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ZaphodHeads + TearFree cause what looks like severe double buffering synchronization problems

Submitted by Werner Almesberger

Assigned to Chris Wilson @ickle

Link to original bug (#104343)

Description

My setup: CPU is i7-7700K using build-in GPU (HD 630), no graphics card, no overclocking or particularly unusual setup.

Displays are three in total: HD (HDMI), 4K (DP), HD (DVI-HDMI). This configuration worked under Ubuntu 17.04 but the middle screen (4K) became unusable after upgrading to 17.10.

The effects look like faulty coordination between drawing and buffer switching. I made a short video:
https://almesberger.net/paste/weird-gfx-raiPhie8.mp4

Note:

  • this happens with and without window manager (fvwm)
  • when trying to play video with mplayer, the screen content barely changed. The video was not shown.
  • SolveSpace (3D CAD) performed almost normally for anything 3D, but menus and other text has issues similar to the ones shown in my video.
  • similar symptoms continued also when I changed the resolution of the 4K display to 1920x1080 in xorg.conf
  • the two HD screens (:0 and :0.2) worked fine all the time

xorg.conf:
https://almesberger.net/paste/xorg-eiTahF5A.conf

Xorg.0.log:
https://almesberger.net/paste/Xorg.0-Jahbie1O.txt

dmesg:
https://almesberger.net/paste/aiPo3ae8.txt

Chris Wilson (ickle) remarked on #intel-gfx that ZaphodHeads and TearFree were an unusual combination and suggested I try to disable TearFree in xorg.conf. After disabling it in all three Device sections, the problem disappeared and all seems fine so far (tried xterm, fvwm, chromium, solvespace, and mplayer).