power-usage-report: Find power drain causes

Part of our efforts to reduce power consumption in Ubuntu is to provide an easy tool to hunt down which programs and devices are to blame for inordinate power consumption. powertop’s interactive mode is pretty good for this if you are sitting in a train and want to tweak some knobs to max out battery life, but we need something more reproducible and noninteractive for developers who want to file proper bug reports.

So I wrote a little script power-usage-report which calls fatrace for measuring file access activity from programs, and powertop-1.13 to measure process and device wakeups, clean up and sort their ouput, and generate a report which is appropriate to attach to bug reports, send around, put into Jenkins for measuring daily progress, etc. It is now part of fatrace version 0.4, so today’s Precise upgrades will have it.

The output has several sections for disk access (which prevent the disk from spinning down), wakeups (causing CPU power usage), and device activity. Disk/wakeups are sorted in descending order by process:

$ sudo power-usage-report
Measurement will begin in 5 seconds. Please make sure that the
computer is idle, i. e. do not press keys, start or operate programs, and that
programs are not busy with active tasks other than the one you want to examine.
Starting measurement for 60 seconds...
Measurement complete. Generating report...
======= unity-panel-ser: 5 file access events ======
/usr/share/zoneinfo/UTC: 1 reads
/etc/timezone:
/usr/share/zoneinfo/posix/Europe/Berlin: 1 reads
/etc/localtime: 3 reads

======= gnome-settings-: 1 file access events ======
/etc/fstab: 1 reads

======= telepathy-gabbl: 1 file access events ======
/home/martin/.cache/wocky/caps/caps-cache.db: 1 reads

====== Wakeups ======
  30,9% ( 52,0)   compiz
  16,3% ( 27,4)   [iwlwifi] <interrupt>
  12,5% ( 21,0)   [i915] <interrupt>
   3,7% (  6,3)   [ahci] <interrupt>
   2,3% (  3,9)   swapper/3
   1,2% (  2,0)   gvfs-afc-volume
[...]

====== Devices ======
An audio device is active 100,0% of the time:
hwC0D0 Conexant CX20585 

Recent USB suspend statistics
Active  Device name
100,0%  USB device 1-1.5.4.4 : USB Mouse (A4Tech)
100,0%  /sys/bus/usb/devices/1-1.5.4.2
100,0%  USB device 1-1.5.4 : Kinesis Keyboard Hub (PI Engineering)
  0,0%  USB device 1-1.5.2 : USB2.0 Hub Controller (NEC Corporation)

[...]

You can redirect output to a file, of course. The top header (“Starting measurement..” etc.) will go to stderr and thus not be part of the redirected output.

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