https://bugs.kde.org/show_bug.cgi?id=460621
Bug ID: 460621
Summary: kcalc: high energy use due to
KCalculator::resizeEvent() storm
Classification: Applications
Product: kcalc
Version: 22.08.2
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: ete...@alum.rit.edu
Reporter: janne-...@jannau.net
Target Milestone: ---
Created attachment 152962
--> https://bugs.kde.org/attachment.cgi?id=152962&action=edit
debug patch removing the resize call in resizeEvent
SUMMARY
Kcalc causes high energy use on Apple Silicon devices (M1 / M2) running Linux
(https://asahilinux.org/). An idle Macbook with kcalc running uses ~9 Watt, the
same system uses 3-4 Watt before starting kcalc and after closing it.
This seems to be caused an endless storm of KCalculator::resizeEvent()s and
resulting redraws. There appears to be a problem with resizing to the minimal
size. This is possibly caused by calling QWidget::resize() from within
KCalculator::resizeEvent(). The Qt documentation warns explicitly about calling
::resize() inside of ::resizeEvent():
https://doc.qt.io/qt-5/qwidget.html#size-prop . I'm not sure if this is the
endless recursion warned about in the documentation. If so the event handling
prevents unlimited memory use one would expect from an endless recursion.
Commenting "KCalculator::resize(minSize);" in KCalculator::resizeEvent()
prevents issue but results in window 1 pixel narrower than the minimal size.
STEPS TO REPRODUCE
1. start kcalc
OBSERVED RESULT
kcalc uses between 65% (kcalc window is on-screen) and 80% (kcalc window is
behind) of a single CPU core
EXPECTED RESULT
kcalc uses almost no CPU when idle
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: AsahiLinux (Qt/KDE packages are identical to ArchLinux ARM)
(available in About System)
KDE Plasma Version: 5.25.5, 5.26.0
KDE Frameworks Version: 5.98.0, 5.99.0
Qt Version: 5.15.6
ADDITIONAL INFORMATION
System is running Plasma (X11) with modeset driver, simpledrm and llvmpipe
Running kcalc with the attached kcalc_resize_debug.diff results in following
output:
| resizeEvent: actual: 490x396 min: 490x396 old: 4294967295x4294967295
| resizeEvent: actual: 489x396 min: 490x396 old: 490x396
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