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

[Dave Taht]

elsewhere bql has been entering the virtio-net driver.

---------- Forwarded message ---------
From: Heitor Alves de Siqueira <2003027 at bugs.launchpad.net>
Date: Wed, Jul 17, 2024 at 11:05 AM
Subject: [Bug 2003027] Re: fq_codel qdisc compiled but not enabled on 22.10
To: <dave.taht at gmail.com>


** Description changed:

+ [ 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
+  Sent 5250 bytes 53 pkt (dropped 0, overlimits 0 requeues 0)
+  backlog 0b 0p requeues 0

-- 
You received this bug notification because you are subscribed to the bug
report.
https://bugs.launchpad.net/bugs/2003027

Title:
  fq_codel qdisc compiled but not enabled on 22.10

Status in Ubuntu:
  Confirmed

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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-- 
Artists/Musician Campout Aug 9-11
https://www.eventbrite.com/e/healing-arts-event-tickets-928910826287
Dave Täht CSO, LibreQos
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