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

[Christian Ehrhardt ]

Hi Ethanay
> All I can find is a recommendation not to use it on CPUs with 2 or fewer
> cores as the overhead is said to be too high

This isn't a real problem anyway, the service will stop immediately if only
running on one core - even if running on multiple cores with the same
cache (as the intended benefit is due to cache hotness by having all I/O
hitting the same cache).

> I can imagine it might still add undesirable or even critical latency in
> applications that are highly latency sensitive

I understand your line of thought, but it might even improve latency.
If there is no bottleneck on the cores assigned to handle an IRQ then
the improved cache hit rate will make even latency better.
And if there is a strong bottleneck, then some drivers without IRQbalance
would end up locked on one cpu - so again these might gain lower latency.
But I have no data on this either (just like no one seems to have on almost
any of this).

Just like others I'd personally more expect the drawback to be on a potential
lack of power saving.

> This website gave me some clarity on the theory and purpose:
> https://www.baeldung.com/linux/irqbalance-modern-hardware

Hah, didn't find this one yet - thank you!
But to me it only underlines the "it can help as much or even more often"
expectation.

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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:
  Confirmed
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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