[Interest] Application at Idle takes 10% of CPU

[Michael Jackson]

I have tracked it down to our use of a QSplitter. If I hide our "left" side then the CPU usage drops to 0~1% while idle. There is a QFrame Derived custom class that is placed into the left side but that custom widget does not do any custom painting that I am aware of. Still digging…

Thanks
Mike Jackson

On Jun 27, 2015, at 10:58 AM, Michael Jackson <imikejackson at gmail.com> wrote:

> Our application seems to take more cpu than I think it should while just sitting "Idle". My machine is a MacBook Pro 2.6GHz Core i7 with 16GB Ram. Running OS X 10.8.5. Using the Activity Monitor our application takes about 10-12% of my CPU time. Using the "Instruments" application to get the heaviest functions I see that QImage::copy is taking up a bunch of time:
> 
> Running Time	Self		Symbol Name
> 2218.0ms   57.2%	2218.0	 	QImage::copy(QRect const&) const
> 2218.0ms   57.2%	0.0	 	 QImage::detach()
> 2218.0ms   57.2%	0.0	 	  QPainter::begin(QPaintDevice*)
> 2218.0ms   57.2%	0.0	 	   QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*)
> 2218.0ms   57.2%	0.0	 	    QWidgetBackingStore::doSync()
> 2218.0ms   57.2%	0.0	 	     QWidgetBackingStore::sync()
> 2218.0ms   57.2%	0.0	 	      QWidgetPrivate::syncBackingStore()
> 2218.0ms   57.2%	0.0	 	       QWidget::event(QEvent*)
> 2218.0ms   57.2%	0.0	 	        QMainWindow::event(QEvent*)
> 2218.0ms   57.2%	0.0	 	         QApplicationPrivate::notify_helper(QObject*, QEvent*)
> 2218.0ms   57.2%	0.0	 	          QApplication::notify(QObject*, QEvent*)
> 2218.0ms   57.2%	0.0	 	           QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*)
> 2218.0ms   57.2%	0.0	 	            QCocoaEventDispatcherPrivate::processPostedEvents()
> 2218.0ms   57.2%	0.0	 	             QCocoaEventDispatcherPrivate::postedEventsSourceCallback(void*)
> 2218.0ms   57.2%	0.0	 	              QCocoaEventDispatcher::processEvents(QFlags<QEventLoop::ProcessEventsFlag>)
> 2218.0ms   57.2%	0.0	 	               QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>)
> 2218.0ms   57.2%	0.0	 	                QCoreApplication::exec()
> 2218.0ms   57.2%	0.0	 	                 main
> 0.0ms    0.0%	0.0	 	                  Main Thread  0x2f66d0
> 
> I figured it was one of our custom paint methods. I went  through our project and systematically commented out all of our custom painting codes and there was no change. We do use a lot of CSS to style our widgets. Would that account for the high CPU usage? This is with Qt 5.4.1 downloaded from Qt.io.
> 
> QTimers maybe? We do some animations using QTimer, though that is supposed to be "on-demand", i.e. it is not a continuous animation.
> 
> I replicated the issue on OS X 10.10 with Qt 5.4.2 on that system. As a sanity check, QtCreator uses 0% while Idle. So I must be something that we are doing wrong in our app. Our application on Windows does not seem to have this issue either.
> 
> Thanks for any help or insights.
> Mike Jackson
> BlueQuartz Software