sched/fair: cpufreq_sched triggers for load balancing

As we don't trigger freq changes from {en,de}queue_task_fair() during load
balancing, we need to do explicitly so on load balancing paths.

[smuckle@linaro.org: move update_capacity_of calls so rq lock is held]

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Juri Lelli <juri.lelli@arm.com>
Signed-off-by: Steve Muckle <smuckle@linaro.org>

kernel/sched/fair.c

@@ -6405,6 +6405,10 @@ static void attach_one_task(struct rq *rq, struct task_struct *p)
 {
 	raw_spin_lock(&rq->lock);
 	attach_task(rq, p);
+	/*
+	 * We want to potentially raise target_cpu's OPP.
+	 */
+	update_capacity_of(cpu_of(rq));
 	raw_spin_unlock(&rq->lock);
 }
 
@@ -6426,6 +6430,11 @@ static void attach_tasks(struct lb_env *env)
 		attach_task(env->dst_rq, p);
 	}
 
+	/*
+	 * We want to potentially raise env.dst_cpu's OPP.
+	 */
+	update_capacity_of(env->dst_cpu);
+
 	raw_spin_unlock(&env->dst_rq->lock);
 }
 
@@ -7688,6 +7697,11 @@ more_balance:
 		 * ld_moved     - cumulative load moved across iterations
 		 */
 		cur_ld_moved = detach_tasks(&env);
+		/*
+		 * We want to potentially lower env.src_cpu's OPP.
+		 */
+		if (cur_ld_moved)
+			update_capacity_of(env.src_cpu);
 
 		/*
 		 * We've detached some tasks from busiest_rq. Every
@@ -8058,8 +8072,13 @@ static int active_load_balance_cpu_stop(void *data)
 		schedstat_inc(sd, alb_count);
 
 		p = detach_one_task(&env);
-		if (p)
+		if (p) {
 			schedstat_inc(sd, alb_pushed);
+			/*
+			 * We want to potentially lower env.src_cpu's OPP.
+			 */
+			update_capacity_of(env.src_cpu);
+		}
 		else
 			schedstat_inc(sd, alb_failed);
 	}