[Bug 104343] New: ZaphodHeads + TearFree cause what looks like severe double buffering synchronization problems

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=104343

            Bug ID: 104343
           Summary: ZaphodHeads + TearFree cause what looks like severe
                    double buffering synchronization problems
           Product: xorg
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/intel
          Assignee: chris at chris-wilson.co.uk
          Reporter: werner at almesberger.net
        QA Contact: intel-gfx-bugs at lists.freedesktop.org

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).

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