screen brightness oscillates slowly

[Michael Doube]

I set my backlight on an Intel 965 with xbacklight, for increased battery life and for visual comfort.

]$ xbacklight -set 30

I just noticed an apparent slow oscillation in screen brightness on my laptop (Vaio SZ650), which seems to involve xbacklight (see attached log of changing brightnesses) This oscillation has a period of about 3 minutes (I think), and goes from <10% brightness to the set value (30%).

I'm using Intrepid alpha 4, desktop 64bit

[Michael Doube (michael-doube)]

This is still happening in Intrepid alpha 6 - the following calls to xbacklight were made at intervals of a few seconds, with no manual adjustment of brightness. It then stabilised at 50% brightness. This is on AC, so is there some g-p-m interference going on?

intrepida6@intrepida6-laptop:~$ xbacklight
19.046338
intrepida6@intrepida6-laptop:~$ xbacklight
19.984240
intrepida6@intrepida6-laptop:~$ xbacklight
20.539678
intrepida6@intrepida6-laptop:~$ xbacklight
20.960581
intrepida6@intrepida6-laptop:~$ xbacklight
21.298841
intrepida6@intrepida6-laptop:~$ xbacklight
21.664008
intrepida6@intrepida6-laptop:~$ xbacklight
21.996502

[Hans (hans-eichbaum)]

I found this problem is still being present in the beta of Interpid. I got around it by disabling all backlight control by the gnome-power-management.

[Pedro Villavicencio (pedro)]

Thanks for taking the time to report this bug and helping to make Ubuntu better. Could you please attach the resulting log file of: gnome-power-bugreport.sh &> gpm.log to the report? You might also want to take a look to the Debugging instructions located at https://wiki.ubuntu.com/DebuggingGNOMEPowerManager for submit any other logs related to your problem.Thanks in advance.

[Michael Doube (michael-doube)]

As requested:
]$ gnome-power-bugreport.sh &> gpm.log

[Michael Lustfield (michaellustfield)]

I missed that request. I'm adding mine now and I can reattach a different one when the oscillation is occurring.

Also, I rebuilt my system from a cli install. It seems to be working appropriately, but that's after a single trial.

[Michael Lustfield (michaellustfield)]

I'm no longer experiencing this problem. It's because of one of two reasons.

1. The problem may have been fixed.

2. Since my reinstall, I'm not using an application that was causing a conflict.
 - I'm using gnome-power-manager, nm-applet, and openbox with the xrandr fix.

[Michael Doube (michael-doube)]

I am tempted to agree; when I tried to elicit a backlight oscillation to collect logs, I could not reproduce the behaviour. Perhaps mark this as 'fix released' until we have evidence to the contrary?

[Rory McCann (rorymcc)]

I am still experiencing this problem. I have a sony vaio (I'm not sure which). My backlight Fn keys didn't work however entering

$ xrandr --output LVDS --set BACKLIGHT_CONTROL native

(from bug #176888), allowed me to have control over my backlight. However while on battery, my screen brightness oscillates slowly. While on AC power, I don't experience this problem.

Attached is the output of gnome-power-bugreport.sh > gpm.log

[Michael Lustfield (michaellustfield)]

Did you try this in the current Jaunty release? This issue has been confirmed as resolved in 9.04.

[Rory McCann (rorymcc)]

No I haven't tried it on Jaunty yet. I'm using intrepid at the moment