From: Srinath Sridharan <srinathsr@google.com>
Date: Fri, 29 Jul 2016 16:50:11 +0000 (+0100)
Subject: sched/fair: Favor higher cpus only for boosted tasks
X-Git-Tag: firefly_0821_release~176^2~195
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=bfa1dd2bfda910b60e425974fd5dc94a6bdaccc4;p=firefly-linux-kernel-4.4.55.git

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 88eae79d1a3c..e7f9afe29c61 100644
--- 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))