[modeset] Screen tearing when using multiple monitors

[Matt Austin]

I have the WD19TB Thunderbolt dock connected to a Dell Latitude 7480 laptop with two external displays. The laptop itself is closed (internal display is not used).

In a gnome xorg session, there is severe tearing on parts of the screen when dragging windows or scrolling content.

Under a wayland session there is no screen tearing, but I have keyboard key repetition problems which make this mostly unusable day-to-day (https://bugs.launchpad.net/ubuntu/+source/mutter/+bug/1849405).

I can supply short phone videos of tearing occurring on the screens if required.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: mutter 3.28.4-0ubuntu18.04.2
ProcVersionSignature: Ubuntu 5.0.0-36.39~18.04.1-generic 5.0.21
Uname: Linux 5.0.0-36-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.9
Architecture: amd64
CurrentDesktop: GNOME
Date: Tue Nov 19 14:02:09 2019
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_AU.UTF-8
 SHELL=/bin/bash
SourcePackage: mutter
UpgradeStatus: No upgrade log present (probably fresh install)

[Sebastien Bacher (seb128)]

Thank you for your bug report. What video card/driver do you use? Do you use some scaling/what values?

[Sebastien Bacher (seb128)]

Could you also add your 'journalctl -b 0' log from a session having the issue?

[Matt Austin (mattaustin)]

  *-display
       description: VGA compatible controller
       product: HD Graphics 620
       vendor: Intel Corporation
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 02
       width: 64 bits
       clock: 33MHz
       capabilities: pciexpress msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:140 memory:eb000000-ebffffff memory:a0000000-afffffff ioport:f000(size=64) memory:c0000-dffff

The two monitors are 2560x1440, with no scaling. But I do use a 1.25 font scaling factor in gnome-tweaks.

I am using the ubuntu-x-swat ppa, which was an attempt to resolve some previous graphics issues, but I can try removing this again if you'd like me to test?

libdrm-amdgpu1: ubuntu-x-swat/updates/ubuntu
libdrm-common: ubuntu-x-swat/updates/ubuntu
libdrm-dev: ubuntu-x-swat/updates/ubuntu
libdrm-intel1: ubuntu-x-swat/updates/ubuntu
libdrm-nouveau2: ubuntu-x-swat/updates/ubuntu
libdrm-radeon1: ubuntu-x-swat/updates/ubuntu
libdrm2: ubuntu-x-swat/updates/ubuntu
libegl-mesa0: ubuntu-x-swat/updates/ubuntu
libegl1-mesa: ubuntu-x-swat/updates/ubuntu
libgbm1: ubuntu-x-swat/updates/ubuntu
libgl1-mesa-dev: ubuntu-x-swat/updates/ubuntu
libgl1-mesa-dri: ubuntu-x-swat/updates/ubuntu
libgl1-mesa-glx: ubuntu-x-swat/updates/ubuntu
libglapi-mesa: ubuntu-x-swat/updates/ubuntu
libglx-mesa0: ubuntu-x-swat/updates/ubuntu
libllvm9: ubuntu-x-swat/updates/ubuntu
libxatracker2: ubuntu-x-swat/updates/ubuntu
mesa-common-dev: ubuntu-x-swat/updates/ubuntu
mesa-va-drivers: ubuntu-x-swat/updates/ubuntu
mesa-vdpau-drivers: ubuntu-x-swat/updates/ubuntu

[Daniel van Vugt (vanvugt)]

Note that tearing on all-but-one monitor in Xorg sessions is expected. It's an unfortunate feature of Xorg with DRI2. If you can convince the system to use DRI3 and TearFree then that avoids it. But that feature also doesn't exist for all graphics drivers.

Please run:

  lspci -k > lspcik.txt

and attach 'lspcik.txt' as well as your $HOME/.local/share/xorg/Xorg.0.log

[Daniel van Vugt (vanvugt)]

Triaged. This tearing with multiple monitors is a known consequence of the Xorg modesetting driver.

The upstream bug is https://gitlab.freedesktop.org/xorg/xserver/issues/244 (shared with bug 1846398, which needs a similar fix).

[Juan Pedraza (juan-pedraza)]

 I am using the free drivers for my Nvidia card, since the private
  drivers gave more trouble than ever. I reported it too and the
  suggestion they gave me was to remove them and use the free drivers,
  but I have a serious problem with screen tearing, and I can't find a
  solution anywhere about it.

I have Nvidia card and Integrated video Intel, Use Ubuntu 20.04 with a clean installing

[Daniel van Vugt (vanvugt)]

New fix proposed upstream:
https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1006