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-CPU Accounting Controller
-The CPU accounting controller is used to group tasks using cgroups and
-account the CPU usage of these groups of tasks.
-The CPU accounting controller supports multi-hierarchy groups. An accounting
-group accumulates the CPU usage of all of its child groups and the tasks
-directly present in its group.
-Accounting groups can be created by first mounting the cgroup filesystem.
-# mount -t cgroup -ocpuacct none /sys/fs/cgroup
-With the above step, the initial or the parent accounting group becomes
-visible at /sys/fs/cgroup. At bootup, this group includes all the tasks in
-the system. /sys/fs/cgroup/tasks lists the tasks in this cgroup.
-/sys/fs/cgroup/cpuacct.usage gives the CPU time (in nanoseconds) obtained
-by this group which is essentially the CPU time obtained by all the tasks
-in the system.
-New accounting groups can be created under the parent group /sys/fs/cgroup.
-# cd /sys/fs/cgroup
-# mkdir g1
-# echo $$ > g1/tasks
-The above steps create a new group g1 and move the current shell
-process (bash) into it. CPU time consumed by this bash and its children
-can be obtained from g1/cpuacct.usage and the same is accumulated in
-/sys/fs/cgroup/cpuacct.usage also.
-cpuacct.stat file lists a few statistics which further divide the
-CPU time obtained by the cgroup into user and system times. Currently
-the following statistics are supported:
-user: Time spent by tasks of the cgroup in user mode.
-system: Time spent by tasks of the cgroup in kernel mode.
-user and system are in USER_HZ unit.
-cpuacct controller uses percpu_counter interface to collect user and
-system times. This has two side effects:
-- It is theoretically possible to see wrong values for user and system times.
- This is because percpu_counter_read() on 32bit systems isn't safe
- against concurrent writes.
-- It is possible to see slightly outdated values for user and system times
- due to the batch processing nature of percpu_counter.