https://bugs.kde.org/show_bug.cgi?id=409097
Bug ID: 409097
Summary: kscreenlocker_greet using 100% cpu when in another
user's session
Product: kscreenlocker
Version: unspecified
Platform: Debian testing
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: greeter
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
SUMMARY
kscreenlocker_greet process consumes 100% CPU if it starts up when that user
isn't the active user, i.e. that user is not currently using the display. Note
that that although this looks similar to bug #347772, it isn't the same bug.
STEPS TO REPRODUCE
1. Have 2 users logged into X
2. In user1's session:
sleep 5 ; kscreenlocker_greet
3. Immediately switch to user2 with e.g. <ctrl><alt><f8>
OBSERVED RESULT
After 5 seconds, user1's kscreenlocker_greet process starts and immediately
consumes 100% CPU. 100% CPU is also used if that user's kscreenlocker_greet
process is started automatically by plasma when the idle period expires,
provided that I've already switched to another user. This is 100% reproducible
for me. If I lock screen manually or run e.g. kscreenlocker_greet --graceTime
5000 then everything is fine.
Although I'm running debian testing (libkscreenlocker5 5.14.5-1), I've also
tried downloading the latest source of kscreenlocker/greeter from git.
Adding ProfilerStart()/ProfilerStop() from Google's perf tools around
app.exec() in main.cpp of greeter hasn't been very useful as it appears that
CPU is being used somewhere in QSGBatchRenderer::Renderer::renderMergedBatch()
which seems to be calling _nv023glcore() (somewhere in Nvidia's driver
presumably).
I'm assuming the problem is that something is trying to access the display, but
can't, because it's being used by another user. However, as this could be quite
common in a multi-user setup, perhaps there's something different about the way
kscreenlocker_greet does it?
EXPECTED RESULT
kscreenlocker_greet should use <1% CPU.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Debian testing
KDE Plasma Version: 5.14.5
KDE Frameworks Version: 5.54.0
Qt Version: 5.11.3
Nvidia drivers: 418.74
ADDITIONAL INFORMATION
kcachegrind output:
http://www.mettalogic.co.uk/tim/tmp/screenlock_cachegrind.png
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