[Bug 1833322] Re: Consider removing irqbalance from default install on desktop images

[Steve Langasek]

Hi Christian,

I see a lot of strong opinions being given, but aside from the "don't
use it in KVM" guidance which appears to be based on GCE's engineering
expertise, very little evidence that irqbalance is actually a problem.

I think it's true that in the default config, irqbalance can interfere
with putting CPUs into higher C states to conserve power.  However, I
don't see any indication of quantitative analysis showing the impact.

Recent versions of irqbalance have a '--powerthresh' argument that can
be used to tell irqbalance to rebalance across fewer cores when CPU load
is low, to allow some of the cores to be put into a sleep state and
conserve power.  My own initial testing on my desktop shows that this
gets used for all of about 10 seconds at a time every few hours, before
the load increases and irqbalance wakes the core back up...

I would want any decision to remove irqbalance from the desktop to be
based on evidence, not conjecture.  At a minimum, I think what I would
like to see is output from powertop showing both power consumption and
CPU idle stats over a reasonable amount of time (10 minutes?), on a
representative client machine, for a 2x3 matrix of configurations:

 - idle vs normal desktop load
 - irqbalance disabled vs irqbalance enabled with defaults vs irqbalance enabled with IRQBALANCE_ARGS=--powerthresh=1

System should be rebooted between each of the irqbalance configurations,
as I'm not sure what does or doesn't persist in the CPU config after
irqbalance exits.

I am specifically not going to try to rebut the various webpages
referenced here, beyond saying that there's an awful lot of these pages
pointing to one other as authoritative sources on irqbalance without
there actually being evidence to back them up (and a heaping spoonful of
misinformation / outdated information along the way).  So if we're going
to make a change, there should be due diligence to demonstrate a
benefit, it should not be based on Internet hype.

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https://bugs.launchpad.net/bugs/1833322

Title:
  Consider removing irqbalance from default install on desktop images

Status in irqbalance package in Ubuntu:
  New
Status in ubuntu-meta package in Ubuntu:
  Confirmed

Bug description:
  as per https://github.com/pop-os/default-settings/issues/60

  Distribution (run cat /etc/os-release):

  $ cat /etc/os-release
  NAME="Pop!_OS"
  VERSION="19.04"
  ID=ubuntu
  ID_LIKE=debian
  PRETTY_NAME="Pop!_OS 19.04"
  VERSION_ID="19.04"
  HOME_URL="https://system76.com/pop"
  SUPPORT_URL="http://support.system76.com"
  BUG_REPORT_URL="https://github.com/pop-os/pop/issues"
  PRIVACY_POLICY_URL="https://system76.com/privacy"
  VERSION_CODENAME=disco
  UBUNTU_CODENAME=disco

  Related Application and/or Package Version (run apt policy $PACKAGE
  NAME):

  $ apt policy irqbalance
  irqbalance:
  Installed: 1.5.0-3ubuntu1
  Candidate: 1.5.0-3ubuntu1
  Version table:
  *** 1.5.0-3ubuntu1 500
  500 http://us.archive.ubuntu.com/ubuntu disco/main amd64 Packages
  100 /var/lib/dpkg/status

  $ apt rdepends irqbalance
  irqbalance
  Reverse Depends:
  Recommends: ubuntu-standard
  gce-compute-image-packages

  Issue/Bug Description:

  as per konkor/cpufreq#48 and
  http://konkor.github.io/cpufreq/faq/#irqbalance-detected

  irqbalance is technically not needed on desktop systems (supposedly it
  is mainly for servers), and may actually reduce performance and power
  savings. It appears to provide benefits only to server environments
  that have relatively-constant loading. If it is truly a server-
  oriented package, then it shouldn't be installed by default on a
  desktop/laptop system and shouldn't be included in desktop OS images.

  Steps to reproduce (if you know):

  This is potentially an issue with all default installs.

  Expected behavior:

  n/a

  Other Notes:

  I can safely remove it via "sudo apt purge irqbalance" without any
  apparent adverse side-effects. If someone is running a situation where
  they need it, then they always have the option of installing it from
  the repositories.

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