Arch Linux

chikinn

Member

Registered: 2014-04-09

Posts: 42

[SOLVED] Brightness adjustment is laggy after upgrading to Linux 4.0

Hi all, running on a Vizio CT14-A4 here.

When I press one of the brightness keys (e.g., fn+F4), the system responds correctly, but only after a 1-2 sec delay.  By contrast, writing to the brightness file in

/sys/class/backlight/acpi_video0

still works instantly (no delay).  Note that I have just the one backlight directory (acpi_video0).

Downgrading Linux from 4.0 to 3.19 fixes the problem.  Obviously, though, I'd like to run 4.0 -- any suggestions?

Edit: I should have mentioned, I've tried all of the kernel options listed here.

Last edited by chikinn (2015-12-05 18:52:15)

Tisalgelijk

Member

Registered: 2013-03-08

Posts: 4

Re: [SOLVED] Brightness adjustment is laggy after upgrading to Linux 4.0

Same issue here. Using acpi_listen, I can see that all ACPI events are delayed for a few seconds (and sometimes coming through in bursts). This causes the laggy brightness keys. but also slow detection of AC (un)plugging events.

chikinn

Member

Registered: 2014-04-09

Posts: 42

Re: [SOLVED] Brightness adjustment is laggy after upgrading to Linux 4.0

Today I tried upgrading from 3.19.2 to 4.1.6.  The issue persists so I guess I'm sticking with 3.19.

Would appreciate any nudges in the right direction.  I'm really not sure what to try next here.

Head_on_a_Stick

Member

From: London

Registered: 2014-02-20

Posts: 7,771

Website

Re: [SOLVED] Brightness adjustment is laggy after upgrading to Linux 4.0

The issue persists so I guess I'm sticking with 3.19

It would probably make more sense to switch to the LTS kernel so that you get all the security updates.

---

Are you infected with Wetiko?

chikinn

Member

Registered: 2014-04-09

Posts: 42

Re: [SOLVED] Brightness adjustment is laggy after upgrading to Linux 4.0

That's a great idea, thanks.

Head_on_a_Stick

Member

From: London

Registered: 2014-02-20

Posts: 7,771

Website

Re: [SOLVED] Brightness adjustment is laggy after upgrading to Linux 4.0

Unfortunately, hardware regressions in Linux are not uncommon.

Perhaps a well-formulated bug report would help the kernel team fix this.

https://bugzilla.kernel.org/

---

Are you infected with Wetiko?

frank604

Member

From: BC, Canada

Registered: 2011-04-20

Posts: 1,212

Re: [SOLVED] Brightness adjustment is laggy after upgrading to Linux 4.0

You could do a work around and perhaps map your brightness keys via xbindkeys to xbacklight {-dec|-inc} 5?

chikinn

Member

Registered: 2014-04-09

Posts: 42

Re: [SOLVED] Brightness adjustment is laggy after upgrading to Linux 4.0

You could do a work around and perhaps map your brightness keys via xbindkeys to xbacklight {-dec|-inc} 5?

Yeah, in the end that's more or less what I'm doing.  Only catch is the regular brightness keys are unusable: I can map them to xbacklight, but the delay persists.  What happens is there's still a delay, and then there's the laggy default behavior I mentioned, and THEN the xbacklight call triggers.  So I get two brightness changes, one by default and one from xbacklight.  Both still delayed.

Since I can't get rid of the delay on Fn-F3 and Fn-F4, I instead mapped ALT-MINUS and ALT-PLUS to xbacklight.

The weird thing is I only get a delay on e.g. Fn-F3, no delay with F3 alone.  Other media keys (Fn-F7, etc.) trigger without delays.

I think I was just being stubborn.  Not being able to use the normal brightness keys isn't enough of an inconvenience to justify using an old kernel.  I'll think about submitting that bug report, though.

frank604

Member

From: BC, Canada

Registered: 2011-04-20

Posts: 1,212

Re: [SOLVED] Brightness adjustment is laggy after upgrading to Linux 4.0

Turn off everything that pre-sets your fn keys (DE and acpi kernel commands).  Then you can remap all your fn keys via xbindkeys since it is working as intended on a different keybind without delay.  You should submit a bug report though to help yourself and the rest of the world.

Head_on_a_Stick

Member

From: London

Registered: 2014-02-20

Posts: 7,771

Website

Re: [SOLVED] Brightness adjustment is laggy after upgrading to Linux 4.0

^ A git bisect that pins down the bad commit and a patch to fix it would get the problem fixed much more quickly.

---

Are you infected with Wetiko?

chikinn

Member

Registered: 2014-04-09

Posts: 42

Re: [SOLVED] Brightness adjustment is laggy after upgrading to Linux 4.0

Despite my laziness in not submitting a patch, this appears to be fixed in 4.2!  Marking solved.