sched: Extend active balance to accept 'push_task' argument

Active balance currently picks one task to migrate from busy cpu to
a chosen cpu (push_cpu). This patch extends active load balance to
recognize a particular task ('push_task') that needs to be migrated to
'push_cpu'. This capability will be leveraged by HMP-aware task
placement in a subsequent patch.

Change-Id: If31320111e6cc7044e617b5c3fd6d8e0c0e16952
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>
[rameezmustafa@codeaurora.org]: Port to msm-3.18]
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>

Author: Srivatsa Vaddagiri

kernel/sched/core.c

@@ -7909,6 +7909,7 @@ void __init sched_init(void)
 		rq->active_balance = 0;
 		rq->next_balance = jiffies;
 		rq->push_cpu = 0;
+		rq->push_task = NULL;
 		rq->cpu = i;
 		rq->online = 0;
 		rq->idle_stamp = 0;

kernel/sched/fair.c

@@ -9429,8 +9429,18 @@ static int active_load_balance_cpu_stop(void *data)
 	int busiest_cpu = cpu_of(busiest_rq);
 	int target_cpu = busiest_rq->push_cpu;
 	struct rq *target_rq = cpu_rq(target_cpu);
-	struct sched_domain *sd;
+	struct sched_domain *sd = NULL;
 	struct task_struct *p = NULL;
+	struct task_struct *push_task;
+	int push_task_detached = 0;
+	struct lb_env env = {
+		.sd		= sd,
+		.dst_cpu	= target_cpu,
+		.dst_rq		= target_rq,
+		.src_cpu	= busiest_rq->cpu,
+		.src_rq		= busiest_rq,
+		.idle		= CPU_IDLE,
+	};
 
 	raw_spin_lock_irq(&busiest_rq->lock);
 
@@ -9450,6 +9460,16 @@ static int active_load_balance_cpu_stop(void *data)
 	 */
 	BUG_ON(busiest_rq == target_rq);
 
+	push_task = busiest_rq->push_task;
+	if (push_task) {
+		if (task_on_rq_queued(push_task) &&
+				task_cpu(push_task) == busiest_cpu) {
+			detach_task(push_task, &env);
+			push_task_detached = 1;
+		}
+		goto out_unlock;
+	}
+
 	/* Search for an sd spanning us and the target CPU. */
 	rcu_read_lock();
 	for_each_domain(target_cpu, sd) {
@@ -9459,15 +9479,7 @@ static int active_load_balance_cpu_stop(void *data)
 	}
 
 	if (likely(sd)) {
-		struct lb_env env = {
-			.sd		= sd,
-			.dst_cpu	= target_cpu,
-			.dst_rq		= target_rq,
-			.src_cpu	= busiest_rq->cpu,
-			.src_rq		= busiest_rq,
-			.idle		= CPU_IDLE,
-		};
-
+		env.sd = sd;
 		schedstat_inc(sd, alb_count);
 		update_rq_clock(busiest_rq);
 
@@ -9485,8 +9497,18 @@ static int active_load_balance_cpu_stop(void *data)
 	rcu_read_unlock();
 out_unlock:
 	busiest_rq->active_balance = 0;
+
+	if (push_task)
+		busiest_rq->push_task = NULL;
+
 	raw_spin_unlock(&busiest_rq->lock);
 
+	if (push_task) {
+		if (push_task_detached)
+			attach_one_task(target_rq, push_task);
+		put_task_struct(push_task);
+	}
+
 	if (p)
 		attach_one_task(target_rq, p);
 

kernel/sched/sched.h

@@ -664,6 +664,7 @@ struct rq {
 	/* For active balancing */
 	int active_balance;
 	int push_cpu;
+	struct task_struct *push_task;
 	struct cpu_stop_work active_balance_work;
 	/* cpu of this runqueue: */
 	int cpu;