Bug 374740

Summary:	Unplugging controller causes 100% usage of one CPU core
Product:	[Applications] systemsettings	Reporter:	tguen <tguenther.dev>
Component:	kcm_joystick	Assignee:	Unassigned bugs mailing-list <unassigned-bugs>
Status:	RESOLVED FIXED
Severity:	normal	CC:	isma.af, tguenther.dev, xnagytibor
Priority:	NOR
Version:	5.27.3
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:	https://invent.kde.org/plasma/plasma-desktop/-/commit/7fe5642bc3dda5d04e299c2f929c54642964bd22	Version Fixed In:	6
Sentry Crash Report:

Description tguen 2017-01-08 11:08:05 UTC

When in the joystick section of the input settings, unplugging my controller (Sony Dualshock 4) causes 25% CPU usage (quad core CPU -> 100% of one core). Always reproducible.

Comment 1 Christoph Feck 2017-01-10 18:54:08 UTC

Which process?

Comment 2 tguen 2017-01-11 00:04:45 UTC

systemsettings5

It stops using the CPU when I click the 'all settings' button in the top left.

Comment 3 tguen 2021-02-19 08:16:11 UTC

Issue remains in 5.21

Comment 4 Nagy Tibor 2021-10-19 05:48:26 UTC

I can also reproduce this with 5.23. I may be entirely wrong but this is what I see happening:

1. You pull out the joystick cable.
2. Joystick's device file gets nuked.
3. This select call [1] starts always returning immediately without timeouts. No errors thrown.
4. This read call [2] doesn't read anything anymore. No errors thrown.
5. Event loop goes hyperspeed because of the lack of timeouts.

[1] https://invent.kde.org/plasma/plasma-desktop/-/blob/58f29efd5d2975129c07dcdc4a9eb78669c5eb67/kcms/joystick/joydevice.cpp#L292
[2] https://invent.kde.org/plasma/plasma-desktop/-/blob/58f29efd5d2975129c07dcdc4a9eb78669c5eb67/kcms/joystick/joydevice.cpp#L298

No idea about how to properly fix it though.

Comment 5 Nagy Tibor 2022-03-03 19:23:15 UTC

This bug could be a prime candidate for the KDE Eco project. I don't think these kind of busy loops are environmentally-friendly.

I have no hardware to test it however this bug may also affect the thermals and battery life of Valve's Steam Deck. Their user base is more likely to encounter this bug than the usual desktop KDE users for obvious reasons. And imagine unnecessarily spinning a core 100% on a handheld device where every Wh counts...

Comment 6 tguen 2023-03-21 06:37:28 UTC

Issue remains in 5.27.3

Comment 7 Ismael Asensio 2023-12-01 18:03:54 UTC

Should be fixed with the introduction of the new GameController KCM.
It uses a completely different codepath via SDL2.

Please, feel free to reopen if you still can reproduce it after Plasma 6.