[PATCH] sched: use instant load for burst wake up

[Alex Shi]

If many tasks sleep long time, their runnable load are zero. And if they
are waked up bursty, too light runnable load causes big imbalance among
CPU. So such benchmark, like aim9 drop 5~7%.

With this patch the losing is covered, and even is slight better.

Signed-off-by: Alex Shi <alex.shi@xxxxxxxxx>
---
 kernel/sched/fair.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index dbaa8ca..25ac437 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3103,12 +3103,24 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
 	unsigned long weight;
 	int balanced;
 	int runnable_avg;
+	int burst = 0;
 
 	idx	  = sd->wake_idx;
 	this_cpu  = smp_processor_id();
 	prev_cpu  = task_cpu(p);
-	load	  = source_load(prev_cpu, idx);
-	this_load = target_load(this_cpu, idx);
+
+	if (cpu_rq(this_cpu)->avg_idle < sysctl_sched_migration_cost ||
+		cpu_rq(prev_cpu)->avg_idle < sysctl_sched_migration_cost)
+		burst= 1;
+
+	/* use instant load for bursty waking up */
+	if (!burst) {
+		load = source_load(prev_cpu, idx);
+		this_load = target_load(this_cpu, idx);
+	} else {
+		load = cpu_rq(prev_cpu)->load.weight;
+		this_load = cpu_rq(this_cpu)->load.weight;
+	}
 
 	/*
 	 * If sync wakeup then subtract the (maximum possible)
-- 
1.7.12

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