BQ M10 tablet kworker process constantly at 17% CPU due to auto brightness

[Leopoldo Pena]

In the new BQ M10 tablet I noticed a large battery consumption on idle. between 30-40% battery drain overnight with no activity.

I rebooted the tablet, launched terminal then run # top to check on activity.

the process kworker/0:1 is constantly taking 16.9% CPU.

Not sure if that is expected but it seems rather high to me.

[gonso (ie-ingenieros-edificacion)]

last night, the bq m10 had a battery level of 100% and I put this in airplane mode (no wifi, no GPS, no Bluetooth, never app open), this morning (5 hours later) the battery level was 42%; the device in idle mode has consumed more than 50% of energy

[Leopoldo Pena (leopenausa)]

I can confirm that as well. Battery level dropped 40% overnight for me.

[Pat McGowan (pat-mcgowan)]

Seems there are two issues here.
First the CPU usage by the kernel worker thread, I cannot yet reproduce that. Check out using perf at
http://askubuntu.com/questions/33640/kworker-what-is-it-and-why-is-it-hogging-so-much-cpu

Second the overnight battery drain indicates were are not staying suspended properly which I also see.

I would note that its generally not helpful to turn off the radios, it should not matter to battery life in most cases as they automatically go into low power modes and then off when suspended.

[Leopoldo Pena (leopenausa)]

I tried running a trace to see what is happening:

echo 1 > /proc/sysrq-trigger
then run dmesg

some relevant results linked to kworker (lots of repeated kworker messages)

[ALS/PS] als_get_data 1962 : als_get_data *value =225, *status =2

[power/gpufreq] mt_gpufreq_volt_enable_estate ==0!

[Pat McGowan (pat-mcgowan)]

This is triggered by enabling automatic brightness control

[Leopoldo Pena (leopenausa)]

UPDATE: based on pmcgowan feedback deactivating automatic brightness control fixes this issue, and I can confirm that

[Chunsang Jeong (chunsang)]

From a quick check, it polls pretty often even I'd set the interval bigger. Unfortunately, there's legacy code to use interrupt instead of polling, but it didn't work when enabled it for test. It happens only when the screen is on but needs to be fixed in any way.

[Chunsang Jeong (chunsang)]

MP at https://code.launchpad.net/~chunsang/avila/+git/kernel-3.10/+merge/293057
Checked with the patch that kworker used cpu (1 core) from 1.3% to 1.7% and autobrightness worked same as before.