sched: fair: placement optimization for heavy load

Previously we have used pure CFS wakeup in overutilized case. This is a
tweaked version to activate the path only for important tasks.

Bug: 161190988
Bug: 160883639
Test: boot and systrace
Signed-off-by: Wei Wang <wvw@google.com>
Signed-off-by: Alexander Winkowski <dereference23@outlook.com>
Change-Id: I2a27f241b3ba32a04cf6f88deb483d6636440dcf

kernel/sched/fair.c

@@ -7711,6 +7711,13 @@ static inline int find_best_target(struct task_struct *p, int *backup_cpu,
 				if (best_idle_cpu != -1)
 					continue;
 
+				/*
+				 * Skip searching for active CPU for tasks have
+				 * high priority & stune.boost.
+				 */
+				if (boosted && p->prio <= DEFAULT_PRIO)
+					continue;
+
 				/*
 				 * Case A.2: Target ACTIVE CPU
 				 * Favor CPUs with max spare capacity.
@@ -7938,7 +7945,9 @@ static inline int find_best_target(struct task_struct *p, int *backup_cpu,
 #ifdef CONFIG_SCHED_WALT
 	if (target_cpu == -1 && most_spare_cap_cpu != -1 &&
 		/* ensure we use active cpu for active migration */
-		!(p->state == TASK_RUNNING && !idle_cpu(most_spare_cap_cpu)))
+		!(p->state == TASK_RUNNING && !idle_cpu(most_spare_cap_cpu)) &&
+		/* do not pick an overutilized most_spare_cap_cpu */
+		!cpu_overutilized(most_spare_cap_cpu))
 		target_cpu = most_spare_cap_cpu;
 #endif