[RFC][-mm] Simple stats for cpu resource controller v3

[Balaji Rao]

This implements a couple of basic statistics for the CPU resource controller. 

v2->v3
-------
Proper locking while collecting stats. Thanks to Peter Zijlstra for suggesting
the delta approach.

This applies against 2.6.25-mm1
---

Signed-off-by: Balaji Rao <balajirrao@xxxxxxxxx>

diff --git a/kernel/sched.c b/kernel/sched.c
index bbdc32a..5bda75a 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -248,10 +248,51 @@ 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_cpu {
+	s64 count[CPU_CGROUP_STAT_NSTATS];
+	u32 delta[CPU_CGROUP_STAT_NSTATS];
+} ____cacheline_aligned_in_smp;
+
+struct cpu_cgroup_stat {
+	struct cpu_cgroup_stat_cpu cpustat[NR_CPUS];
+	spinlock_t lock;
+};
+
+/* Called under irq disable. */
+static void __cpu_cgroup_stat_add(struct cpu_cgroup_stat *stat,
+		enum cpu_cgroup_stat_index idx, int val)
+{
+	int cpu = smp_processor_id();
+	unsigned long flags;
+
+	BUG_ON(!irqs_disabled());
+	stat->cpustat[cpu].delta[idx] += val;
+
+	if (stat->cpustat[cpu].delta[idx] > CPU_CGROUP_STAT_THRESHOLD) {
+		spin_lock_irqsave(&stat->lock, flags);
+		stat->cpustat[cpu].count[idx] += stat->cpustat[cpu].delta[idx];
+		stat->cpustat[cpu].delta[idx] = 0;
+		spin_unlock_irqrestore(&stat->lock, flags);
+	}
+}
+#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 +3878,16 @@ 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 +3951,15 @@ 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
 }
 
 /*
@@ -7838,7 +7898,9 @@ struct task_group *sched_create_group(void)
 	}
 	list_add_rcu(&tg->list, &task_groups);
 	spin_unlock_irqrestore(&task_group_lock, flags);
-
+#ifdef CONFIG_CGROUP_SCHED
+	spin_lock_init(&tg->stat.lock);
+#endif
 	return tg;
 
 err:
@@ -8249,6 +8311,48 @@ 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)
+{
+	int cpu;
+	s64 ret = 0;
+	unsigned long flags;
+
+	spin_lock_irqsave(&stat->lock, flags);
+	for_each_possible_cpu(cpu) {
+		stat->cpustat[cpu].count[idx] += stat->cpustat[cpu].delta[idx];
+		stat->cpustat[cpu].delta[idx] = 0;
+		ret += stat->cpustat[cpu].count[idx];
+	}
+	spin_unlock_irqrestore(&stat->lock, flags);
+
+	return ret;
+}
+
+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 < ARRAY_SIZE(stat->cpustat[0].count); 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 +8399,10 @@ 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)

-- 
Warm Regards,

Balaji Rao
Dept. of Mechanical Engineering
NITK
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