[RFC v1 PATCH 2/7] sched: Maintain aggregated tasks count in cfs_rq at each hierarchy level

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

sched: Maintain aggregated tasks count in cfs_rq at each hierarchy level

From: Bharata B Rao <bharata@linux.vnet.ibm.com>

This patch adds a counter to cfs_rq (->nr_tasks_running) to record the
aggregated tasks count at each level in the task group hierarchy.
This is needed by later hard limit patches where it is required to
know how many tasks go off the rq when a throttled group entity
is dequeued.

Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
---
 kernel/sched.c       |    4 ++++
 kernel/sched_debug.c |    2 ++
 kernel/sched_fair.c  |   23 +++++++++++++++++++++++
 3 files changed, 29 insertions(+)

--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -477,6 +477,10 @@ struct cfs_rq {
 	unsigned long rq_weight;
 #endif
 #endif
+	/*
+	 * Number of tasks at this heirarchy.
+	 */
+	unsigned long nr_tasks_running;
 };
 
 /* Real-Time classes' related field in a runqueue: */
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -214,6 +214,8 @@ void print_cfs_rq(struct seq_file *m, in
 #ifdef CONFIG_SMP
 	SEQ_printf(m, "  .%-30s: %lu\n", "shares", cfs_rq->shares);
 #endif
+	SEQ_printf(m, "  .%-30s: %ld\n", "nr_tasks_running",
+			cfs_rq->nr_tasks_running);
 	print_cfs_group_stats(m, cpu, cfs_rq->tg);
 #endif
 }
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -243,6 +243,27 @@ find_matching_se(struct sched_entity **s
 
 #endif	/* CONFIG_FAIR_GROUP_SCHED */
 
+static void add_cfs_rq_tasks_running(struct sched_entity *se,
+		unsigned long count)
+{
+	struct cfs_rq *cfs_rq;
+
+	for_each_sched_entity(se) {
+		cfs_rq = cfs_rq_of(se);
+		cfs_rq->nr_tasks_running += count;
+	}
+}
+
+static void sub_cfs_rq_tasks_running(struct sched_entity *se,
+		unsigned long count)
+{
+	struct cfs_rq *cfs_rq;
+
+	for_each_sched_entity(se) {
+		cfs_rq = cfs_rq_of(se);
+		cfs_rq->nr_tasks_running -= count;
+	}
+}
 
 /**************************************************************
  * Scheduling class tree data structure manipulation methods:
@@ -969,6 +990,7 @@ static void enqueue_task_fair(struct rq 
 		wakeup = 1;
 	}
 
+	add_cfs_rq_tasks_running(&p->se, 1);
 	hrtick_update(rq);
 }
 
@@ -991,6 +1013,7 @@ static void dequeue_task_fair(struct rq 
 		sleep = 1;
 	}
 
+	sub_cfs_rq_tasks_running(&p->se, 1);
 	hrtick_update(rq);
 }