[Bug 1833322] Re: Please consider no more having irqbalance enabled by default (per image/use-case/TBD)

[Henry Wertz]

Just for perspective on this, I've used Linux since about 1993
(originally Slackware, then Gentoo, then Ubuntu) and recall manually
adding irqtune to my system in the distant past.

When irqtune was originally developed, it was common to run XT-PIC, all
interrupts were went to CPU 0, period.  When one turned on IO-APIC back
then, interrupts still went to CPU 0 by default but could be rerouted.
This was largely to be able to hit gigabit+ speeds on systems of the
time.

Now?   CPUs are faster, memory is faster, and the interrupt handlers are
much more efficient than in the kernel of, say, 15 or 20 years ago.  If
you disable irqtune, you can observe in /proc/interrupts that various
device interrupts are still sent to CPUs other than CPU0, they just
don't go ping-ponging around between all of them like they do with
irqtune.  A big difference compared to the early days, for example for
ethernet a lot of the work that was done in the interrupt handler back
then, the interrupt handler now does the bare minimum and does the rest
of the work with a kernel thread (same for wifi, which tends to be a bit
of an interrupt and CPU hog).  Meaning the actual interrupts take much
less time to run now than they did then.  The total CPU time could still
add up to more than 1 core can handle if you had, say, 10gbps ethernet
(or 1gbps ethernet or wifi on a slower CPU).  But the kernel threads can
be scheduled to any CPU core just like any other thread even if the
interrupts are tied to one CPU..

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

Title:
  Please consider no more having irqbalance enabled by default (per
  image/use-case/TBD)

Status in Ubuntu on IBM z Systems:
  Confirmed
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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