D19867: [X11] Force glXSwapBuffers to block with NVIDIA driver

ekurzinger added a comment.


  Alright, I think I see what the issue is. For context, on PRIME systems, since there isn't actually a display connected to the NVIDIA GPU, we rely on xf86-video-modeset, which drives the Intel GPU, to call to our driver after each vblank. However, it will actually only do so if there has been damage to the screen. So what I think we have here is QtQuick's thread waiting on this vblank signal before swapping buffers (since we set MaxFramesAllowed to 1), and KWin's main compositing thread waiting on the QtQuick thread. Since KWin isn't rendering to the screen while it waits, no damage occurs and hence this vblank signal is never sent. I think some timeout is what eventually gets things going again (after about 30 seconds). Does that make sense?
  
  So to fix this, I'm wondering if there would be some way to get KWin to do a compositing cycle before it waits on the QtQuick thread?

REPOSITORY
  R108 KWin

REVISION DETAIL
  https://phabricator.kde.org/D19867

To: ekurzinger, #kwin, zzag, davidedmundson
Cc: graesslin, eszlari, davidedmundson, zzag, kwin, jraleigh, GB_2, mkulinski, ragreen, jackyalcine, Pitel, iodelay, bwowk, ZrenBot, ngraham, alexeymin, lesliezhai, ali-mohamed, hardening, jensreuterberg, abetts, sebas, apol, mart