On Saturday 03 May 2008 05:11:33 am Andrew Morton wrote:

<snip>
> > > >
> > > > percpu_counter_init uses kmalloc to create percpu counters. This
> > > > raises an early exception as kmem_cache is not initialized that
> > > > early.
> > >
> > > whaa?  kmalloc is ready to be used quite early in boot.  It's a bit of
> > > a concern that the CPU resource controller is doing stuff before even
> > > kmalloc is ready to go.
> >
> > No it doesn't. I placed the call to percpu_counter_init in sched_init.
> > Hence the problem.
>
> I'm groping in the dark without seeing the diff.
oh! am sorry about that! some cosmetic changes remain. It also contains some 
modifications done to the percpu_counter core.

<snip>
> > For the group_init_late() which you suggested, we should probably hook
> > into a place where kmalloc is ready and
> > account_user_time/account_system_time is not yet called even once. Does
> > it make sense ?
>
> yes, that would be good.
OK, so when does account_system_time get called for the first time ? after 
IRQs are set up, is it ? So, where do we place the hook ?

Here's the patch.

diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 9007ccd..8a1b756 100644
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -21,7 +21,7 @@ struct percpu_counter {
 #ifdef CONFIG_HOTPLUG_CPU
 	struct list_head list;	/* All percpu_counters are on a list */
 #endif
-	s32 *counters;
+	s32 counters[NR_CPUS];
 };
 
 #if NR_CPUS >= 16
diff --git a/kernel/sched.c b/kernel/sched.c
index bbdc32a..fde11f8 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -68,6 +68,7 @@
 #include <linux/hrtimer.h>
 #include <linux/tick.h>
 #include <linux/ftrace.h>
+#include <linux/percpu_counter.h>
 
 #include <asm/tlb.h>
 #include <asm/irq_regs.h>
@@ -248,10 +249,34 @@ 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];
+};
+
+/* Called under irq disable. */
+static void __cpu_cgroup_stat_add(struct cpu_cgroup_stat *stat,
+		enum cpu_cgroup_stat_index idx, int val)
+{
+		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 +3862,16 @@ 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
 }
 
 /*
@@ -3900,6 +3935,15 @@ void account_system_time(struct task_struct *p, int hardirq_offset,
 		cpustat->idle = cputime64_add(cpustat->idle, tmp);
 	/* Account for system time used */
 	acct_update_integrals(p);
+
+#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
 }
 
 /*
@@ -7426,6 +7470,10 @@ void __init sched_init(void)
 #ifdef CONFIG_GROUP_SCHED
 	list_add(&init_task_group.list, &task_groups);
 #endif
+	
+	for(i = 0; i < CPU_CGROUP_STAT_NSTATS; i++) {
+		percpu_counter_init(&init_task_group.stat.cpustat[i], 0);
+	}
 
 	for_each_possible_cpu(i) {
 		struct rq *rq;
@@ -8183,10 +8231,12 @@ 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 */
 		init_task_group.css.cgroup = cgrp;
+		/* Initialize init_task_grp's stat object */
 		return &init_task_group.css;
 	}
 
@@ -8201,6 +8251,10 @@ cpu_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cgrp)
 	/* Bind the cgroup to task_group object we just created */
 	tg->css.cgroup = cgrp;
 
+	/* Initialize the stats object */
+	for(i = 0; i < CPU_CGROUP_STAT_NSTATS; i++)
+		percpu_counter_init(&tg->stat.cpustat[i], 0);
+
 	return &tg->css;
 }
 
@@ -8249,6 +8303,36 @@ static u64 cpu_shares_read_u64(struct cgroup *cgrp, struct cftype *cft)
 
 	return (u64) tg->shares;
 }
+
+static s64 cpu_cgroup_read_stat(struct cpu_cgroup_stat *stat,
+		enum cpu_cgroup_stat_index idx)
+{
+	return percpu_counter_read(&stat->cpustat[idx]);
+}
+
+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;
+}
 #endif
 
 #ifdef CONFIG_RT_GROUP_SCHED
@@ -8295,6 +8379,10 @@ 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)
@@ -8310,7 +8398,7 @@ struct cgroup_subsys cpu_cgroup_subsys = {
 	.attach		= cpu_cgroup_attach,
 	.populate	= cpu_cgroup_populate,
 	.subsys_id	= cpu_cgroup_subsys_id,
-	.early_init	= 1,
+//	.early_init	= 1,
 };
 
 #endif	/* CONFIG_CGROUP_SCHED */
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index 1191744..a7e84f9 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -14,6 +14,7 @@ static LIST_HEAD(percpu_counters);
 static DEFINE_MUTEX(percpu_counters_lock);
 #endif
 
+#define per_cpu_ptr(var,cpu) &var[cpu]
 void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
 {
 	int cpu;
@@ -74,7 +75,6 @@ int percpu_counter_init(struct percpu_counter *fbc, s64 amount)
 {
 	spin_lock_init(&fbc->lock);
 	fbc->count = amount;
-	fbc->counters = alloc_percpu(s32);
 	if (!fbc->counters)
 		return -ENOMEM;
 #ifdef CONFIG_HOTPLUG_CPU
@@ -102,7 +102,6 @@ void percpu_counter_destroy(struct percpu_counter *fbc)
 		return;
 
 	free_percpu(fbc->counters);
-	fbc->counters = NULL;
 #ifdef CONFIG_HOTPLUG_CPU
 	mutex_lock(&percpu_counters_lock);
 	list_del(&fbc->list);

-- 
Warm Regards,

Balaji Rao
Dept. of Mechanical Engineering
NITK
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