[alsa-devel] 100.0% power usage of Device Audio codec (HDA) on wake

[Takashi Iwai]

At Wed, 21 Nov 2012 15:15:09 +0100,
Tomas Pospisek wrote:
> 
> On Tue, 20 Nov 2012 10:01:18 +0100, Takashi Iwai <tiwai at suse.de> wrote:
> > At Tue, 20 Nov 2012 09:56:19 +0100,
> > David Henningsson wrote:
> >> 
> >> On 11/20/2012 09:32 AM, Takashi Iwai wrote:
> >> > At Tue, 20 Nov 2012 09:07:21 +0100,
> >> > David Henningsson wrote:
> >> >>
> >> >> It does put another question - from where does powertop get its
> >> >> values,
> >> >> and do we have to do anything on our side to make sure / aid them
> >> >> being
> >> >> correct?
> >> >
> >> > powertop checks /sys/class/sound/hwC*D*/power_{off|on}_acct files.
> >> > They contain the time (in ms) how long the codec is in the power-save
> >> > mode.
> >> 
> >> Thanks. But I have also recently seen a computer where powertop showed
> a 
> >> Watt number, essentially saying that the codec consumed 1.4 Watts or so
> 
> >> (I don't remember the exact number). Have you seen that too?
> > 
> > When 1.4W is constantly consumed even without PCM, it's a bit too
> > high.  But with PCM playback, about 1W usage can be measured normally,
> > I guess.
> 
> man powertop says:
> 
> --calibrate   runs powertop in calibration mode. When running on battery,
>               powertop can track power consumption as well as system
>               activity. When there are enough measurements,  powertop
>               can  start  to  report  power  estimates.  One can get more
>               accurate estimates by using this option to enable a
>               calibration cycle. This will cycle through various display
>               levesl and USB device activities and workloads.
> 
> So that's what powertop does I think: it estimates.

But 100% things from hwC0D0 has nothing to do with the real power
usage.  It's just the time of HD-audio power-saving mode on and off.


Takashi