System Settings Updates/Storage pages lead to high cpu usage even there is no network/io activity

[Vicamo Yang]

In normal case, Arale consumes ~310mA (brightness 1160) when stay in all other system settings pages. But when navigate to either Updates or Storage page, power meter readings raise to 700mA (brightness 1160) immediately and never go down again until screen dim (brightness 60), at which Arale still takes ~600mA while other pages take ~110mA.

STR:
1. disable idle lock at "System Settings" / "Security & Privacy" / "Lock when idle" => Never
2. navigate to "System Settings" / "Updates" and check power meter readings before and after screen dim
3. navigate to "System Settings" / "About this phone" / "Storage" and check power meter readings before and after screen dim

Expect:
Power meter readings go down to 310mA before screen dim and 110mA after.

Actual:
1. Updates page:
power meter readings stay in ~700mA before screen dim and ~600mA after. `top` reveals that system-settings process takes 25% cpu time, unity8 takes ~35%, unity-system-compositor takes 12% constantly.

2. Storage page: power meter readings stay in ~740mA before screen dim and ~620mA after. `top` reveals that system-settings process takes >40% cpu time, unity8 takes 33%, unity-system-compositor takes 12.5% constantly.

$ system-image-cli -i
current build number: 7
device name: arale
channel: ubuntu-touch/rc-proposed/ubuntu
last update: 2015-05-30 00:04:38
version version: 7
version ubuntu: 20150529.1
version device: 20150522-a851049
version custom: 20150529.1

$ apt-cache policy unity8
unity8:
  Installed: 8.02+15.04.20150518.1-0ubuntu2
  Candidate: 8.02+15.04.20150518.1-0ubuntu2
  Version table:
 *** 8.02+15.04.20150518.1-0ubuntu2 0
       1001 http://ppa.launchpad.net/ci-train-ppa-service/stable-phone-overlay/ubuntu/ vivid/main armhf Packages
        100 /var/lib/dpkg/status
     8.02+15.04.20150409.1-0ubuntu1 0
        500 http://ports.ubuntu.com/ubuntu-ports/ vivid/universe armhf Packages

$ apt-cache policy ubuntu-system-settings
ubuntu-system-settings:
  Installed: 0.3+15.04.20150514-0ubuntu1
  Candidate: 0.3+15.04.20150514-0ubuntu1
  Version table:
 *** 0.3+15.04.20150514-0ubuntu1 0
       1001 http://ppa.launchpad.net/ci-train-ppa-service/stable-phone-overlay/ubuntu/ vivid/main armhf Packages
        100 /var/lib/dpkg/status
     0.3+15.04.20150413-0ubuntu1 0
        500 http://ports.ubuntu.com/ubuntu-ports/ vivid/universe armhf Packages

[Vicamo Yang (vicamo)]

Also reproducible on Krillin:

$ system-image-cli -i
current build number: 22
device name: krillin
channel: ubuntu-touch/stable/bq-aquaris.es
alias: ubuntu-touch/ubuntu-rtm/14.09
last update: 2015-06-02 07:17:16
version version: 22
version ubuntu: 20150508
version device: 20150505-db7b5bd
version custom: 20150507-685-29-216

$ apt-cache policy unity8
unity8:
  Installed: 8.02+15.04.20150406~rtm-0ubuntu1
  Candidate: 8.02+15.04.20150406~rtm-0ubuntu1
  Version table:
 *** 8.02+15.04.20150406~rtm-0ubuntu1 0
        500 http://derived.archive.canonical.com/ubuntu-rtm/ 14.09/universe armhf Packages
        100 /var/lib/dpkg/status

$ apt-cache policy ubuntu-system-settings
ubuntu-system-settings:
  Installed: 0.3+15.04.20150430.1~rtm-0ubuntu1
  Candidate: 0.3+15.04.20150430.1~rtm-0ubuntu1
  Version table:
 *** 0.3+15.04.20150430.1~rtm-0ubuntu1 0
        500 http://derived.archive.canonical.com/ubuntu-rtm/ 14.09/universe armhf Packages
        100 /var/lib/dpkg/status

[Vicamo Yang (vicamo)]

netstat, ethstatus and iotop show no network or I/O activity at the two pages.

[Vicamo Yang (vicamo)]

Update summary because one doesn't need a power meter to verify this issue. Just run `top` and you'll find CPU usage rise. I would like to have some profiling on unity/system-settings first, but just have no idea and find no documents to proceed.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Ken VanDine (ken-vandine)]

I can no longer reproduce this issue in the updates panel with ubuntu-system-settings 0.3+15.04.20151201-0ubuntu1, perhaps it was fixed in some recent fixes we've landed in that panel.

I have a branch that fixes the issue in the storage page

[Launchpad Janitor (janitor)]

This bug was fixed in the package ubuntu-system-settings - 0.3+16.04.20151204.1-0ubuntu1

---------------
ubuntu-system-settings (0.3+16.04.20151204.1-0ubuntu1) xenial; urgency=medium

  [ Ken VanDine ]
  * Don't delete previous custom ringtones unless a new custom ringtone
    is selected. Set header titled in the picker. (LP: #1519332)

  [ jonas-drange ]
  * drop /usr/bin/ from USS binary in autopilot tests (LP: #1517488)

 -- Ken VanDine <email address hidden> Fri, 04 Dec 2015 16:18:04 +0000