sched: add hierarchical accounting to cpu accounting controller

Impact: improve CPU time accounting of tasks under the cpu accounting controller

Add hierarchical accounting to cpu accounting controller and include
cpuacct documentation.

Currently, while charging the task's cputime to its accounting group,
the accounting group hierarchy isn't updated. This patch charges the cputime
of a task to its accounting group and all its parent accounting groups.

Reported-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Reviewed-by: Paul Menage <menage@google.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 9 insertions, 3 deletions

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;
 	}
 }