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[Bug 1392176] Comment bridged from LTC Bugzilla


------- Comment From shgwei@xxxxxxxxxx 2016-06-18 09:49 EDT-------
(In reply to comment #77)
> "LXC cases, like docker and KVM" - did you mean non-lxc cases?
> xenial by default should now be using libpam-cgfs, should not be using
> cgmanager, and should not be creating cpusets.

Thanks for the info. However what I cares is the docker/KVM case. For
example, when I created docker on xenial 16.04, the container process
will still be added into /sys/fs/cgroup/cpuset/docker; When creating
KVM, the KVM process will be added into sub cpuset cgroup as well. As a
result, the issue can still impact those tasks.

For the above, is it already covered(on higher xenial version) or does
it need more consideration?

- Simon

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  mounts cgroups unconditionally which causes undesired effects with cpu

Status in cgmanager package in Ubuntu:
  Fix Released
Status in linux package in Ubuntu:
  Fix Released
Status in systemd package in Ubuntu:
  Fix Released

Bug description:
  == Comment: #0 - Preeti U. Murthy <preeti.murthy@xxxxxxxxxx> - 2014-10-20 04:40:12 ==
  ---Problem Description---
  Systemd mounts cgroups explicitly every boot. Since the user had no say in it, undesired consequences are observed in reaction to cpu hotplug operations.  Here is how.

  Systemd moves the tasks to the cgroup mounted by it. This cgroup automatically becomes the child of the root cgroup which is present by default. The children cgroups are not expected to remember their configured cpusets after hotplug operations in the kernel. Hence when cpus are taken offline and brought back online they are no longer used for load balancing of tasks and hence remain unused. 
     This is an undesired consequence because the user had not even asked for cgroups to be mounted, yet is not able to use the full capacity of the system.

  Only when the user himself creates cgroup hierarchies, should he be
  exposed to the side effects of cpu hotplug on cpusets. Else all online
  cpus must be made available to him which is not happening since
  systemd mounts cgroups on every boot.

  Hence please revert this feature or provide an explaination as to why this is being done.
  ---uname output---
  Linux tul181p1 3.16.0-18-generic #25-Ubuntu SMP Fri Sep 26 02:39:53 UTC 2014 ppc64le ppc64le ppc64le GNU/Linux
  Machine Type = Tuleta 8286-42A 
  A debugger was configured, however the system did not enter into the debugger
  ---Steps to Reproduce---
   $ taskset -p $$
  $ 0-127
  $ echo 0 > /sys/devices/system/cpu/cpu7/online
  $ taskset -p $$
  $ 0-6,8-127
  $ echo 1 > /sys/devices/system/cpu/cpu7/online
  $ taskset -p $$
  $ 0-6,8-127
  Userspace tool common name: systemd 
  The userspace tool has the following bit modes: 64-bit 

  Userspace rpm: systemd_208-8ubuntu8_ppc64el.deb

  Userspace tool obtained from project website:   208-8ubuntu8

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