Bug 344175

Summary:	While switched from an X KDE session to an alternate virtual terminal, kwin uses 100% CPU, usually.
Product:	[Plasma] kwin	Reporter:	James <james>
Component:	general	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED DUPLICATE
Severity:	normal
Priority:	NOR
Version First Reported In:	unspecified
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description James 2015-02-14 20:10:52 UTC

Arch Linux
kdebase-workspace 4.11.16-1

$ kwin -v
QDBusConnection: session D-Bus connection created before QCoreApplication. Application may misbehave.
Qt: 4.8.6
KDE Development Platform: 4.14.5
KWin: 4.11.16

AMD Phenom 8400 Triple-Core Processor
AMD/ATI Redwood PRO Radeon HD 5570
running two displays

When and while switched to another Virtual Terminal - where in Arch Linux, Xorg runs in the same VT where it is started - and whether logged into the VT or not, kwin will often, but not always, use 100% CPU on one core.  Switching back to X KDE seems to always return CPU usage to normal.

Reproducible: Sometimes

Steps to Reproduce:
1.Ctrl-Alt-F2
2.
3.

Actual Results:  
kwin uses 100% CPU on one core.

Expected Results:  
kwin CPU usage decreases.

Comment 1 Thomas Lübking 2015-02-14 20:32:38 UTC

please attach the output of
qdbus org.kde.KWin /KWin supportInformation

This is (likely) due to vertical sync, the driver will perform a busy wait for a retrace that does never occur.
As workaround, suspend compositing before switching VT.

Pre-emptive duping.

*** This bug has been marked as a duplicate of bug 330954 ***

Comment 2 James 2015-02-15 04:25:01 UTC

I am posting to Bug 330954.