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== Comment: #0 - Preeti U. Murthy <preeti.mur...@in.ibm.com> - 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: cgmanager (Ubuntu)
Importance: Undecided
Status: New
** Tags: architecture-ppc64le bot-comment bugnameltc-117800 severity-medium
targetmilestone-inin---
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mounts cgroups unconditionally which causes undesired effects with cpu hotplug
https://bugs.launchpad.net/bugs/1392176
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