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[Bug 1480877] Re: Access points' "PropertiesChanged" dbus signals freeze UI on mobile devices


One of the frustrating parts about this bug is the incomplete
description, and the fact that it's been nigh impossible to nail down a
set of concrete steps to reproduce...

Also, the bug description contends that NM 'PropertiesChanged' signals
are causing the UI freezes, however we have no idea why...

We haven't been thinking enough about what's listening for the signals.
"If a tree falls in the woods and nobody hears it?"  The more listeners
for a particular DBus message, the more work the daemon has to due ( and
the more context switches involved ).

Also, Mike Terry had mentioned in one of this comments that he'd seen
the dbus daemon was spending most of it's time in it's match rules
logic.   Turns out that a new method had been added by upstream to the
dbus Stats interface called 'GetAllMatchRules'.   I'd been interested in
this, for awhile, but finally got time to work on it.

Two other points before I dive into the match rules:

As of the latest rc-proposed for krillin ( # ), when the WiFi is enabled
and the HERE app, Nearby scope, or Today scope are displayed, the
location services increases the rate of WiFi scanning to once every
12-15s ( usually it's around 2m if connected to an AP ).  When I decided
to look at the incoming traffic to NM, I noticed that everytime a scan
occurs, three different processes all seem to query the same set of NM
AccessPoint objects.  The clients all use 'Get' instead of 'GetAll' for
the properties, and again it looks like each process is generating the
same set of method requests.  The processes in question are:

 - posclientd
 - slpgwd
 - ubuntu-location-serviced

The amount of traffic isn't a huge impact, but it could be made more

Back to the who's listening to the signals approach...

First, I got lucky and was able to run dbus 1.10.0-1ubuntu1 from wily on
my krillin on first try.  This krillin was freshly flashed to the latest
rc-proposed ( #162 ).

When I ran the example get-all-match.py script ( see attached ) for the
system bus ( use sudo and specify --system ), I was blown away that the
same three location services processes previously mentioned above, each
had 512 match rules for NM defined!  509 of the 512 were also flagged as
warnings as no signal name was specified.   It looks like these location
processes are adding watches ( sometimes duplicates ) for every single
AccessPoint object that ever gets created by NM.  It also looks like
these watches are never being cleaned up.

So... I tried the same experiment on a mako, also freshly flashed ( rc-
proposed, #150 ).   Turns out I got lucky with krillin, mako didn't like
the new dbus, and wouldn't boot into the UI.  I had re-flash, then
backport the changes to the version in vivid ( 1.8 ).   This verions (
~awe3 ) is available in my PPA:


When I ran this version on mako, the first thing I noticed was that the
match rule counts were much lower at first.   As I didn't have
apps/scopes to drive the increased WiFi scanning, I triggered extra
scans by hand and watched the match rule counts ...and they slowly
started to grow!  After an hour or so, they actually exceeded 512 rules
per process!

It turns out the dbus configuration of the system bus in vivid was
changed to allow up to *5000* match rules per process.  See the attached
patch for bug #454093.  As I'm wrapping up this comment, each process is
just about to hit 1000 rules each ( after 3h of uptime ).

I tried toggling WiFi on/off/on, but this doesn't seem to effect the
number of match rules involved.

Tomorrow, I will try and reproduce the hangs by using the backport
version of dbus from my PPA on krillin and let it run all day.

One last note, it'd be good to confirm that fully stopping these
location service processes makes the problem go away.  That said, I
wasn't able to find an easy way to get the processes involved to shut
down.  Disabling from the indicator doesn't do it, and stopping the
system upstart job ( 'sudo stop ubuntu-location-service' ) didn't do so

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  Access points' "PropertiesChanged" dbus signals freeze UI on mobile

Status in Canonical System Image:
Status in indicator-network package in Ubuntu:
Status in network-manager package in Ubuntu:
Status in network-manager package in Ubuntu RTM:

Bug description:
  Krillin, rc-proposed, r83

  I've been trying to track down the cause of the occasional UI freezes on my Krillin device, and I noticed that whenever the UI freezes for 2-4 seconds, I get a burst of "PropertiesChanged" signals in dbus-monitor

  Here's a log of what's shown in dbus-monitor:

  I'd guess the problem is in the code that actually catches the signals
  and acts accordingly.

  1) Move to a place where many wifi hotspots are available
  2) Connect the device via USB and run "phablet-shell" and then "dbus-monitor"
  3) Use the device while keeping an eye on dbus-monitor output

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