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Effective Linux Resource Management

Use control groups to manage complexity and performance in SUSE Linux Enterprise systems

Written by Matthias G. Eckermann and Bill Tobey

Cset: An Easy Approach to Control Groups

Managing control groups manually—mounting the virtual file systems, creating the cgroup hierarchy, starting new processes in the appropriate groups, moving existing processes into or between groups, tracking group membership, then closing down unneeded groups—can become confusing and complex. Fortunately for Novell customers who want a simpler point of entry, there is a Novell-developed tool, first introduced in SUSE Linux Enterprise, that greatly simplifies cgroup implementation and management.

The cpuset management utility is a Python application that provides an easy-to-use command line interface for the cpusets functionality in the Linux kernel. Called cset after installation (yes, it’s admittedly a little confusing) the tool addresses only the CPU and memory partitioning functionality of the cpuset subsystem. But since these are the obvious starting points for resource management and performance optimization, the cset tool offers an ideal way to sample the power and potential of control groups.

Preparing to Use Cgroups

To prepare a system for performance optimization with control groups, begin with a patched SUSE Linux Enterprise 11 SP 1 install, then add the following packages:

  • Libcgroup1 – The library for controlling and monitoring cgroups
  • Libcpuset1 – A library that provides a convenient 'C' API to the CPUset subsystem
  • Kernel-source – The source code for the Linux kernel
  • Cpuset – The cpuset management utility
  • Stress – A simple workload generator for testing the impact of our process grouping and resource allocation measures on application and system performance. Available through the opensuse build service at: http://software.opensuse.org/.
  • Lxc - Linux containers (optional). We’ll talk a little more about this important new development at the end of this article.

Simple Cgroups with Cpuset

The cpuset (cset) utility makes it quite easy to execute the basic tasks of control group setup and management.

Step One: Discover the available CPU and memory resources on your system. Use the set command as follows:

- cset set --list

to create a list of the available resources.

Step Two: Create the CPUSET hierarchy. In the simplest configuration there are at least three cpusets. The root cpuset which contains all CPU and memory nodes, the system cpuset which is assigned cpu and memory resources for lower-priority system tasks, and at least one user cpuset which receives sufficient resources to ensure adequate performance of higher-priority user tasks.

Assuming we have a four-way NUMA machine, the command:

- cset set --cpu=2-4--mem=1 --set=Charlie

will create a user cpuset named Charlie, to which are assigned the complete capacity of CPUs 2, 3 and 4, and their respective memory nodes.

Step Three: Start a process in a user CPUSET. The command:

- cset proc --set Charlie --exec -- stress -c 1 &

will start a process in the user CPUSET we just created. In this case, the new process is our workload generator.

Step Four: Move an existing process to a CPUSET. The command:

- cset proc --move --pid PID --toset=Charlie

will move an existing process (PID) into the CPUSET Charlie.

Step Five: List the tasks in a CPUSET, by using the command:

- cset proc --list --set Charlie

Step Six: Removing a CPUSET. Use the command:

- cset set --destroy Charlie

to remove the user CPUSET Charlie.

There, in six simple steps, is the complete lifecycle of a cpuset control group.

Linux Containers: The Future of Kernel Resource Management

Even as work continues on the subsystems for disk and network resource management, the next generation of kernel resource management technology is fast approaching production readiness. Linux containers (lxc) builds on all the control group infrastructure that we’ve talked about in this article—CPU, Memory, Namespace, Freezer, Checkpoint/Restart and Network—to provide fast, lightweight, OS-level virtualization without the need for the instruction interpretation or emulation normally provided by a hypervisor. It’s similar to Linux-VServer or OpenVZ.

Linux containers can be used to run an application, a service or a full (Linux) operating system, partially separated from the rest of the system, but with essentially native performance. In particular, disk I/O is undiminished and cpu and I/O scheduling are much more fair and tunable than with full virtualization. This makes it possible to contain disk I/O intensive applications such as databases, to manage their impact on other applications and processes.

Linux containers is provided as a technology preview in SUSE Linux Enterprise Server 11 Service Pack 1, and it is our intent to provide full production support in Service Pack 2. The lxc technology preview comes with rich online documentation (man lxc), including some implementation examples. Information on building and using Linux containers can be found on SourceForge, and on opensuse.org.

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