High CPU usage during music playback

[Michał Sawicz]

When playing music I can see quite high CPU usage (about 20% altogether) by media-hub-server and pulseaudio. This seems excessive and likely causes us to use quite a lot more power than we need.

The top of top looks like so:

  PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
 2773 phablet 20 0 342008 22344 15984 S 13,0 2,3 2:53.92 media-hub-serve
 2548 phablet 9 -11 368208 12028 8448 S 6,8 1,2 1:32.37 pulseaudio
16126 phablet 20 0 6284 1284 768 R 1,6 0,1 0:00.28 top
 2806 phablet 20 0 524540 110060 40520 S 1,3 11,2 0:51.24 unity8
 4991 phablet 20 0 389448 96144 30532 S 1,3 9,8 0:30.70 qmlscene

I suspect unity8/qmlscene are rendering playback progress unnecessarily when the screen is off, but media-hub-server and pulseaudio use about 20% CPU together.

dbus-monitor shows quite high activity every second:

method call sender=:1.136 -> dest=core.ubuntu.media.Service serial=13885 path=/core/ubuntu/media/Service/sessions/6; interface=org.freedesktop.DBus.Properties; member=Get
   string "org.mpris.MediaPlayer2.Player"
   string "Position"
method return sender=:1.51 -> dest=:1.136 reply_serial=13885
   variant int64 93624866996
method call sender=:1.136 -> dest=core.ubuntu.media.Service serial=13886 path=/core/ubuntu/media/Service/sessions/6; interface=org.freedesktop.DBus.Properties; member=Get
   string "org.mpris.MediaPlayer2.Player"
   string "Duration"
method return sender=:1.51 -> dest=:1.136 reply_serial=13886
   variant int64 306988000000
method call sender=:1.136 -> dest=core.ubuntu.media.Service serial=13887 path=/core/ubuntu/media/Service/sessions/6; interface=org.freedesktop.DBus.Properties; member=Get
   string "org.mpris.MediaPlayer2.Player"
   string "Position"
method return sender=:1.51 -> dest=:1.136 reply_serial=13887
   variant int64 93638280996
method call sender=:1.136 -> dest=core.ubuntu.media.Service serial=13888 path=/core/ubuntu/media/Service/sessions/6; interface=org.freedesktop.DBus.Properties; member=Get
   string "org.mpris.MediaPlayer2.Player"
   string "Duration"
method return sender=:1.51 -> dest=:1.136 reply_serial=13888
   variant int64 306988000000
method call sender=:1.136 -> dest=core.ubuntu.media.Service serial=13889 path=/core/ubuntu/media/Service/sessions/6; interface=org.freedesktop.DBus.Properties; member=Get
   string "org.mpris.MediaPlayer2.Player"
   string "Position"
method return sender=:1.51 -> dest=:1.136 reply_serial=13889
   variant int64 93653857996
method call sender=:1.136 -> dest=core.ubuntu.media.Service serial=13890 path=/core/ubuntu/media/Service/sessions/6; interface=org.freedesktop.DBus.Properties; member=Get
   string "org.mpris.MediaPlayer2.Player"
   string "Position"
method return sender=:1.51 -> dest=:1.136 reply_serial=13890
   variant int64 93657725996
method call sender=:1.136 -> dest=core.ubuntu.media.Service serial=13891 path=/core/ubuntu/media/Service/sessions/6; interface=org.freedesktop.DBus.Properties; member=Get
   string "org.mpris.MediaPlayer2.Player"
   string "Duration"
method return sender=:1.51 -> dest=:1.136 reply_serial=13891
   variant int64 306988000000
method call sender=:1.136 -> dest=core.ubuntu.media.Service serial=13892 path=/core/ubuntu/media/Service/sessions/6; interface=org.freedesktop.DBus.Properties; member=Get
   string "org.mpris.MediaPlayer2.Player"
   string "Position"
method return sender=:1.51 -> dest=:1.136 reply_serial=13892
   variant int64 93666179996
method call sender=:1.136 -> dest=core.ubuntu.media.Service serial=13893 path=/core/ubuntu/media/Service/sessions/6; interface=org.freedesktop.DBus.Properties; member=Get
   string "org.mpris.MediaPlayer2.Player"
   string "Duration"
method return sender=:1.51 -> dest=:1.136 reply_serial=13893
   variant int64 306988000000

:1.51 is pulseaudio, :1.136 is music app.

$ system-image-cli -i
current build number: 323
device name: krillin
channel: ubuntu-touch/rc-proposed/bq-aquaris.en
last update: 2016-05-01 13:37:17
version version: 323
version ubuntu: 20160429
version device: 20160329-a9bacdb
version custom: 20160324--36-54-vivid

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: media-hub 4.1.0+15.04.20160407.1-0ubuntu1 [origin: LP-PPA-ci-train-ppa-service-stable-phone-overlay]
Uname: Linux 3.4.67 armv7l
ApportVersion: 2.17.2-0ubuntu1.8
Architecture: armhf
Date: Tue May 3 11:25:19 2016
InstallationDate: Installed on 2016-04-29 (4 days ago)
InstallationMedia: Ubuntu 15.04 - armhf (20160429-020305)
SourcePackage: media-hub
UpgradeStatus: No upgrade log present (probably fresh install)

[Michał Sawicz (saviq)]

Bug #1475678 would likely reduce the qmlscene impact - as would making it use the new playlist APIs so we can remove it from lifecycle exceptions.