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[Takashi Kajinami <1937261@xxxxxxxxxxxxxxxxxx>]

This is a problem with python-msgpack in Ubuntu, and does not look like
a bug in oslo.privsep or neutron.

** No longer affects: oslo.privsep

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https://bugs.launchpad.net/bugs/1937261

Title:
  python3-msgpack package broken due to outdated cython

Status in Ubuntu Cloud Archive:
  Invalid
Status in Ubuntu Cloud Archive ussuri series:
  Fix Released
Status in neutron:
  New

Bug description:
  After a successful upgrade of the control-plance from Train -> Ussuri
  on Ubuntu Bionic, we upgraded a first compute / network node and
  immediately ran into issues with Neutron:

  We noticed that Neutron is extremely slow in setting up and wiring the
  network ports, so slow it would never finish and throw all sorts of
  errors (RabbitMQ connection timeouts, full sync required, ...)

  We were now able to reproduce the error on our Ussuri DEV cloud as
  well:

  1) First we used strace -ffff -p $PID_OF_NEUTRON_LINUXBRIDGE_AGENT and noticed that the data exchange on the unix socket between the rootwrap-daemon and the main process is really really slow.
  One could actually read line by line the read calls to the fd of the socket.

  2) We then (after adding lots of log lines and other intensive manual
  debugging) used py-spy (https://github.com/benfred/py-spy) via "py-spy
  top --pid $PID" on the running neutron-linuxbridge-agent process and
  noticed all the CPU time (process was at 100% most of the time) was
  spent in msgpack/fallback.py

  3) Since the issue was not observed in TRAIN we compared the msgpack
  version used and noticed that TRAIN was using version 0.5.6 while
  Ussuri upgraded this dependency to 0.6.2.

  4) We then downgraded to version 0.5.6 of msgpack (ignoring the actual
  dependencies)

  --- cut ---
  apt policy python3-msgpack
  python3-msgpack:
    Installed: 0.6.2-1~cloud0
    Candidate: 0.6.2-1~cloud0
    Version table:
   *** 0.6.2-1~cloud0 500
          500 http://ubuntu-cloud.archive.canonical.com/ubuntu bionic-updates/ussuri/main amd64 Packages
       0.5.6-1 500
          500 http://de.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
          100 /var/lib/dpkg/status
  --- cut ---

  
  vs.

  --- cut ---
  apt policy python3-msgpack
  python3-msgpack:
    Installed: 0.5.6-1
    Candidate: 0.6.2-1~cloud0
    Version table:
       0.6.2-1~cloud0 500
          500 http://ubuntu-cloud.archive.canonical.com/ubuntu bionic-updates/ussuri/main amd64 Packages
   *** 0.5.6-1 500
          500 http://de.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
          100 /var/lib/dpkg/status
  --- cut ---

  
  and et voila: The Neutron-Linuxbridge-Agent worked just like before (building one port every few seconds) and all network ports eventually converged to ACTIVE.

  I could not yet spot which commit of msgpack changes
  (https://github.com/msgpack/msgpack-python/compare/0.5.6...v0.6.2)
  might have caused this issue, but I am really certain that this is a
  major issue for Ussuri on Ubuntu Bionic.

  There are "similar" issues with
   * https://bugs.launchpad.net/oslo.privsep/+bug/1844822
   * https://bugs.launchpad.net/oslo.privsep/+bug/1896734

  both related to msgpack or the size of messages exchanged.

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