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Performance issues with Qt 5.9.1 on Windows 7



  • This is probably one of the strangest issue I have come across and also completely stumped trying to debug.
    One of our users running our application on Windows 7 noticed a massive performance issue opening XML files. We have a format of XML and use QXmlStreamReader to open the files. The files can be complicated with several nested tags.
    The same flows used to open faster (1-2 minutes) and currently takes more than 25 minutes to open. I cannot replicate it on Windows 10 and on a Windows 7 VM too. knocked the RAM and CPU down to make sure I can try and narrow the issue but in vain.
    Another strange behaviour is that when the user connects their laptops to the projector then the performance of opening the flow and rendering the file is even slower.

    The application is basically: http://doc.qt.io/qt-5/qtwidgets-graphicsview-diagramscene-example.html
    It has been modified and lots of features added but the files are represented as XML flows.

    Qt version is 5.9.1
    Windows 7
    VS2017

    Any suggestions as to where I can start looking for the culprit code? Or is this a Qt bug. I am suspecting QtWebEngine which we use. Any clues to debug?

    Really appreciate any inputs.



  • I've had a similar problem on Windows 7 laptop, solved by switching the desktop from using Aero to using Windows classic theme.



  • Thanks for that. WOuld have never thought of this. I will report if that helped.



  • @vivian

    I am suspecting QtWebEngine which we use.

    I am intrigued: what is the connection between QWebEngine and XML? (I didn't download the code example, but the text explanation made no mention of "XML".)

    I can understand that QWebEngine's rendering might be affected by desktop theme, as per @hskoglund, but not any connection to QXmlStreamReader.


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