bug#71591: 30.0.50; PGTK: Terrible input lag with display scaling

["Jarno Malmari" <jmalmari@ftml.net>]

On Thu, 27 Jun 2024, at 13:56, Po Lu wrote:
> Eli Zaretskii <eliz@gnu.org> writes:
>
>>> From: Jarno Malmari <jmalmari@ftml.net>
>>> Date: Sun, 16 Jun 2024 15:26:13 +0300
>>> 
>>> With a 4k display and 150 % display scaling there is a noticeable input
>>> lag when moving the point around in fullscreen. Very sluggish
>>> feel. Shrinking the window helps.
>>> 
>>> Besides "sluggish feel" I couldn't figure out easily measurable metric
>>> for this. One way is to clock how long it takes to use your keyboard
>>> repeat with `next-line' to reach the end of a couple pages long buffer.
>>> 
>>> This was tested with PGTK build on KDE Plasma 6 running Wayland. X build
>>> running in XWayland does not have this problem even if configured to be
>>> "Scaled by the system" from the system display configuration UI.
>>> 
>>> The scale option that affects this can also be changed with these commands:
>>> 
>>>     kscreen-doctor output.${OUTPUT_NAME}.scale.1.5
>>>     kscreen-doctor output.${OUTPUT_NAME}.scale.1.0
>>> 
>>> Applies also to emacs 29.
>>
>> Po Lu, any suggestions or ideas?
>
> Jarno, does your system use NVIDIA graphics drivers?

No. AMD Rembrandt [Radeon 680M], amdgpu kernel driver.