[kde] [Bug 507456] New: KDE Powerdevil Performance Regression

[Mauro]

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-bugs at kde.org
          Reporter: calimauro at 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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