linux-kernel - [PATCH 08/14] sched: trig ILB on an idle buddy

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Message-Id: <1366910611-20048-9-git-send-email-vincent.guittot@linaro.org>
Date:	Thu, 25 Apr 2013 19:23:24 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, peterz@...radead.org,
	mingo@...nel.org, linux@....linux.org.uk, pjt@...gle.com,
	santosh.shilimkar@...com, Morten.Rasmussen@....com,
	chander.kashyap@...aro.org, cmetcalf@...era.com,
	tony.luck@...el.com, alex.shi@...el.com, preeti@...ux.vnet.ibm.com
Cc:	paulmck@...ux.vnet.ibm.com, tglx@...utronix.de,
	len.brown@...el.com, arjan@...ux.intel.com,
	amit.kucheria@...aro.org, corbet@....net, l.majewski@...sung.com,
	Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 08/14] sched: trig ILB on an idle buddy

If the buddy CPU is not full and currently idle, we trigger an Idle Load
Balance to give it the opportunity to pull more tasks.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 874f330..954adfd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5776,6 +5776,26 @@ end:
 	clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
 }
 
+static int check_nohz_buddy(int cpu)
+{
+	int buddy = per_cpu(sd_pack_buddy, cpu);
+
+	if (sysctl_sched_packing_mode != SCHED_PACKING_FULL)
+		return false;
+
+	/* No pack buddy for this CPU */
+	if (buddy == -1)
+		return false;
+
+	if (is_buddy_full(buddy))
+		return false;
+
+	if (cpumask_test_cpu(buddy, nohz.idle_cpus_mask))
+		return true;
+
+	return false;
+}
+
 /*
  * Current heuristic for kicking the idle load balancer in the presence
  * of an idle cpu is the system.
@@ -5813,6 +5833,10 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu)
 	if (rq->nr_running >= 2)
 		goto need_kick;
 
+	/* the buddy is idle and not busy so we can pack */
+	if (check_nohz_buddy(cpu))
+		goto need_kick;
+
 	rcu_read_lock();
 	for_each_domain(cpu, sd) {
 		struct sched_group *sg = sd->groups;
-- 
1.7.9.5

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