6255c46fa0
cgroup-legacy may be too loaded. Rename the docs so that they're postfixed with v1 and v2. * s/cgroup-legacy/cgroup-v1/ * s/cgroup.txt/cgroup-v2.txt/ Signed-off-by: Tejun Heo <tj@kernel.org>
49 lines
1.9 KiB
Text
49 lines
1.9 KiB
Text
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- It is possible to see slightly outdated values for user and system times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.
|