sched/fair: Favor higher cpus only for boosted tasks

This CL separates the notion of boost and prefer_idle schedtune
attributes in cpu selection. Today only top-app
tasks are boosted. The CPU selection is slightly tweaked such that
higher order cpus are preferred only for boosted tasks (top-app) and the
rest would be skewed towards lower order cpus.
This avoids starvation issues for fg tasks when interacting with high
priority top-app tasks (a problem often seen in the case of system_server).

bug: 30245369
bug: 30292998
Change-Id: I0377e00893b9f6586eec55632a265518fd2fa8a1

Conflicts:
	kernel/sched/fair.c

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 88eae79d1a3cd49f0c58017c079d07b6fda338bc..e7f9afe29c61a1af8d5b406c9e321897a04635e0 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5612,7 +5612,7 @@ done:
        return target;
 }
 
-static inline int find_best_target(struct task_struct *p, bool prefer_idle)
+static inline int find_best_target(struct task_struct *p, bool boosted, bool prefer_idle)
 {
        int iter_cpu;
        int target_cpu = -1;
@@ -5630,9 +5630,9 @@ static inline int find_best_target(struct task_struct *p, bool prefer_idle)
                int idle_idx;
 
                /*
-                * favor higher cpus for tasks that prefer idle cores
+                * Iterate from higher cpus for boosted tasks.
                 */
-               int i = prefer_idle ? NR_CPUS-iter_cpu-1 : iter_cpu;
+               int i = boosted ? NR_CPUS-iter_cpu-1 : iter_cpu;
 
                if (!cpu_online(i) || !cpumask_test_cpu(i, tsk_cpus_allowed(p)))
                        continue;
@@ -5802,7 +5802,7 @@ static int energy_aware_wake_cpu(struct task_struct *p, int target, int sync)
                bool boosted = 0;
                bool prefer_idle = 0;
 #endif
-               int tmp_target = find_best_target(p, boosted || prefer_idle);
+               int tmp_target = find_best_target(p, boosted, prefer_idle);
                if (tmp_target >= 0) {
                        target_cpu = tmp_target;
                        if ((boosted || prefer_idle) && idle_cpu(target_cpu))