https://bugs.kde.org/show_bug.cgi?id=526594
Bug ID: 526594
Summary: Sensor stays subscribed when one client subscribes to
it twice and then unsubscribes twice
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 196792
--> https://bugs.kde.org/attachment.cgi?id=196792&action=edit
QML reproducer: two Sensors for gpu/gpu0/usage in one process, destroyed after
5 s
DESCRIPTION
When one client subscribes to the same sensor twice and later unsubscribes
twice, ksystemstats keeps the sensor subscribed until the client disconnects.
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 ksystemstats-duplicate-subscribe.qml with `qml`. It creates
two Sensor objects for gpu/gpu0/usage in one process and destroys both after 5
seconds.
3. Watch for the `nvidia-smi dmon` process started by ksystemstats.
OBSERVED RESULT
nvidia-smi dmon starts when the sensors are created and keeps running after
both Sensor objects are destroyed. It stops only when the qml process exits.
EXPECTED RESULT
nvidia-smi dmon stops once no Sensor uses gpu/gpu0/usage anymore.
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
libksysguard sends a separate subscribe call for every Sensor object, so a
single client (for example plasmashell with two widgets showing the same
sensor) can subscribe the same path twice.
In src/client.cpp, Client::subscribeSensors() calls sensor->subscribe() every
time, so SensorProperty's subscriber count goes up by two. m_subscribedSensors
is a QHash with one entry per path though. The first unsubscribeSensors() call
takes that entry and calls sensor->unsubscribe() once; the second call finds
nothing. The count stays at 1 until the client disconnects. The code is the
same on master.
On NVIDIA laptops this keeps nvidia-smi running, which keeps the dGPU out of
D3cold. On my machine that is about 7 W extra on battery. Related: bug 497024.
Tracking the number of subscriptions per path in Client and only calling
sensor->unsubscribe() when it reaches zero fixes it for me.
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