linux-kernel - [patch v3 8/8] sched: use instant load for burst wake up

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Date:	Tue,  2 Apr 2013 11:23:28 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	mingo@...hat.com, peterz@...radead.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, arjan@...ux.intel.com, bp@...en8.de,
	pjt@...gle.com, namhyung@...nel.org, efault@....de,
	morten.rasmussen@....com
Cc:	vincent.guittot@...aro.org, gregkh@...uxfoundation.org,
	preeti@...ux.vnet.ibm.com, viresh.kumar@...aro.org,
	linux-kernel@...r.kernel.org, alex.shi@...el.com,
	len.brown@...el.com, rafael.j.wysocki@...el.com, jkosina@...e.cz,
	clark.williams@...il.com, tony.luck@...el.com,
	keescook@...omium.org, mgorman@...e.de, riel@...hat.com
Subject: [patch v3 8/8] sched: use instant load for burst wake up

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@...el.com>
---
 kernel/sched/fair.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fdb88de..c2f6e4e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3103,12 +3103,26 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
 	unsigned long weight;
 	int balanced;
 	int runnable_avg;
+	int burst_prev = 0, burst_this = 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)
+		burst_this = 1;
+	if (cpu_rq(prev_cpu)->avg_idle < sysctl_sched_migration_cost)
+		burst_prev = 1;
+
+	/* use instant load on bursty waking up cpu */
+	if (!burst_prev)
+		load = source_load(prev_cpu, idx);
+	else
+		load = cpu_rq(prev_cpu)->load.weight;
+	if (!burst_this)
+		this_load = target_load(this_cpu, idx);
+	else
+		this_load = cpu_rq(this_cpu)->load.weight;
 
 	/*
 	 * If sync wakeup then subtract the (maximum possible)
-- 
1.7.12

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