[Bug 2003027] Re: fq_codel qdisc compiled but not enabled on 22.10

[Launchpad Bug Tracker]

This bug was fixed in the package procps - 2:4.0.4-4ubuntu4

---------------
procps (2:4.0.4-4ubuntu4) oracular; urgency=medium

  * d/sysctl.d/10-bufferbloat.conf: set default qdisc to fq_codel (LP:
#2003027)

 -- Heitor Alves de Siqueira <halves at canonical.com>  Wed, 17 Jul 2024
14:59:18 +0000

** Changed in: procps (Ubuntu Oracular)
       Status: Fix Committed => Fix Released

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Title:
  fq_codel qdisc compiled but not enabled on 22.10

Status in Ubuntu:
  Fix Committed
Status in procps package in Ubuntu:
  Fix Released
Status in The Noble Numbat:
  Confirmed
Status in procps source package in Noble:
  In Progress
Status in The Oracular Oriole:
  Fix Committed
Status in procps source package in Oracular:
  Fix Released

Bug description:
  [ Impact ]
  Starting with Ubuntu 22.10, the default qdisc regressed to pfifo_fast. This is due to a change we merged from Debian, removing systemd's /usr/lib/50-default.conf file. pfifo_fast does not prevent bufferbloat issues, severely degrading networking performance on Ubuntu systems.

  [ Test Plan ]
  On an Ubuntu VM, check that net.core.default_qdisc is set to 'fq_codel'. `tc qdisc show` should also confirm fq_codel is being used.

  halves at noble-vm:~$ sysctl net.core.default_qdisc
  net.core.default_qdisc = fq_codel

  halves at noble-vm:~$ tc qdisc show
  qdisc noqueue 0: dev lo root refcnt 2
  qdisc mq 0: dev enp5s0 root
  qdisc fq_codel 0: dev enp5s0 parent :1 limit 10240p flows 1024 quantum 1514 target 5ms interval 100ms memory_limit 32Mb ecn drop_batch 64

  [ Where Problems Could Occur ]
  Users relying on the default pfifo_fast qdisc could see different networking behavior.

  [ Other Info ]
  Instead of adding a sysctl.conf file, Debian has decided to change their default kernel configs to use fq_codel. This has the disadvantage of being "hidden" from end users, instead of being a queryable setting in e.g. /etc/sysctl.d/, and all kernel documentation still refers to pfifo_fast as being the default.

  Systemd's /usr/lib/50-default.conf file includes a lot of other
  settings that are either overruled elsewhere (e.g. from procps) or are
  entirely missing from our stable releases. Introducing a diff from
  Debian to ship this file only for the net.core.default_qdisc changes
  seems excessive, so having a dedicated place under procps where other
  similar toggles are already present seems like the more appropriate
  solution.

  --
  [ Original Description ]
  fq_codel has been the default in ubuntu since #1436945

  It is also now the default in debian. Somewhere between 22.04 and
  22.10 though, it stopped being enabled by systemd? (it used to be
  enabled there via a sysctl), and thus 22.10 (I tried both ubuntu
  server and ubuntu studio) doesn't have it on. I rather *immediately*
  noticed this huge regression (I run my ethernet at 100Mbit, and thus
  immediately saw 400+ms latency) - and I hope it can be fixed in the
  next release?

  it can also be made the default via compiling it into the kernel as a
  kernel default.

  Aggh! death to fifos!

  root at localhost:~# sysctl -a | grep qdisc
  net.core.default_qdisc = pfifo_fast

  disc pfifo_fast 0: dev eth0 parent :1 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
   Sent 5250 bytes 53 pkt (dropped 0, overlimits 0 requeues 0)
   backlog 0b 0p requeues 0

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