Configuring cgroups to Control CPU Usage

yum install libcgroup

Soft Limit Parameter

You set the soft limit with the cpu.shares parameter. This parameter takes an integer value, which specifies a relative share of CPU time available to the tasks in a cgroup. For example, if there are two tasks and cpu.shares is set to 100, each task receives half of the CPU time. The value must be 2 or greater. When you set a soft limit, Drill can exceed the CPU allocated if extra CPU is available for use on the system. Drill can continue to use CPU until there is contention with other processes over the CPU or Drill hits the hard limit.

Hard Limit Parameters

You set the hard limit on the amount of CPU time that the Drill process can use through the cpu.cfs_period_us and cpu.cfs_quota_us parameters.

• cpu.cfs_period_us

  Specifies a period in microseconds (represented by us for µs) to indicate how often a cgroup's access to CPU resources should be reallocated. For example, if you want tasks in a cgroup to have access to a single CPU for 0.2 seconds in a 1 second window, set cpu.cfs_quota_us to 200000 and cpu.cfs_period_us to 1000000. The upper limit of the cpu.cfs_quota_us parameter is 1 second and the lower limit is 1000 microseconds.

• cpu.cfs_quota_us

  Specifies the total amount of runtime in microseconds (represented by us for µs), for which all tasks in the Drill cgroup can run during one period (as defined by cpu.cfs_period_us). When tasks in the Drill cgroup use up all the time specified by the quota, the tasks are throttled for the remainder of the time specified by the period and they cannot run until the next period. For example, if tasks in the Drill cgroup can access a single CPU for 0.2 seconds out of every 1 second, set cpu.cfs_quota_us to 200000 and cpu.cfs_period_us to 1000000. Setting the cpu.cfs_quota_us value to -1 indicates that the group does not have any restrictions on CPU. This is the default value for every cgroup, except for the root cgroup.

1. Start the cgconfig service:

   service cgconfig start

2. Add a cgroup for Drill in the /etc/cgconfig.conf file:

   group drillcpu {
                        cpu {
                               cpu.shares = 320;
                               cpu.cfs_quota_us = 400000;
                               cpu.cfs_period_us = 100000;
                               }
                        }  

   In the configuration example above, the cpu.shares parameter sets the soft limit. The other two parameters, cpu.cfs_quota_us and cpu.cfs_period_us, set the hard limit. If you prefer to set only one type of limit, remove the parameters that do not apply. When setting a soft limit, allocate a specific number of CPU shares to the Drill cgroup in the configuration. Calculate the CPU shares as:

   1024 (CPU allocated to Drill/Total available CPU)

   In the example, CPU shares is calculated as:

   1024 (10/32) = 320

   When setting a hard limit, add limits to the cpu.cfs_quota_us and cpu.cfs_period_us parameters. In the example, the Drill process can fully utilize 4 CPU.

   TIP

   The hard limit parameter settings persist after each cgroup service restart. Alternatively, you can set the parameters at the session level using the following commands:

   echo 400000 > /cgroup/cpu/drillcpu/cpu.cfs_quota_us
          echo 100000 > /cgroup/cpu/drillcpu/cpu.cfs_period_us

3. (Optional) If you want the cgconfig service to automatically restart upon system reboots, run the following command:

   chkconfig cgconfig on