Re: [Powertop] USB devices get wrong power use values

On (09/22/13 16:54), Marc MERLIN wrote:
> So, I asked on the linux-usb list, and one thing I quickly found out is that the
> Watt value given by powertop 2.4 is way off for USB devices:
> 
> Alan Stern wrote the following:
> 
> Do you have a bug on powertop 2.4 mis-calculating USB power use, both when 
> power is plugged in and when it's not?

powertop uses

	/sys/bus/usb/devices/%s/power/active_duration
and
	/sys/bus/usb/devices/%s/power/connected_duration

	-ss

> Thanks,
> Marc
> 
> On Sun, Sep 22, 2013 at 12:38:56PM -0400, Alan Stern wrote:
> > > > gandalfthegreat:/sys/bus/usb/devices/3-1.6/power# grep . *
> > > > active_duration:61227648
> > > > async:enabled
> > > > autosuspend:2
> > > > autosuspend_delay_ms:2000
> > > > connected_duration:66830880
> > > > control:auto
> > > > level:auto
> > > > persist:1
> > > > runtime_active_kids:0
> > > > runtime_active_time:18870052
> > > > runtime_enabled:enabled
> > > > runtime_status:active
> > > > runtime_suspended_time:5324088
> > > > runtime_usage:0
> > >
> > > This all looks correct.
> >
> > Since then, I've confirmed that I don't have the problem some time after
> > reboot. It may be that the device doesn't seem to sleep well after I've used
> > it once.
> >
> > What's interesting, is that I see this when power is plugged in:
> >
> > Power est.  Events/s    Category       Description
> >   8.18 W    100.0%      Device         USB device: Yubico Yubikey II (Yubico)
> >   8.13 W    100.0%      Device         USB device: Integrated Camera (Chicony Electronics Co., Ltd.)
> >
> > Once I go to batteries, I see this:
> > Summary: 760.1 wakeups/second,  718.9 GPU ops/seconds, 0.0 VFS ops/sec and 6.9% CPU use
> >
> > Power est.              Usage       Events/s    Category       Description
> >   8.32 W    100.0%                      Device         USB device: Yubico Yubikey II (Yubico)
> >   2.52 W     73.3%                      Device         Display backlight
> >
> > Somehow I know that my Yubikey isn't using 8W, so powertop numbers need to
> > be taken with a grain of salt.
> 
> I don't know where powertop gets its numbers from.  Perhaps it uses the
> value reported by the device (bMaxPower).  That value is only a
> maximum; it doesn't change to reflect the actual usage.
> 
> -- 
> "A mouse is a device used to point at the xterm you want to type in" - A.S.R.
> Microsoft is to operating systems ....
>                                       .... what McDonalds is to gourmet cooking
> Home page: http://marc.merlins.org/
>