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  1. Qt
  2. QTBUG-71440

Qt-5.11.1 gui performance regression with MIT-SHM enabled



    • Bug
    • Status: Closed
    • P2: Important
    • Resolution: Done
    • 5.11.1, 5.11.2
    • None
    • None
    • Gentoo Linux x86_64 (amd64)
      Kernel: gentoo-sources-4.14.65
      Graphics: nvidia-driver-387.34
      Xorg: x11-base/xorg-server-1.19.5-r2
    • Linux/X11


      After upgrading from qt-5.9.6 to qt-5.11.1, I've noticed that "kate" application from KDE was starting really slow, with noticeable visual bugs: first it starts in window mode, after a few moments it goes into maximized window mode, but it takes few seconds to actually redraw the window of application.

      I've tried downgrading to qt-5.9.6, and performance issues disappeared. I've also tried resizing window of "konsole" application, result was same: qt-5.9.6 works fine, qt-5.11.1 works very slow and with noticeable visual bugs. KDE applications and libraries remained same version, only qt version changed.

      After that I've tried running kate and konsole in empty openbox session, issues remained with qt-5.11.1.

      After that I've tried qterminal from lxqt (https://github.com/lxqt/qterminal), which is pure qt application, and it had same issues. It uses qtbase, qtdbus and qtx11extras, and it doesn't use qml.

      Also, when using qt-5.11.1, in "top" I see a few "kworker" processes consuming high cpu % when gui of qt application is updated/modified (for example, window is resized). I don't observe such cpu consumption with qt-5.9.6.

      I've bisected qtbase repository from 5.9.6 to 5.11.1 and found first bad commit:

      I've tried using qt-5.11.2, but it didn't fix issue to me.

      Adding following lines to xorg configuration circumvents issue for me:

      Section "Extensions"
          Option "MIT-SHM" "Disable"

      I'm attaching output of xdpyinfo.


        1. build.log
          222 kB
        2. debug-run-5.11.log
          8 kB
        3. Screenshot_20190203_161111.png
          89 kB
        4. vminfo.txt
          1 kB
        5. xdpyinfo.txt
          33 kB
        6. xdpyinfo-ext-all.txt
          60 kB
        7. Xorg.0.log
          30 kB

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              paeglis Gatis Paeglis
              i.dark_templar i.dark_templar
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