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Add per-cgroup cpuacct controller statistics like the system and user time consumed by the group of tasks. Changelog: v7 - Changed the name of the statistic from utime to user and from stime to system so that in future we could easily add other statistics like irq, softirq, steal times etc easily. v6 - Fixed a bug in the error path of cpuacct_create() (pointed by Li Zefan). v5 - In cpuacct_stats_show(), use cputime64_to_clock_t() since we are operating on a 64bit variable here. v4 - Remove comments in cpuacct_update_stats() which explained why rcu_read_lock() was needed (as per Peter Zijlstra's review comments). - Don't say that percpu_counter_read() is broken in Documentation/cpuacct.txt as per KAMEZAWA Hiroyuki's review comments. v3 - Fix a small race in the cpuacct hierarchy walk. v2 - stime and utime now exported in clock_t units instead of msecs. - Addressed the code review comments from Balbir and Li Zefan. - Moved to -tip tree. v1 - Moved the stime/utime accounting to cpuacct controller. Earlier versions - http://lkml.org/lkml/2009/2/25/129 Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com> Signed-off-by: Balaji Rao <balajirrao@gmail.com> Cc: Dhaval Giani <dhaval@linux.vnet.ibm.com> Cc: Paul Menage <menage@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Reviewed-by: Li Zefan <lizf@cn.fujitsu.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com> Tested-by: Balbir Singh <balbir@linux.vnet.ibm.com> LKML-Reference: <20090331043222.GA4093@in.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
51 lines
1.9 KiB
Plaintext
51 lines
1.9 KiB
Plaintext
CPU Accounting Controller
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The CPU accounting controller is used to group tasks using cgroups and
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account the CPU usage of these groups of tasks.
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The CPU accounting controller supports multi-hierarchy groups. An accounting
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group accumulates the CPU usage of all of its child groups and the tasks
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directly present in its group.
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Accounting groups can be created by first mounting the cgroup filesystem.
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# mkdir /cgroups
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# mount -t cgroup -ocpuacct none /cgroups
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With the above step, the initial or the parent accounting group
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becomes visible at /cgroups. At bootup, this group includes all the
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tasks in the system. /cgroups/tasks lists the tasks in this cgroup.
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/cgroups/cpuacct.usage gives the CPU time (in nanoseconds) obtained by
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this group which is essentially the CPU time obtained by all the tasks
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in the system.
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New accounting groups can be created under the parent group /cgroups.
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# cd /cgroups
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# mkdir g1
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# echo $$ > g1
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The above steps create a new group g1 and move the current shell
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process (bash) into it. CPU time consumed by this bash and its children
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can be obtained from g1/cpuacct.usage and the same is accumulated in
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/cgroups/cpuacct.usage also.
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cpuacct.stat file lists a few statistics which further divide the
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CPU time obtained by the cgroup into user and system times. Currently
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the following statistics are supported:
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user: Time spent by tasks of the cgroup in user mode.
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system: Time spent by tasks of the cgroup in kernel mode.
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user and system are in USER_HZ unit.
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cpuacct controller uses percpu_counter interface to collect user and
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system times. This has two side effects:
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- It is theoretically possible to see wrong values for user and system times.
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This is because percpu_counter_read() on 32bit systems isn't safe
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against concurrent writes.
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- It is possible to see slightly outdated values for user and system times
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due to the batch processing nature of percpu_counter.
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