The quick.controls2/delegates_scrollbar and quick.controls2/delegates_textarea QMLBench benchmarks shows that performance has regressed on the 17th of June. 

https://testresults.qt.io/grafana/d/5ei7yHViz/qmlbench-daily-results?orgId=1&from=2024-08-31T22:00:00.000Z&to=2025-09-29T22:00:00.000Z&timezone=browser&var-suite=$__all&var-benchmark=multiview.qml&var-benchmark=modelaccess_size.qml&var-benchmark=modelaccess_rect.qml&var-benchmark=modelaccess_point.qml&var-benchmark=modelaccess_datetime.qml&var-benchmark=modelaccess_color.qml&var-benchmark=delegates_tumbler.qml&var-benchmark=delegates_textfield.qml&var-benchmark=delegates_textarea.qml&var-benchmark=delegates_switch.qml&var-benchmark=delegates_spinbox.qml&var-benchmark=delegates_slider.qml&var-benchmark=delegates_scrollview.qml&var-benchmark=delegates_scrollbar.qml&var-benchmark=delegates_rowlayout.qml&var-benchmark=delegates_qobject.qml&var-benchmark=delegates_menuitem.qml&var-benchmark=delegates_menu_custom.qml&var-benchmark=delegates_itemdelegate.qml&var-benchmark=delegates_item_childrenRect.qml&var-benchmark=date_getYear.qml&var-branch=dev&var-branch=6.9&var-hardwareId=Ubuntu_22.04_Foucault_x64&var-CoV=hide&var-graphicsApi=opengl&viewPanel=panel-20-clone-13 

Bisecting indicates that this was caused by https://codereview.qt-project.org/c/qt/qtdeclarative/+/644037. Reverting the change brings back all the lost performance.  

delegates_scrollbar and delegates_textarea were tested manually and confirmed to be affected by this patch. Other benchmarks on the dashboard linked below are also likely to be affected by it.

https://testresults.qt.io/grafana/d/5ei7yHViz/qmlbench-daily-results?orgId=1&from=2024-08-31T22:00:00.000Z&to=2025-08-31T22:00:00.000Z&timezone=browser&var-suite=$__all&var-benchmark=multiview.qml&var-benchmark=modelaccess_size.qml&var-benchmark=modelaccess_rect.qml&var-benchmark=modelaccess_point.qml&var-benchmark=modelaccess_datetime.qml&var-benchmark=modelaccess_color.qml&var-benchmark=delegates_tumbler.qml&var-benchmark=delegates_textfield.qml&var-benchmark=delegates_textarea.qml&var-benchmark=delegates_switch.qml&var-benchmark=delegates_spinbox.qml&var-benchmark=delegates_slider.qml&var-benchmark=delegates_scrollview.qml&var-benchmark=delegates_scrollbar.qml&var-benchmark=delegates_rowlayout.qml&var-benchmark=delegates_qobject.qml&var-benchmark=delegates_menuitem.qml&var-benchmark=delegates_menu_custom.qml&var-benchmark=delegates_itemdelegate.qml&var-benchmark=delegates_item_childrenRect.qml&var-benchmark=date_getYear.qml&var-branch=dev&var-branch=6.9&var-hardwareId=Ubuntu_22.04_Foucault_x64&var-CoV=hide&var-graphicsApi=opengl