Public bug reported:

Laptop: Lenovo ThinkPad L480
Graphics: Intel UHD Graphics 620 (KBL GT2)
Second monitor: Philips 276E8VJSB/00 4K UHD

There is a big performance degradation in an X11 session + 4K resolution
+ 125% fractional scaling in the second monitor compared to a Wayland
session. The mouse cursor moves very slow, dragging Windows is very
slow, scrolling in Firefox is very laggy, so everything becomes
unusable. The performance degradation applies in both displays even
though fractional scaling is only applied in the second 4K monitor.

Whereas in Wayland, the performance is much better in 4K resolution +
fractional scaling in the second monitor, the mouse cursor and dragging
windows are a lot smoother. I just sometimes notice a slight jump in the
mouse cursor but only in the second monitor, the built-in monitor
behaves normally.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: mutter 3.36.3-0ubuntu0.20.04.1
ProcVersionSignature: Ubuntu 5.4.0-42.46-generic 5.4.44
Uname: Linux 5.4.0-42-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.6
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Fri Aug  7 12:00:26 2020
InstallationDate: Installed on 2020-04-26 (102 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: mutter
UpgradeStatus: No upgrade log present (probably fresh install)

** Affects: mutter (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug focal wayland-session

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https://bugs.launchpad.net/bugs/1890802

Title:
  Big performance degradation in X11 + 4K resolution + fractional
  scaling in second monitor compared to Wayland

Status in mutter package in Ubuntu:
  New

Bug description:
  Laptop: Lenovo ThinkPad L480
  Graphics: Intel UHD Graphics 620 (KBL GT2)
  Second monitor: Philips 276E8VJSB/00 4K UHD

  There is a big performance degradation in an X11 session + 4K
  resolution + 125% fractional scaling in the second monitor compared to
  a Wayland session. The mouse cursor moves very slow, dragging Windows
  is very slow, scrolling in Firefox is very laggy, so everything
  becomes unusable. The performance degradation applies in both displays
  even though fractional scaling is only applied in the second 4K
  monitor.

  Whereas in Wayland, the performance is much better in 4K resolution +
  fractional scaling in the second monitor, the mouse cursor and
  dragging windows are a lot smoother. I just sometimes notice a slight
  jump in the mouse cursor but only in the second monitor, the built-in
  monitor behaves normally.

  ProblemType: Bug
  DistroRelease: Ubuntu 20.04
  Package: mutter 3.36.3-0ubuntu0.20.04.1
  ProcVersionSignature: Ubuntu 5.4.0-42.46-generic 5.4.44
  Uname: Linux 5.4.0-42-generic x86_64
  ApportVersion: 2.20.11-0ubuntu27.6
  Architecture: amd64
  CasperMD5CheckResult: skip
  CurrentDesktop: ubuntu:GNOME
  Date: Fri Aug  7 12:00:26 2020
  InstallationDate: Installed on 2020-04-26 (102 days ago)
  InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=de_DE.UTF-8
   SHELL=/bin/bash
  SourcePackage: mutter
  UpgradeStatus: No upgrade log present (probably fresh install)

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