On 2/10/2012 1:07 AM, Paul Menzel wrote:
> Unfortunately neither `lsof` nor `fuser` returned any process using that
> device.
> 
>         $ sudo lsof /dev/snd/hwC0D0
>         $ sudo fuser -v /dev/snd/hwC0D0

also look for /dev/dsp or similar
> 
>> > or you found a real kernel driver bug ;-)
> Looks like it. I guess I will contact the ALSA list and asking what this
> device is about and if they can fix it.
> 
> Could you answer a last question, please? What is PowerTOP actually
> checking to figure out the usage.


the codec's directory in sysfs (say
/sys/devices/pci0000.00/0000:00:1b.0/sound/card0/hwC0D3) has 2 files,
power_on_acct and power_off_act
these count time that the codec is on or off respectively.
powertop calculates a delta of these two over the measurement interval
(20 seconds), and then since it knows how long it was on and off,
calculates the percentage.
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