[Interest] QtQuick/QML performance issue

[VStevenP]

I'm trying to understand a curious performance problem I observe in my QtQuick apps.

First off, here's something good:  If I have a simple app that contains one Knob widget, editing that knob causes 'top' to show a CPU% of ~7% (typical) and ~15% (max).  When the app is idle, top reports CPU% of 0.  This is all good.

However, if I add 20 different widgets to the app, then do the same edit test on that single Knob, 'top' shows a CPU range that is now in the ~30-40% range and ~45% (max).    When the app is idle, top again reports CPU% of 0.

Why does the single edited Knob appear to use so much more processing power when there are a number of other idle widgets in the QtQuick app?

I am observing this on a BeagleBoard-xM, which is a supported platform for Boot to Qt.  I have cross-built Qt 5.2 for ARM with configure -release.  The BeagleBoard-xM is running at top speed on the GPU and CPU (400/1000).  DVFS features are not engaged.

I really needs to find out if I can make a Qt Quick app which runs on the BB-xM that can have a couple dozen widgets and when I use one of them, it will not use so much of the CPU.


Does anybody have any ideas how to avoid this problem?

- VStevenP