Bug 513071

Summary:	Regression hardware cursor isn't staying smooth under extreme load
Product:	[Plasma] kwin	Reporter:	Rean <techsav>
Component:	wayland-generic	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	REPORTED ---
Severity:	normal	CC:	nate
Priority:	NOR	Keywords:	efficiency-and-performance, regression
Version First Reported In:	6.4.5
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Rean 2025-12-08 06:32:32 UTC

SUMMARY

Regression hardware cursor isn't staying smooth under extreme load

STEPS TO REPRODUCE
Easiest test compositor-killer

OBSERVED RESULT

Cursor performance degrades  under high usage. 

EXPECTED RESULT

Smooth cursor always

SOFTWARE/OS VERSIONS

Operating System: Arch Linux 
KDE Plasma Version: 6.5.3
KDE Frameworks Version: 6.20.0
Qt Version: 6.10.1

ADDITIONAL INFORMATION

Regression alert The hardware cursor has, at some point during Plasma 6.5.x or maybe with Qt 6.10.x, become sluggish again. It's not as bad as when the hardware cursor wasn't a thing; luckily, it didn't go back to being that bad.

Anyways, I tested a live plasma ISO with an older version of plasma, plasma 6.3.5 using compositor-killer and the mouse movement is buttery smooth with no stutter/sluggish movement whatsoever.

Afterward I tested compositor-killer in the Gnome desktop, and it gives the same result as the old Plasma 6.3.5 test: the cursor is also buttery smooth with no lag whatsoever.

So yep, there's 100% a cursor smoothness regression in the latest Plasma.

Comment 1 Rean 2025-12-08 06:40:38 UTC

Also, the Gnome version I tested is the latest Gnome 49 Wayland session on the same system. I simply installed it and switched using SDDM.

Comment 2 Rean 2025-12-08 07:34:10 UTC

Extra Info

Ever since the hardware cursor and the readability stuff were implemented and triple buffering was added a long time ago, I have been using Plasma for a really long time.

I never ever got cursor lag in Plasma Wayland ever since those merges happened. It's only as of late that I'm getting cursor issues again.

Comment 3 Rean 2025-12-09 16:50:07 UTC

Also, I'm pretty sure this started in Plasma 6.4.5 around the time Qt 6.10 was released. I just didn't report it at the time because I wasn't 100% sure, and I just stuck with it until I realized it also affects all my other computers as well.