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 with aforementioned tools, but the overall quality is very poor. There is almost no documentation, no man pages, no configuration file samples.

The goal for Fedora 11 is to improve this package where necessary, i.e.:

• bugfixing
• add/fix documentation and man-pages
• add examples
• fix error handling
• rework logging
• create displaying tool (to see, in which control group is given process)
• prepare a way, how to start a service daemon in given context group

The long term goal is to create new tools to e.g. create or modify persistent cgroups configuration and 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.

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. The user/tester must know, what cgroups are and what they are good for, the best is to read aforementioned kernel doc.

1. yum install libcgroup

• Creating cgroups:

1. Configure /etc/cgconfig.conf file - there should be nice example and man page packaged.
2. Start/stop cgconfig service and test whether the created groups are as expected.

• Moving task to groups:

1. Prepare some cgroups, i.e. prepare /etc/cgconfig.conf and start cgconfig service.
2. Start/stop new proces using cgexec and check that it's in appropriate cgroup.
3. Prepare cgrules.conf file - there should be some sample and man page available.
4. Test cgrulesengd daemon (it should automatically move processes as written in cgrules.conf).
5. Configure cgroup pam module and test that works if a user logs in (again, driven by cgrules.conf).

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 one enables user to create persistent cgroups configuration using a configuration file and a service which creates configured groups on startup.

• The second part enables 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.

Comments and Discussion

• See Talk:Features/ControlGroups