mirror of https://gitee.com/openkylin/linux.git
51 lines
1.9 KiB
Plaintext
51 lines
1.9 KiB
Plaintext
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.
|
|
|
|
# mkdir /cgroups
|
|
# mount -t cgroup -ocpuacct none /cgroups
|
|
|
|
With the above step, the initial or the parent accounting group
|
|
becomes visible at /cgroups. At bootup, this group includes all the
|
|
tasks in the system. /cgroups/tasks lists the tasks in this cgroup.
|
|
/cgroups/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 /cgroups.
|
|
|
|
# cd /cgroups
|
|
# mkdir g1
|
|
# echo $$ > g1
|
|
|
|
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
|
|
/cgroups/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- It is possible to see slightly outdated values for user and system times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.
|