kernel-packages team mailing list archive

[Serge Hallyn <1392176@xxxxxxxxxxxxxxxxxx>]

Quoting Martin Pitt (martin.pitt@xxxxxxxxxx):
> > Note that when i start up a vivid vm without cgmanager installed, cpuset is still mounted and login sessions get a cpuset cgroup:
> > 2:cpuset:/user.slice/user-1000.slice/session-1.scope
> 
> Note that this is by request of Stèphane, it's an ubuntu specific patch
> to make user LXC containers work under systemd. I didn't follow the
> discussion here in depth and I don't know much about the cgroup
> internals -- I just wanted to say let me know if the above is unintended
> and systemd should stop configuring the cpuset controller for user
> sessions (then user LXC would need to get some adjustments for that too,
> though)

Cpusets are not *required* for lxc.  Perhaps we should in fact default
to only providing name=systemd, devices and freezer cgroups for users?
We'd want to very widely advertise how to enable other cgroups.

Currently lxc would fail this way, but we could teach it to ignore
inability to create cgroups which aren't required.  (This isn't as
simple as it seems, since using the keyword "all" for controllers
would no longer work, but it's doable)

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https://bugs.launchpad.net/bugs/1392176

Title:
  mounts cgroups unconditionally which causes undesired effects with cpu
  hotplug

Status in cgmanager package in Ubuntu:
  Confirmed
Status in linux package in Ubuntu:
  Confirmed
Status in systemd package in Ubuntu:
  New

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 
   ---Debugger---
  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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