issue persists on a brand new user account (no config files).
Obsolete Packages: Cleaned all orphaned/old packages (autoremove, check).
No change.
Custom Scripts: Removed all custom scripts from
/etc/xdg/Xwayland-session.d/. No change.
SDDM Config: Verified standard SDDM configuration files. No custom
overrides found.
Kernel Parameters: Tested with/without i915.enable_dc=0. No change.
Comparison: Live USB (Kernel 7.0.0-14) is stable. Installed system (Kernel
7.0.0-14) is unstable.
Hypothesis:
A config in wifi module done some weeks before update that still introduce
problems.
WiFi Driver: Tested with iwlwifi module disabled/config removed. No change,
to be tested again, not so shure. Give commands please.
There is a binary divergence or file corruption in the installed
system's libraries (likely Mesa, KWin, or Qt dependencies in /usr/lib)
compared to the Live USB image. The installed packages report the same
version numbers (apt policy), but the behavior suggests a mismatch or
corruption specific to the disk installation process or upgrade path.
Impact: Desktop environment is unusable on Wayland with Intel UHD 620 on
fresh Kubuntu 26.04 installations. Users are forced to use alternative
file managers (e.g., Krusader).
Logs: journalctl shows repeated i915 atomic update failures when the
loop occurs, but these also appear occasionally on the working Live USB
without causing freezes, suggesting a threshold or timing issue specific
to the installed binary set.
** Affects: kwin (Ubuntu)
Importance: Undecided
Status: New
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Bugs, which is subscribed to kwin in Ubuntu.
https://bugs.launchpad.net/bugs/2150766
Title:
[Kubuntu 26.04 / Kernel 7.0.0-14] Critical CPU loop in
kwin_wayland/plasmashell on login (Intel UHD 620). Works perfectly on
Live USB with same kernel.
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