Features/ControlGroups

Summary

Improve the existing tools where necessary and feasible and/or to create new ones e.g. to create or modify persistent cgroups configuration or display control groups data (using libcgroups package).

Owner

• Nils Philippsen
  • email: nphilipp@redhat.com
• Ivana Varekova
  • email: varekova@redhat.com
• Jan Šafránek
  • email: jsafrane@redhat.com

Current status

• Targeted release:
• Last updated: 2009-02-10
• Percentage of completion: 20%

Detailed Description

Since kernel 2.6.24, Linux has so called control groups as a means to partition available resources between running processes. Libcgroups makes that functionality available to programmers and contains two tools, cgexec and cgclassify, to start processes in a control group or move existing processes from one control group to another.

In fedora there already is a package libcgroups.

• The goal for Fedora11 is:

to improve this package where necessary (bugfixing, add/fix documentation/man-pages, add examples, fix error handling, rework logging, ...) and/or to create displaying tool and a tool which enable user to start a service in given context group.

• The longterm goal is:

to improve this package where necessary and/or to create new ones e.g. to create or modify persistent cgroups configuration display control groups data. At the beginning the focus will be on command line tools, but we'll keep in mind that in the long term we'll likely want to have graphical tools. These would offer similar functionality and we should try to make sure that any non-UI code written is usable from both kinds of frontends. First steps would include bugfixing and creation of missing tools, then creation of Python bindings to use from any GUI tools.

Benefit to Fedora

Libcgroups handles the new kernel features which are able to restrict the sources for tasks. This project should help the user to make the best of this feature.

Scope

• Required extended testing and fixing of libcgroups package and in time when libcgroups will be stable enough try to add start to write another parts - based on existing ones.

How To Test

For now it is necessary to have a kernel with cgroups support (Documentation/cgroups/cgroups.txt) and the libcgroup package.

1. yum install libcgroup

• creating cgroups -

1. one configure /etc/cgconfig.conf file
2. two start/stop cgconfig service and test whether the created groups are as expected

• moving task to groups -

1. one with configured cgroups - using the previsou steps configure /etc/cgrules.conf file
2. two start/stop new proces using cgexec
3. three test cgrulesengd daemon (should automatically moved processes via cgrules.conf configure file)
4. four configure pam module and test that works if you login

User Experience

Currently, the libcgroups package has several bugs, these will have to be fixed at first. When that is out of the way, configuration (or even monitoring) tools would reduce the barrier of entry to using control groups on Linux significantly.

Dependencies

• Depends on kernel > 2.6.24 and libcgroups (current version is 0.32.2) which both are in Fedora since F-9.

Contingency Plan

Currently, nothing depends on libcgroup or the tools which would use it. If things go really wrong, we can always go back to the last working version of libcgroup.

Documentation

• kernel documentation:
  • Documentation/cgroups
  • Documentation/scheduler/sched-rt-group.txt
  • Documentation/scheduler/sched-design-CFS.txt:
• Documentation/cgroups/]
• libcg:
  • upstream site
  • LWN.net article: libcg: design and plans

Release Notes

libcgroups is a tool which helps to manipulate, control and administrate control groups and the associated controllers. Using this tool it is possible to aggregate/partition set of tasks and their future children into hierarchical groups with specialized access to resources.

The tool consists of two parts -

• The first enable user to create persistent cgroups configuration using a configure file and a service which parse this configuration.

• The second part enable user to define to which group belong the given process/given processes. This divison is based on uid or gid of processes. The user can start a service which will put the processes to the right subsystem, or there is a tool to move the process to the right subsystem or to create the process in it. There is also pam modul which have this functionality.

Comments and Discussion

• See Talk:Features/ControlGroups