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: 2009-01-19
• Percentage of completion: 0%

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.

Our goals are to improve the existing tools where necessary and feasible 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.txt) and the libcgroups package.

Start the cgconfig service:

• Create the /etc/cgconfig.conf configuration file (the example is in the /samples section, the initscript from version 0.32.2 is able to create the mount point itself and mount the filesystem to it).
• For each mount point create the relevant directory and mount it. The filesystem type is cgroup, so an fstab line would look like this:

cgroup                   <mount-point>                cgroup  defaults        0 0

or you can mount it manually with this command:

mount -t cgroup cgroup <mount-point>

(see scripts/doc/howto.txt - this mentions that the script would mount it but this doesn't seem to work, probably a problem in the cgroup init script)

• Then you can start the service:

/sbin/service cgconfig start

Problems (in 0.32.2)

• Test example of cgconfig.conf from scripts/doc/howto.txt does not work.
• Changing /etc/cgconfig.conf while cgconfig is running leads to a bunch of error messages if you try to restart it.

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 administrate and monitor 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.

Comments and Discussion

• See Talk:Features/ControlGroups