Slow response on brightness control - Dell Inspiron 15z, Fedora 29 KDE

asked 2019-01-19 05:05:53 -0500

updated 2019-01-21 11:57:37 -0500

Hi, I recently switched to Fedora 29 KDE, and noticed that the brightness control is very slow. If I try to control the brightness using the Fn keys, it takes about a second to respond, and the CPU usage shoots up to about 75%, which immediately comes back down. I have tried searching around. I found this thread which has no useful responses: https://ask.fedoraproject.org/en/ques...

I also found this thread on AskUbuntu: https://ubuntuforums.org/showthread.p.... I tried what it suggests but it didn't work for me.

I will preemptively add all the information requested on the above thread, in case it's useful. Please let me know if you need some additional diagnostic information from me to figure this out.

$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-4.19.15-300.fc29.x86_64 root=UUID=977b5049-95bd-4043-849d-a2bb9d5ca9e3 ro resume=UUID=1b655533-666d-42dc-9121-e8d0223a3c33 rhgb quiet LANG=en_IN.UTF-8

$ lspci -k | grep -iA2 VGA
00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)
    Subsystem: Dell Device 0590
    Kernel driver in use: i915

$ for interface in /sys/class/backlight/*; do echo -e "\n $interface"; cat $interface/{brightness,max_brightness,actual_brightness}; done

 /sys/class/backlight/intel_backlight
4394
4882
4394

Output of lsmod: https://pastebin.com/cKq5jw76

Output of /var/log/Xorg.0.log: https://pastebin.com/amuBEkGk

Thanks in advance!

EDIT: After further tinkering, I have found that the issue is with Linux interfacing with the keyboard and actually has nothing to with brightness. Even when I removed the shortcut of the F5, F6 keys from the brightness control, even then, pressing the keys causes a spike in CPU usage, when the keys are not even doing anything. On the other hand, changing brightness with the slider or the terminal is instant as it should be. What is also curious is that none of the other Fn keys cause a slowdown. The volume keys, media buttons, touchpad enable/disable button, none of them cause a usage spike. However, the brightness buttons cause a CPU usage spike even when not paired with anything. The model is Dell Inspiron 15z 5523, so if anyone has any solutions for this particular problem, I am all ears!

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