[maemo-users] N900 consumes too much power

From: Eero Tamminen eero.tamminen at nokia.com
Date: Tue Aug 7 12:25:27 EEST 2012

On 08/07/2012 04:20 AM, ext Cedric Cellier wrote:
> Of course offline mode is not normal. I suggested it
> for testing :) So that whatever software is the culprit
> it can no longer drain the battery very fast. If you can't
> stand several days in offline mode and without top reporting
> a process that's heavy on the cpu

It doesn't need to be that heavy.

Even a process that constantly wakes up just at 1s interval,
(which shows only as 0-1% of CPU usage in top) will
reduce device idle use-time from one week[1] to a day.

This is when just CPU is used.  If also network is used,
the wakeups can be much rarer and they still ruin the use-time
even worse.  I'm not completely sure of these numbers, but
if your WLAN accesspoint power management is working, I think
even <5 minute interval wakeups are bad, with phone networks,
the network access intervals need to be much longer for device
to be able to save power.

These kind of wakeup frequencies you don't notice with top, you
need either strace the programs or use e.g. nethogs[3] utility.

Note also that the weaker the network signal strength is,
the more power is required.

[1] A week with a full, *new* battery [2],  no services installed etc.

[2] Battery capacity worsens with time, with use and higher temperatures
     (check the manufacturing date when buying batteries!), see:

[3] http://packages.debian.org/squeeze/nethogs

> then you'll be certain your  hardware is faulty.

	- Eero
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