debcrafters-packages team mailing list archive

Thread
Date

[Bug 1799265] Re: avahi-daemon high cpu, unusable networking

To: debcrafters-packages@xxxxxxxxxxxxxxxxxxx
From: Trent Lloyd <1799265@xxxxxxxxxxxxxxxxxx>
Date: Thu, 23 Oct 2025 04:41:29 -0000
Reply-to: Bug 1799265 <1799265@xxxxxxxxxxxxxxxxxx>
Sender: noreply@xxxxxxxxxxxxx

** Description changed:

Currently running Kubuntu 18.10, Dell XPS 13 9350

Since updating from Kubuntu 18.04 to 18.10, the avahi-daemon has been
consistently hampering network performance and using CPU for long
periods of time.

When booting machine from off state, avahi-daemon uses an entire CPU at
max load for approx 10 minutes. During this time, internet connectivity
via wifi is essentially unusable. The wifi connection is good, but it
seems that http transactions are cutoff mid-way so no webpage is able to
load.

When waking from sleep, the avahi-daemon causes similar symptoms, but
with less than 1 full cpu usage, and with somewhat less degraded network
performance, but still quite unusable.

I have never had issues with avahi prior to the 18.10 upgrade, so I am
fairly confident the issue is rooted in that change.

ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: avahi-daemon 0.7-4ubuntu2
ProcVersionSignature: Ubuntu 4.18.0-10.11-generic 4.18.12
Uname: Linux 4.18.0-10-generic x86_64
ApportVersion: 2.20.10-0ubuntu13
Architecture: amd64
CurrentDesktop: KDE
Date: Mon Oct 22 10:00:34 2018
InstallationDate: Installed on 2017-07-24 (455 days ago)
InstallationMedia: Ubuntu 17.04 "Zesty Zapus" - Release amd64 (20170412)
ProcEnviron:
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
LD_PRELOAD=<set>
SHELL=/bin/bash
SourcePackage: avahi
UpgradeStatus: Upgraded to cosmic on 2018-10-20 (2 days ago)

[ Impact ]

* avahi-daemon consumes a large amount of CPU over time, particularly
on laptop/desktop use cases. Many reports of it burning 100% CPU.

* This also leads to increased multicast traffic which has been
observed to cause high packet loss on WiFi networks at very large events
with many Ubuntu laptops on the same network.

* This issue was fixed long ago fixed upstream, in Debian and in
Kinetic+ but not previously backported to Jammy.

[ Test Plan ]

- * It is not easy to reproduce the issue on demand, it tends to happen
- at random, only on busy networks possibly after many days or more of
- uptime. I don't currently have a way to easily reproduce the issue for
- SRU verification.
+ The problem with this bug is that when a watch is cleaned up, it stops
+ timeouts being cleaned up. The list of timeouts then grows and when
+ iterated causes high CPU usage.

- * Upstream bug/diagnosis: https://bugs-devel.debian.org/cgi-
- bin/bugreport.cgi?bug=993051
+ Watches are created when nss-mdns connects via the simple socket, so we
+ can trigger this with an DNS lookup for a .local host: getent hosts
+ avahitest1.local

- * TODO: Add basic manual functional test plan
+ Timeouts are created when a DBus client disconnects, so we can trigger
+ this by calling avahi-browse -a -t which will print out all services and
+ then terminate the client.
+
+ 1. Launch two test VMs, avahitest1 and avahitest2. Install avahi-utils,
+ avahi-daemon, libnss-mdns and sysstat. Upgrade to the fix on one of them
+ only.
+
+ 2. Launch mpstat 15 on both hosts
+
+ 3. Launch many parallel avahi-browse on both: yes | xargs -n1 -I{} -P20
+ avahi-browse -a -t
+
+ 4. Launch many DNS lookups on both:
+ while true; do getent hosts avahitest2.local; sleep 0.1; done
+
+ 5. Observe over time the CPU usage of one VM slowly grows, while the
+ other does not.

[ Where problems could occur ]

* This patch is a single line change for a missing cleanup, that has
shipped in Kinetic+ for several years

* The version shipping in those releases is substantially similar to
the current release (no new upstream release)

- * However: avahi-daemon is a default installed package on Desktops, so
- there is a high potential impact
+ * However: avahi-daemon is a default package on Desktops, so there is a
+ high potential impact

[ Other Info ]

- * Upstream commit: https://github.com/avahi/avahi/pull/366
- * Originally diagnosed/resolved in the Debian bug: https://bugs.launchpad.net/ubuntu/+source/avahi/+bug/1799265
- * This patch ships in later versions (even the current version), however I renamed the patch to prefix the LP bug number per the preferences, and added DEP3 headers.
+ * Originally diagnosed/resolved in the Debian bug:
+ https://bugs-devel.debian.org/cgi-bin/bugreport.cgi?bug=993051
+
+ * Upstream PR: https://github.com/avahi/avahi/pull/366
+
+ * This patch ships in later versions (even the current version),
+ however I renamed the patch to prefix the LP bug number per the
+ preferences, and added DEP3 headers.

--
You received this bug notification because you are a member of
Debcrafters packages, which is subscribed to avahi in Ubuntu.
https://bugs.launchpad.net/bugs/1799265

Title:
avahi-daemon high cpu, unusable networking

Status in Avahi:
New
Status in avahi package in Ubuntu:
Fix Released
Status in avahi source package in Jammy:
Confirmed
Status in avahi source package in Noble:
Fix Released

Bug description:
Currently running Kubuntu 18.10, Dell XPS 13 9350

Since updating from Kubuntu 18.04 to 18.10, the avahi-daemon has been
consistently hampering network performance and using CPU for long
periods of time.

When booting machine from off state, avahi-daemon uses an entire CPU
at max load for approx 10 minutes. During this time, internet
connectivity via wifi is essentially unusable. The wifi connection is
good, but it seems that http transactions are cutoff mid-way so no
webpage is able to load.

When waking from sleep, the avahi-daemon causes similar symptoms, but
with less than 1 full cpu usage, and with somewhat less degraded
network performance, but still quite unusable.

I have never had issues with avahi prior to the 18.10 upgrade, so I am
fairly confident the issue is rooted in that change.

[ Impact ]

* avahi-daemon consumes a large amount of CPU over time, particularly
on laptop/desktop use cases. Many reports of it burning 100% CPU.

* This also leads to increased multicast traffic which has been
observed to cause high packet loss on WiFi networks at very large
events with many Ubuntu laptops on the same network.

* This issue was fixed long ago fixed upstream, in Debian and in
Kinetic+ but not previously backported to Jammy.

[ Test Plan ]

The problem with this bug is that when a watch is cleaned up, it stops
timeouts being cleaned up. The list of timeouts then grows and when
iterated causes high CPU usage.

Watches are created when nss-mdns connects via the simple socket, so
we can trigger this with an DNS lookup for a .local host: getent hosts
avahitest1.local

Timeouts are created when a DBus client disconnects, so we can trigger
this by calling avahi-browse -a -t which will print out all services
and then terminate the client.

1. Launch two test VMs, avahitest1 and avahitest2. Install avahi-
utils, avahi-daemon, libnss-mdns and sysstat. Upgrade to the fix on
one of them only.

2. Launch mpstat 15 on both hosts

3. Launch many parallel avahi-browse on both: yes | xargs -n1 -I{}
-P20 avahi-browse -a -t

4. Launch many DNS lookups on both:
while true; do getent hosts avahitest2.local; sleep 0.1; done

5. Observe over time the CPU usage of one VM slowly grows, while the
other does not.

[ Where problems could occur ]

* This patch is a single line change for a missing cleanup, that has
shipped in Kinetic+ for several years

* The version shipping in those releases is substantially similar to
the current release (no new upstream release)

* However: avahi-daemon is a default package on Desktops, so there is
a high potential impact

[ Other Info ]

* Originally diagnosed/resolved in the Debian bug:
https://bugs-devel.debian.org/cgi-bin/bugreport.cgi?bug=993051

* Upstream PR: https://github.com/avahi/avahi/pull/366

* This patch ships in later versions (even the current version),
however I renamed the patch to prefix the LP bug number per the
preferences, and added DEP3 headers.

To manage notifications about this bug go to:
https://bugs.launchpad.net/avahi/+bug/1799265/+subscriptions