https://bugs.kde.org/show_bug.cgi?id=507456
Bug ID: 507456
Summary: KDE Powerdevil Performance Regression
Classification: I don't know
Product: kde
Version First unspecified
Reported In:
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: unassigned-b...@kde.org
Reporter: calima...@yahoo.com
Target Milestone: ---
SUMMARY
STEPS TO REPRODUCE
1. Login to your account
2. Experience super slow login
3. After looking in the logs what's the issue, powerdevil seems to take long
time to start due to timeout with dccutil execution
OBSERVED RESULT
Login after password successful takes around 15seconds to get to the fully
functional desktop
Result of the command $ time systemctl --user restart plasma-powerdevil.service
real 0m12,568s
user 0m0,000s
sys 0m0,004s
EXPECTED RESULT
Login in 2 seconds
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Kubuntu 25.04
KDE Plasma Version: 6.3.4
KDE Frameworks Version: 6.12.0
Qt Version: 6.8.3
ADDITIONAL INFORMATION
Summary
KDE Powerdevil service takes 13+ seconds to start instead of <1 second, causing
significant login delays after a recent libddcutil upgrade in Kubuntu 25.04.
Environment
OS: Kubuntu 25.04 (Plucky Pufferfish)
KDE Plasma: 6.3.4
Powerdevil: 4:6.3.4-0ubuntu1
libddcutil: 2.2.0-1 (upgraded from libddcutil4 1.4.1-1build2)
Hardware: AMD Ryzen 9 5900X, AMD RX 6700 XT (16GB VRAM)
Monitors: 2x ASUS ROG displays via DisplayPort
ASUS ROG PG278QR (2016, Week 43)
ASUS ROG PG279Q (2016, Week 2)
Timeline of Issue
October 7, 2024: Initial installation with libddcutil4 1.4.1 - working normally
July 6, 2025: libddcutil4 removed during system update - problems began
July 22, 2025: Investigation revealed the regression
Problem Description
After the July 6, 2025 update that removed libddcutil4 and later installation
of libddcutil5 2.2.0-1, powerdevil consistently takes 13+ seconds to
initialize, causing significant delays during login.
Root Cause Analysis
Powerdevil service logs show libddcutil spending excessive time communicating
with monitors via DDC/CI:
jui 22 08:20:53 mauro-amd org_kde_powerdevil[2723]: Starting libddcutil.
library built Feb 22 2025 at 15:37:45
jui 22 08:20:53 mauro-amd org_kde_powerdevil[2723]: Initializing libddcutil.
ddcutil version: 2.2.0-dev
jui 22 08:20:55 mauro-amd org_kde_powerdevil[2723]: busno=9, sleep-multiplier=
2,00, Testing for unsupported feature 0xdd returned Error_Info[DDCRC_RETRIES
jui 22 08:20:55 mauro-amd org_kde_powerdevil[2723]: Turning off dynamic sleep
and retrying
jui 22 08:20:56 mauro-amd org_kde_powerdevil[2723]: busno=9, sleep-multiplier =
1,00, Retesting for unsupported feature 0xdd
[...pattern repeats for ~13 seconds across bus 9 and 10...]
jui 22 08:21:06 mauro-amd org_kde_powerdevil[2723]: Library initialization
complete.
Performance Comparison
DDC/CI detection times:
HDMI connection: 1.6 seconds (normal)
DisplayPort connection: 6.7+ seconds (problematic)
Manual ddcutil testing:
$ ddcutil detect --sleep-multiplier 0.3 --disable-dynamic-sleep
Display 1
I2C bus: /dev/i2c-9
DRM connector: card1-DP-1
Model: ROG PG278QR
[Completes in ~3 seconds]
Display 2
I2C bus: /dev/i2c-10
DRM connector: card1-DP-2
Model: ROG PG279Q
[Completes in ~3 seconds]
System Logs Evidence
Package change history:
$ grep "ddcutil" /var/log/dpkg.log*
/var/log/dpkg.log:2025-07-06 09:10:36 remove libddcutil4:amd64 1.4.1-1build2
<none>
/var/log/dpkg.log:2025-07-06 09:10:36 status not-installed libddcutil4:amd64
<none>
/var/log/dpkg.log:2025-07-22 09:55:26 install ddcutil:amd64 <none> 2.2.0-1
Current package versions:
$ dpkg -l | grep -E "(ddcutil|powerdevil)"
ii ddcutil 2.2.0-1 amd64 Control
monitor settings
ii libddcutil5:amd64 2.2.0-1 amd64 Control
monitor settings - shared library
ii libpowerdevilcore2:amd64 4:6.3.4-0ubuntu1 amd64 shared
library for KDE power management
ii powerdevil 4:6.3.4-0ubuntu1 amd64 KDE power
management service for Plasma
I/O errors in system logs:
jui 22 10:35:17 mauro-amd fwupd[7971]: failed to add device
card1-DP-1/drm_dp_aux0: failed to read device firmware header: failed to write
7 bytes to 14: Erreur d'entree/sortie
jui 22 10:35:17 mauro-amd fwupd[7971]: failed to add device
card1-DP-2/drm_dp_aux1: failed to read device firmware header: failed to write
7 bytes to 14: Erreur d'entree/sortie
Analysis and Evidence
Hardware is not the issue: Identical symptoms appearing simultaneously on two
different monitor models with different manufacturing dates is statistically
improbable
DisplayPort vs HDMI: DDC/CI works significantly faster on HDMI than DisplayPort
for the same monitors
Regression timing: Problem correlates precisely with libddcutil4 → libddcutil5
upgrade
Version evidence: libddcutil5 2.2.0-1 is a development version (2.2.0-dev) with
apparent regressions
Attempted Solutions
The following configuration attempts had no effect on powerdevil startup time:
Environment variables: POWERDEVIL_NO_DDC=1, DDCUTIL_SLEEP_MULTIPLIER=0.3
ddcutil configuration files: /etc/ddcutil/ddcutilrc with optimized parameters
Systemd service overrides: Custom environment variables in service
configuration
Wrapper scripts: Custom powerdevil executable wrapper with environment settings
Reproduction Steps
Install Kubuntu 25.04 with libddcutil5 2.2.0-1
Connect multiple DisplayPort monitors (eventually older models from 2016-2017)
Observe powerdevil startup time: time systemctl --user restart
plasma-powerdevil.service
Compare with HDMI connection on same monitors
Significant user experience degradation during login (13+ second delays)
No workaround available through configuration
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