[RFD 7/9] provide a version of cpuacct statistics inside cpu cgroup

[Glauber Costa <glommer@parallels.com>]

For users interested in using the information currently displayed
at cpuacct.stat, we provide it inside the cpu cgroup.

This have the advantage of accounting this information only once,
instead of twice, when there is no need to have an independent group
of tasks for controlling and accounting, leading to a lot less overhead.

Signed-off-by: Glauber Costa <glommer@parallels.com>
CC: Balbir Singh <bsingharora@gmail.com>
---
 kernel/sched.c |   42 +++++++++++++++++++++++++++++++++++++-----
 1 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 8a510ab..b687441 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -9296,6 +9296,39 @@ int cpu_cgroup_proc_stat(struct cgroup *cgrp, struct cftype *cft, struct seq_fil
 
 
 
+static const char *cpuacct_stat_desc[] = {
+	[CPUACCT_STAT_USER] = "user",
+	[CPUACCT_STAT_SYSTEM] = "system",
+};
+
+static int cpu_cgroup_stats_show(struct cgroup *cgrp, struct cftype *cft,
+		struct cgroup_map_cb *cb)
+{
+	struct task_group *tg = cgroup_tg(cgrp);
+	int cpu;
+	s64 val = 0;
+
+	for_each_online_cpu(cpu) {
+		struct kernel_stat *kstat = per_cpu_ptr(tg->cpustat, cpu);
+		val += kstat->cpustat[USER];
+		val += kstat->cpustat[NICE];
+	}
+	val = cputime64_to_clock_t(val);
+	cb->fill(cb, cpuacct_stat_desc[CPUACCT_STAT_USER], val);
+
+	val = 0;
+	for_each_online_cpu(cpu) {
+		struct kernel_stat *kstat = per_cpu_ptr(tg->cpustat, cpu);
+		val += kstat->cpustat[SYSTEM];
+		val += kstat->cpustat[IRQ];
+		val += kstat->cpustat[SOFTIRQ];
+	}
+
+	val = cputime64_to_clock_t(val);
+	cb->fill(cb, cpuacct_stat_desc[CPUACCT_STAT_SYSTEM], val);
+
+	return 0;
+}
 static struct cftype cpu_files[] = {
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	{
@@ -9320,6 +9353,10 @@ static struct cftype cpu_files[] = {
 		.name = "proc.stat",
 		.read_seq_string = cpu_cgroup_proc_stat,
 	},
+	{
+		.name = "stat",
+		.read_map = cpu_cgroup_stats_show,
+	},
 };
 
 static int cpu_cgroup_populate(struct cgroup_subsys *ss, struct cgroup *cont)
@@ -9503,11 +9540,6 @@ static int cpuacct_percpu_seq_read(struct cgroup *cgroup, struct cftype *cft,
 	return 0;
 }
 
-static const char *cpuacct_stat_desc[] = {
-	[CPUACCT_STAT_USER] = "user",
-	[CPUACCT_STAT_SYSTEM] = "system",
-};
-
 static int cpuacct_stats_show(struct cgroup *cgrp, struct cftype *cft,
 		struct cgroup_map_cb *cb)
 {
-- 
1.7.6