Hi Andrew,

Here's a version that uses percpu_counters and which actually works. The 
only evil it contains is the check, 

	if (percpu_counter_ready) {
		..
	}

I've also added a callback called 'initalize' to a cgroup_subsys.

The alternate idea I suggested was to add a hook at a point where the first 
task has not yet started and where kmalloc is usable. Its hacky and not a 
nice thing to do IMHO.

How does this look ?

Regards,
Balaji Rao

---

Signed-off-by: Balaji Rao <balajirrao@gmail.com>

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index e155aa7..60a25cb 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -293,6 +293,7 @@ int cgroup_is_descendant(const struct cgroup *cgrp);
 struct cgroup_subsys {
 	struct cgroup_subsys_state *(*create)(struct cgroup_subsys *ss,
 						  struct cgroup *cgrp);
+	void (*initialize)(int early);
 	void (*pre_destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp);
 	void (*destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp);
 	int (*can_attach)(struct cgroup_subsys *ss,
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 8877a08..be37395 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2553,6 +2553,9 @@ int __init cgroup_init_early(void)
 
 		if (ss->early_init)
 			cgroup_init_subsys(ss);
+
+		if (ss->initialize)
+			ss->initialize(1);
 	}
 	return 0;
 }
@@ -2577,6 +2580,9 @@ int __init cgroup_init(void)
 		struct cgroup_subsys *ss = subsys[i];
 		if (!ss->early_init)
 			cgroup_init_subsys(ss);
+
+		if (ss->initialize)
+			ss->initialize(0);
 	}
 
 	/* Add init_css_set to the hash table */
diff --git a/kernel/sched.c b/kernel/sched.c
index bbdc32a..50f737e 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -247,11 +247,32 @@ static void destroy_rt_bandwidth(struct rt_bandwidth *rt_b)
 struct cfs_rq;
 
 static LIST_HEAD(task_groups);
+#ifdef CONFIG_CGROUP_SCHED
+#define CPU_CGROUP_STAT_THRESHOLD (1 << 30)
+enum cpu_cgroup_stat_index {
+	CPU_CGROUP_STAT_UTIME, /* Usertime of the task group */
+	CPU_CGROUP_STAT_STIME, /* Kerneltime of the task group */
+
+	CPU_CGROUP_STAT_NSTATS,
+};
+
+struct cpu_cgroup_stat {
+	struct percpu_counter cpustat[CPU_CGROUP_STAT_NSTATS];
+};
+
+static void __cpu_cgroup_stat_add(struct cpu_cgroup_stat *stat,
+		enum cpu_cgroup_stat_index idx, int val)
+{
+	if (stat)
+		percpu_counter_add(&stat->cpustat[idx], val);
+}
+#endif
 
 /* task group related information */
 struct task_group {
 #ifdef CONFIG_CGROUP_SCHED
 	struct cgroup_subsys_state css;
+	struct cpu_cgroup_stat *stat;
 #endif
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
@@ -3837,6 +3858,16 @@ void account_user_time(struct task_struct *p, cputime_t cputime)
 		cpustat->nice = cputime64_add(cpustat->nice, tmp);
 	else
 		cpustat->user = cputime64_add(cpustat->user, tmp);
+
+       /* Charge the task's group */
+#ifdef CONFIG_CGROUP_SCHED
+	{
+		struct task_group *tg;
+		tg = task_group(p);
+		__cpu_cgroup_stat_add(tg->stat, CPU_CGROUP_STAT_UTIME,
+				cputime_to_msecs(cputime));
+	}
+#endif
 }
 
 /*
@@ -3892,8 +3923,17 @@ void account_system_time(struct task_struct *p, int hardirq_offset,
 		cpustat->irq = cputime64_add(cpustat->irq, tmp);
 	else if (softirq_count())
 		cpustat->softirq = cputime64_add(cpustat->softirq, tmp);
-	else if (p != rq->idle)
+	else if (p != rq->idle) {
 		cpustat->system = cputime64_add(cpustat->system, tmp);
+#ifdef CONFIG_CGROUP_SCHED
+		{
+			struct task_group *tg;
+			tg = task_group(p);
+			__cpu_cgroup_stat_add(tg->stat, CPU_CGROUP_STAT_STIME,
+					cputime_to_msecs(cputime));
+		}
+	}
+#endif
 	else if (atomic_read(&rq->nr_iowait) > 0)
 		cpustat->iowait = cputime64_add(cpustat->iowait, tmp);
 	else
@@ -8179,10 +8219,26 @@ static inline struct task_group *cgroup_tg(struct cgroup *cgrp)
 			    struct task_group, css);
 }
 
+static void cpu_cgroup_initialize(int early)
+{
+	int i;
+	struct cpu_cgroup_stat *stat;
+
+	if (!early) {
+		stat = kmalloc(sizeof(struct cpu_cgroup_stat)
+				, GFP_KERNEL);
+		for (i = 0; i < CPU_CGROUP_STAT_NSTATS; i++)
+			percpu_counter_init(
+					&stat->cpustat[i], 0);
+		init_task_group.stat = stat;
+	}
+}
+
 static struct cgroup_subsys_state *
 cpu_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cgrp)
 {
 	struct task_group *tg;
+	int i;
 
 	if (!cgrp->parent) {
 		/* This is early initialization for the top cgroup */
@@ -8198,6 +8254,10 @@ cpu_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cgrp)
 	if (IS_ERR(tg))
 		return ERR_PTR(-ENOMEM);
 
+	tg->stat = kmalloc(sizeof(struct cpu_cgroup_stat), GFP_KERNEL);
+	for (i = 0; i < CPU_CGROUP_STAT_NSTATS; i++)
+		percpu_counter_init(&tg->stat->cpustat[i], 0);
+
 	/* Bind the cgroup to task_group object we just created */
 	tg->css.cgroup = cgrp;
 
@@ -8251,6 +8311,38 @@ static u64 cpu_shares_read_u64(struct cgroup *cgrp, struct cftype *cft)
 }
 #endif
 
+static s64 cpu_cgroup_read_stat(struct cpu_cgroup_stat *stat,
+		enum cpu_cgroup_stat_index idx)
+{
+	if (stat)
+		return percpu_counter_read(&stat->cpustat[idx]);
+
+	return 0;
+}
+
+static const struct cpu_cgroup_stat_desc {
+	const char *msg;
+	u64 unit;
+} cpu_cgroup_stat_desc[] = {
+	[CPU_CGROUP_STAT_UTIME] = { "utime", 1, },
+	[CPU_CGROUP_STAT_STIME] = { "stime", 1, },
+};
+
+static int cpu_cgroup_stats_show(struct cgroup *cgrp, struct cftype *cft,
+		struct cgroup_map_cb *cb)
+{
+	struct task_group *tg = cgroup_tg(cgrp);
+	struct cpu_cgroup_stat *stat = tg->stat;
+	int i;
+	for (i = 0; i < CPU_CGROUP_STAT_NSTATS; i++) {
+		s64 val;
+		val = cpu_cgroup_read_stat(stat, i);
+		val *= cpu_cgroup_stat_desc[i].unit;
+		cb->fill(cb, cpu_cgroup_stat_desc[i].msg, val);
+	}
+	return 0;
+}
+
 #ifdef CONFIG_RT_GROUP_SCHED
 static ssize_t cpu_rt_runtime_write(struct cgroup *cgrp, struct cftype *cft,
 				s64 val)
@@ -8295,6 +8387,10 @@ static struct cftype cpu_files[] = {
 		.write_u64 = cpu_rt_period_write_uint,
 	},
 #endif
+	{
+		.name = "stat",
+		.read_map = cpu_cgroup_stats_show,
+	},
 };
 
 static int cpu_cgroup_populate(struct cgroup_subsys *ss, struct cgroup *cont)
@@ -8304,6 +8400,7 @@ static int cpu_cgroup_populate(struct cgroup_subsys *ss, struct cgroup *cont)
 
 struct cgroup_subsys cpu_cgroup_subsys = {
 	.name		= "cpu",
+	.initialize	= cpu_cgroup_initialize,
 	.create		= cpu_cgroup_create,
 	.destroy	= cpu_cgroup_destroy,
 	.can_attach	= cpu_cgroup_can_attach,
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