Mouse slow in Xorg fractional scaling

[Sevi]

I have a Dell XPS 17 with a 3,840 x 2,400 screen and an external monitor with 3840 x 1600 resolution. When I use only one of them it works totally fine. I use the external monitor without scaling and my notebook display with fractional scaling of 150%. But when i want to use both at the same time, my mouse starts to be slow. So in this scenario i have the external monitor at 100% and the notebook screen at 150%. Everything works fine expect the mouse which is slow,on both screens. What I found is, when i set both my screens to 200% while fractional scaling is enabled. The issue is gone. Same with 100%. But as soon as I start using fractions, the mouse is slow again. I don't believe it is an power issue because my hardware is mostly in idle. Also, i tried different mouses over Bluetooth and USB but no change.

I am currently using 20.10 but had the same issue with 20.04. But when i use Wayland, the problem is gone.

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: xorg 1:7.7+19ubuntu15
ProcVersionSignature: Ubuntu 5.8.0-26.27-generic 5.8.14
Uname: Linux 5.8.0-26-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
.proc.driver.nvidia.capabilities.gpu0: Error: [Errno 21] Is a directory: '/proc/driver/nvidia/capabilities/gpu0'
.proc.driver.nvidia.capabilities.mig: Error: [Errno 21] Is a directory: '/proc/driver/nvidia/capabilities/mig'
.proc.driver.nvidia.gpus.0000.01.00.0: Error: [Errno 21] Is a directory: '/proc/driver/nvidia/gpus/0000:01:00.0'
.proc.driver.nvidia.registry: Binary: ""
.proc.driver.nvidia.suspend: suspend hibernate resume
.proc.driver.nvidia.suspend_depth: default modeset uvm
.proc.driver.nvidia.version:
 NVRM version: NVIDIA UNIX x86_64 Kernel Module 450.80.02 Wed Sep 23 01:13:39 UTC 2020
 GCC version: gcc version 10.2.0 (Ubuntu 10.2.0-13ubuntu1)
ApportVersion: 2.20.11-0ubuntu50
Architecture: amd64
BootLog: Error: [Errno 13] Permission denied: '/var/log/boot.log'
CasperMD5CheckResult: skip
CompositorRunning: None
CurrentDesktop: ubuntu:GNOME
Date: Sun Nov 1 14:01:59 2020
DistUpgraded: 2020-10-30 12:11:16,382 ERROR got error from PostInstallScript ./xorg_fix_proprietary.py (g-exec-error-quark: Failed to execute child process “./xorg_fix_proprietary.py” (No such file or directory) (8))
DistroCodename: groovy
DistroVariant: ubuntu
DkmsStatus:
 evdi, 1.7.0, 5.8.0-26-generic, x86_64: installed
 nvidia, 450.80.02, 5.8.0-26-generic, x86_64: installed
 soundwire, 1.2.2: added
DpkgLog:

ExtraDebuggingInterest: Yes
GraphicsCard:
 Intel Corporation UHD Graphics [8086:9bc4] (rev 05) (prog-if 00 [VGA controller])
   Subsystem: Dell UHD Graphics [1028:098f]
 NVIDIA Corporation TU106M [GeForce RTX 2060 Max-Q] [10de:1f12] (rev a1) (prog-if 00 [VGA controller])
   Subsystem: Dell TU106M [GeForce RTX 2060 Max-Q] [1028:098f]
InstallationDate: Installed on 2020-09-19 (42 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
MachineType: Dell Inc. XPS 17 9700
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.8.0-26-generic root=UUID=6d098ea0-9d87-46ec-beb0-cc19a3b20841 ro quiet splash resume=UUID=723b6007-ad35-4e89-be9e-341d54fe18f8 nouveau.modset=0
SourcePackage: xorg
Symptom: display
UpgradeStatus: Upgraded to groovy on 2020-10-30 (2 days ago)
dmi.bios.date: 08/18/2020
dmi.bios.release: 1.3
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 1.3.2
dmi.board.name: 0P1CHN
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 10
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvr1.3.2:bd08/18/2020:br1.3:svnDellInc.:pnXPS179700:pvr:rvnDellInc.:rn0P1CHN:rvrA00:cvnDellInc.:ct10:cvr:
dmi.product.family: XPS
dmi.product.name: XPS 17 9700
dmi.product.sku: 098F
dmi.sys.vendor: Dell Inc.
version.compiz: compiz N/A
version.libdrm2: libdrm2 2.4.102-1ubuntu1
version.libgl1-mesa-dri: libgl1-mesa-dri 20.2.1-1
version.libgl1-mesa-glx: libgl1-mesa-glx N/A
version.nvidia-graphics-drivers: nvidia-graphics-drivers-* N/A
version.xserver-xorg-core: xserver-xorg-core 2:1.20.9-2ubuntu1
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:19.1.0-1ubuntu1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20200714-1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.16-1

[Sevi (sevimuelli)]

I forgot to say that this problem is only with the external mouse. With the touch pad, i have no issue.

I have an RTX 2060 Max-q in my notebook with Nvidia driver installed but it is deactivated as on demand. But even if I enable this card, it has no effect.

I believe that because of the fractional scaling, the reading of the input device gets somehow mixed up.

[Daniel van Vugt (vanvugt)]

This bug is somewhat expected because fractional scaling works by rendering the desktop at a higher resolution than your screen. So it will take more mouse movement for the pointer to cross the screen.

Integer scaling doesn't work that way so the mouse should move at "normal" speed there.

[Dimitrij Mijoski (dimztimz)]

I too can confirm this. I have much simpler configuration, a single 17-inch laptop with full HD resolution. OS version is Ubuntu 20.04.

Under X11, if I select any fractional scaling above 100%, the mouse cursor moves slower via the touchpad. Under Wayland there are no problems on any scaling.

[Emmett Keyser (ekeyser)]

Daniel, no, fractional scaling does not render the desktop at a higher resolution than your screen. Unless you are talking about xorg "Screen"s. Fractional scaling renders in a _lower_ resolution. And a bug is never expected - hence why it's called a bug. I don't even know why you would categorize it as expected. Saying something about resolution doesn't clear up why mouse tracking all of a sudden incorporates latency.

I'm not even sure many people like fractional scaling. If one could simply choose different integer scaling for different monitors that would solve 90% of people's problems.

[Daniel van Vugt (vanvugt)]

> fractional scaling does not render the desktop at a higher resolution than your screen

Xorg fractional scaling DOES render the desktop internally at higher resolution than the monitor, and then downscales it to the physical monitor. That's how you get a "fraction". For example:

  Monitor = 3840x2160
  Scale = 150%
  Render resolution = 5120x2880
  Transform matrix scale factor = 1.333
  Final visible resolution = 5120x2800 / 1.333 = 3840x2160

You can confirm this by looking at the details in 'xrandr --verbose'.

> If one could simply choose different integer scaling for different monitors that would solve 90% of people's problems.

Yes you can already but only in Wayland sessions. Xorg sessions are limited by Xorg itself not treating each monitor as a separate framebuffer.