sched: Avoid unnecessary load balance when tasks don't fit on dst_cpu

When considering to pull over a task that does not fit on the
destination CPU make sure that the busiest group has exceeded its
capacity. While the change is applicable to all groups, the biggest
impact will be on migrating big tasks to little CPUs. This should
only happen when the big cluster is no longer capable of balancing
load within the cluster. This change should have no impact on single
cluster systems.

Change-Id: I6d1ef0e0d878460530f036921ce4a4a9c1e1394b
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>

1 files changed, 25 insertions, 8 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0ae7c75fffc7..087f5e072e35 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3578,6 +3578,11 @@ static inline int nr_big_tasks(struct rq *rq)
 
 #define sched_enable_power_aware 0
 
+static inline int task_will_fit(struct task_struct *p, int cpu)
+{
+	return 1;
+}
+
 static inline int select_best_cpu(struct task_struct *p, int target, int reason)
 {
 	return 0;
@@ -6766,6 +6771,8 @@ struct lb_env {
 	long			imbalance;
 	/* The set of CPUs under consideration for load-balancing */
 	struct cpumask		*cpus;
+	unsigned int		busiest_grp_capacity;
+	unsigned int		busiest_nr_running;
 
 	unsigned int		flags;
 
@@ -6896,6 +6903,10 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
 	if (env->flags & LBF_IGNORE_SMALL_TASKS && is_small_task(p))
 		return 0;
 
+	if (!task_will_fit(p, env->dst_cpu) &&
+			env->busiest_nr_running <= env->busiest_grp_capacity)
+		return 0;
+
 	if (!cpumask_test_cpu(env->dst_cpu, tsk_cpus_allowed(p))) {
 		int cpu;
 
@@ -7819,6 +7830,8 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
 		if (update_sd_pick_busiest(env, sds, sg, sgs)) {
 			sds->busiest = sg;
 			sds->busiest_stat = *sgs;
+			env->busiest_nr_running = sgs->sum_nr_running;
+			env->busiest_grp_capacity = sgs->group_capacity;
 		}
 
 next_group:
@@ -8349,6 +8362,8 @@ static int load_balance(int this_cpu, struct rq *this_rq,
 		.imbalance	= 0,
 		.flags		= 0,
 		.loop		= 0,
+		.busiest_nr_running     = 0,
+		.busiest_grp_capacity   = 0,
 	};
 
 	/*
@@ -8796,14 +8811,16 @@ static int active_load_balance_cpu_stop(void *data)
 	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,
-		.flags		= 0,
-		.loop		= 0,
+		.sd			= sd,
+		.dst_cpu		= target_cpu,
+		.dst_rq			= target_rq,
+		.src_cpu		= busiest_rq->cpu,
+		.src_rq			= busiest_rq,
+		.idle			= CPU_IDLE,
+		.busiest_nr_running 	= 0,
+		.busiest_grp_capacity 	= 0,
+		.flags			= 0,
+		.loop			= 0,
 	};
 	bool moved = false;