sched/fair: Remove task and group entity load when they are dead

When task exits or group is destroyed, the entity's load should be
removed from its parent cfs_rq's load. Otherwise, it will take time
for the parent cfs_rq to decay the dead entity's load to 0, which
is not desired.

Signed-off-by: Yuyang Du <yuyang.du@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: arjan@linux.intel.com
Cc: bsegall@google.com
Cc: dietmar.eggemann@arm.com
Cc: fengguang.wu@intel.com
Cc: len.brown@intel.com
Cc: morten.rasmussen@arm.com
Cc: pjt@google.com
Cc: rafael.j.wysocki@intel.com
Cc: umgwanakikbuti@gmail.com
Cc: vincent.guittot@linaro.org
Link: http://lkml.kernel.org/r/1436918682-4971-6-git-send-email-yuyang.du@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

@@ -4913,6 +4913,11 @@ static void migrate_task_rq_fair(struct task_struct *p, int next_cpu)
 	/* We have migrated, no longer consider this task hot */
 	p->se.exec_start = 0;
 }
+
+static void task_dead_fair(struct task_struct *p)
+{
+	remove_entity_load_avg(&p->se);
+}
 #endif /* CONFIG_SMP */
 
 static unsigned long
@@ -7991,9 +7996,12 @@ void free_fair_sched_group(struct task_group *tg)
 	for_each_possible_cpu(i) {
 		if (tg->cfs_rq)
 			kfree(tg->cfs_rq[i]);
-		if (tg->se)
+		if (tg->se) {
+			if (tg->se[i])
+				remove_entity_load_avg(tg->se[i]);
 			kfree(tg->se[i]);
 		}
+	}
 
 	kfree(tg->cfs_rq);
 	kfree(tg->se);
@@ -8179,6 +8187,7 @@ const struct sched_class fair_sched_class = {
 	.rq_offline		= rq_offline_fair,
 
 	.task_waking		= task_waking_fair,
+	.task_dead		= task_dead_fair,
 #endif
 
 	.set_curr_task          = set_curr_task_fair,