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== 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

** Affects: systemd (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: architecture-ppc64le bot-comment bugnameltc-117800 severity-medium targetmilestone-inin---
-- 
Systemd mounts cgroups unconditionally which causes undesired effects with cpu hotplug
https://bugs.launchpad.net/bugs/1392176
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