Bug 506736

Summary: task switcher with "Show selected window" freezes desktop for 1-2 sec when starting and stopping
Product: [Plasma] kwin Reporter: andy <andy>
Component: effects-tabboxAssignee: KWin default assignee <kwin-bugs-null>
Status: RESOLVED WORKSFORME    
Severity: normal CC: kdedev
Priority: NOR    
Version First Reported In: 6.3.5   
Target Milestone: ---   
Platform: Arch Linux   
OS: Linux   
Latest Commit: Version Fixed In:
Sentry Crash Report:

Description andy 2025-07-07 20:40:53 UTC 
SUMMARY
With task switcher "Show selected window" enabled, when pressing Alt+Tab the whole desktop freezes for 1-2 seconds, then while still holding Alt, pressing Tab or Shift-tab works as expected, finally releasing Alt to pick the window freezes the desktop again for another 1-2 seconds. By freezing the desktop I mean, screen does not refresh, moving the mouse the cursor is still.

STEPS TO REPRODUCE
1. In Task Switcher settings, just enable "Show selected window". The type of visualization (e.g. Compact) is unchecked.
2. Hold Alt and press Tab
3. Keep holding Alt and press Tab a few more times
4. Release Alt

OBSERVED RESULT
- Screen is frozen 1-2 seconds on first Alt+Tab press. Mouse doesn't move, screen doesn't update.
- Then we see each window as expected continuing to cycle with more Tab presses. No lag here.
- When Alt is finally released, the screen is frozen again for 1-2 seconds before switching to that window.

EXPECTED RESULT
- The desktop should not freeze when pressing Alt+Tab or releasing it

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: arch linux 6.15.2-arch1-1
KDE Plasma Version: 6.3.5
KDE Frameworks Version: 6.15.0
Qt Version: 6.9.1

ADDITIONAL INFORMATION
- Wayland session
- RTX 5070 Ti graphics card, nvidia-open drivers
- single 4k monitor with 120Hz refresh rate

This sounds similar but not quite https://bugs.kde.org/show_bug.cgi?id=393139

Trying without "Show selected window" checked, all the Compact, Cover Switch, ... types seem to work fine without any lag.
Comment 1 TraceyC 2025-07-11 20:00:53 UTC 
I'm not able to reproduce this with Plasma 6.4.2 and git-master.

Can you please re-test when your system updates to 6.4.2 or later? If you can still reproduce it, please change this back to REPORTED. Thanks!
Comment 2 Bug Janitor Service 2025-07-26 03:46:35 UTC 
🐛🧹 ⚠️ This bug has been in NEEDSINFO status with no change for at least 15 days. Please provide the requested information, then set the bug status to REPORTED. If there is no change for at least 30 days, it will be automatically closed as RESOLVED WORKSFORME.

For more information about our bug triaging procedures, please read https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging.

Thank you for helping us make KDE software even better for everyone!
Comment 3 Bug Janitor Service 2025-08-10 03:46:25 UTC 
🐛🧹 This bug has been in NEEDSINFO status with no change for at least 30 days. Closing as RESOLVED WORKSFORME.