https://bugs.kde.org/show_bug.cgi?id=487043
Bug ID: 487043
Summary: Extreme stutters/hangs when using certain desktop
effects when "~/.cache" is on slow storage
Classification: Plasma
Product: kwin
Version: unspecified
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: effects-various
Assignee: kwin-bugs-n...@kde.org
Reporter: alkalinethun...@gmail.com
Target Milestone: ---
Created attachment 169491
--> https://bugs.kde.org/attachment.cgi?id=169491&action=edit
Logs of different Kwin hangs happening from both Kwin's perspective and the
kerne'ls.
SUMMARY
If your "~/.cache" directory is stored on slow storage, such as a spinning disk
or an LVM pool, using QML-based desktop effects like Tiling Editor and Alt+Tab
causes extreme multi-second Kwin hangs.
STEPS TO REPRODUCE
1. Add some kind of slow storage to your system (spinning HDD, LVM pool made of
HDDs, slow network filesystem, etc.)
2. Move "~/.cache" to the slow storage medium and symlink it. Alternatively,
move your entire /home to the slow storage device.
3. Bring up Tiling Editor with Meta+T.
OBSERVED RESULT
Depending on how slow/busy the storage medium is, Kwin will hang for at least 2
seconds, sometimes up to 15 in really bad cases. During this hang, the system
is completely unresponsive - no mouse or keyboard input whatsoeever, and if the
hang is long enough, Kwin will warn in the logs about DRM pageflips taking too
long.
EXPECTED RESULT
The system should stay responsive and Kwin shouldn't hang, even if opening
Tiling Editor takes slightly longer.
SOFTWARE/OS VERSIONS
Linux: 6.8.9-arch1-2 (64-bit)
KDE Plasma Version: 6.0.4
KDE Frameworks Version: 6.2.0
Qt Version: 6.7.0
ADDITIONAL INFORMATION
So far, known-affected effects are:
- Tiling Editor (meta+T)
- Window Overview (meta+W)
- Alt+Tab, when Alt is held down (which brings up the window switcher menu)
It seems to be any effect that uses Qt QML, and other than those three, I
haven't personally tested many.
This is also distro-independent. Other users than myself have reported the
exact same hangs occurring on their system, with the common configuration being
their home directory being stored on slow storage.
I have attached three logs that show the issue happening. One of them is of
what Kwin sees when a hang happens. The two dmesg logs are with extreme verbose
DRM logging enabled, one with two screens plugged in and one with one screen.
These were captured with Xaver Hugil's help, before I suspected it was
disk-related, however maybe there's something useful in there.
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