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authorLinus Torvalds <torvalds@linux-foundation.org>2009-04-09 10:37:28 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-04-09 10:37:28 -0700
commit17b2e9bf27d417bc186cc922b4d6d5eaa048f9d8 (patch)
tree7ae99be289ec2ffe68aa38926d9e9a13e4387ee0 /Documentation
parent422a253483aa5de71a2bcdc27b0aa023053f97f8 (diff)
parente3c8ca8336707062f3f7cb1cd7e6b3c753baccdd (diff)
Merge branch 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: sched: do not count frozen tasks toward load sched: refresh MAINTAINERS entry sched: Print sched_group::__cpu_power in sched_domain_debug cpuacct: add per-cgroup utime/stime statistics posixtimers, sched: Fix posix clock monotonicity sched_rt: don't allocate cpumask in fastpath cpuacct: make cpuacct hierarchy walk in cpuacct_charge() safe when rcupreempt is used -v2
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/cgroups/cpuacct.txt18
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/cgroups/cpuacct.txt b/Documentation/cgroups/cpuacct.txt
index bb775fbe43d..8b930946c52 100644
--- a/Documentation/cgroups/cpuacct.txt
+++ b/Documentation/cgroups/cpuacct.txt
@@ -30,3 +30,21 @@ 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+- It is possible to see slightly outdated values for user and system times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.