https://bugs.kde.org/show_bug.cgi?id=526595
Bug ID: 526595
Summary: changing Sensor.sensorId does not unsubscribe the
previous sensor
Classification: Frameworks and Libraries
Product: ksystemstats
Version First 6.7.5
Reported In:
Platform: NixOS
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: General
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
Created attachment 196793
--> https://bugs.kde.org/attachment.cgi?id=196793&action=edit
QML reproducer; run with "-- clear-id": sets sensorId to "" after 5 s
DESCRIPTION
Changing the sensorId of a Sensor (for example setting it to "") does not
unsubscribe the previous sensor, so it stays subscribed for the lifetime of the
process. On an NVIDIA laptop this keeps `nvidia-smi dmon` running and the dGPU
never runtime-suspends.
STEPS TO REPRODUCE
1. On a system with an NVIDIA GPU, make sure nothing else uses gpu/gpu0 sensors
(no nvidia-smi process running).
2. Run the attached libksysguard-stale-subscriptions.qml with `qml
libksysguard-stale-subscriptions.qml -- clear-id`. It creates a Sensor for
gpu/gpu0/usage and sets its sensorId to "" after 5 seconds.
3. Watch for the `nvidia-smi dmon` process started by ksystemstats.
OBSERVED RESULT
nvidia-smi dmon keeps running after sensorId is cleared. It stops only when the
qml process exits.
EXPECTED RESULT
The old sensor is unsubscribed when sensorId changes, so nvidia-smi dmon stops.
SOFTWARE/OS VERSIONS
Operating System: NixOS 26.11
KDE Plasma Version: 6.7.5
KDE Frameworks Version: 6.30.0
Qt Version: 6.11.2
Kernel Version: 7.2.8 (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 260 w/ Radeon 780M Graphics
Memory: 24 GiB of RAM (22.8 GiB usable)
Graphics Processor 1: AMD Radeon 780M Graphics
Graphics Processor 2: NVIDIA GeForce RTX 5050 Laptop GPU
libksysguard / ksystemstats: 6.7.5
NVIDIA driver: 615.71.09 (open kernel module), PRIME offload with runtime D3
power management
ADDITIONAL INFORMATION
Filed under ksystemstats because I could not find a libksysguard product.
Sensor::setSensorId() in sensors/Sensor.cpp subscribes to the new id but never
unsubscribes from the old one. Only disabling the Sensor or destroying it
unsubscribes. Same code on master.
QML code that stops using a sensor by clearing or changing sensorId leaks the
subscription for the lifetime of the process. I found this through the SysPeek
plasmoid, which scans gpu/gpu0..gpu8 this way at startup and kept the NVIDIA
dGPU awake (nvidia-smi running, no D3cold, about 7 W extra on battery).
Related: bug 497024.
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