2 files changed, 41 insertions, 3 deletions

diff --git a/Documentation/controllers/cpuacct.txt b/Documentation/controllers/cpuacct.txt
new file mode 100644
index 000000000000..bb775fbe43d7
--- /dev/null
+++ b/Documentation/controllers/cpuacct.txt
@@ -0,0 +1,32 @@
+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.
diff --git a/kernel/sched.c b/kernel/sched.c
index 59db86c915f9..ebaf432365f6 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -9196,11 +9196,12 @@ struct cgroup_subsys cpu_cgroup_subsys = {
  * (balbir@in.ibm.com).
  */
 
-/* track cpu usage of a group of tasks */
+/* track cpu usage of a group of tasks and its child groups */
 struct cpuacct {
         struct cgroup_subsys_state css;
         /* cpuusage holds pointer to a u64-type object on every cpu */
         u64 *cpuusage;
+        struct cpuacct *parent;
 };
 
 struct cgroup_subsys cpuacct_subsys;
@@ -9234,6 +9235,9 @@ static struct cgroup_subsys_state *cpuacct_create(
                 return ERR_PTR(-ENOMEM);
         }
 
+        if (cgrp->parent)
+                ca->parent = cgroup_ca(cgrp->parent);
+
         return &ca->css;
 }
 
@@ -9313,14 +9317,16 @@ static int cpuacct_populate(struct cgroup_subsys *ss, struct cgroup *cgrp)
 static void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 {
         struct cpuacct *ca;
+        int cpu;
 
         if (!cpuacct_subsys.active)
                 return;
 
+        cpu = task_cpu(tsk);
         ca = task_ca(tsk);
-        if (ca) {
-                u64 *cpuusage = percpu_ptr(ca->cpuusage, task_cpu(tsk));
 
+        for (; ca; ca = ca->parent) {
+                u64 *cpuusage = percpu_ptr(ca->cpuusage, cpu);
                 *cpuusage += cputime;
         }
 }