Bug 1223317 - Qt applications may suffer from heavy UI stalls
Summary: Qt applications may suffer from heavy UI stalls
Status: NEW
Alias: None
Product: openSUSE Distribution
Classification: openSUSE
Component: KDE Workspace (Plasma) (show other bugs)
Version: Leap 15.5
Hardware: All openSUSE Leap 15.5
: P5 - None : Normal (vote)
Target Milestone: Leap 15.5
Assignee: E-Mail List
QA Contact: E-mail List
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Reported: 2024-04-23 16:22 UTC by Tom Mbrt
Modified: 2024-04-28 08:38 UTC (History)
0 users

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Description Tom Mbrt 2024-04-23 16:22:44 UTC 
My first bug report here, pls. be kind.

Facts:

* https://bugreports.qt.io/browse/QTBUG-109511
* openSUSE Leap 15.5 is currently shipping Qt 6.4.2


Observed Effects:

Qt 6.4.0 has introduced a new "feature", which offloads some parts of rendering activity (blending, RGB conversions, etc.) to the global instance of the QThreadPool. This global instance is public and docs advise applications to use this pool.

Any application which uses this pool for offloading several potentially long running tasks, will experience heavy stalls in drawing their UI. Because the UI thread is offloading simple drawing activities into that always crowded pool, and therefore continuously being put asleep by the OS.

Solution:

There are two:

1. Either update openSUSE Leap 15.5 to ship Qt 6.4.3, or
2. create a patch which removes offloading to the QThreadPool in various place listed e.g. here: https://codereview.qt-project.org/c/qt/qtbase/+/462755