linux-kernel - [PATCH v2 3/3] sched/balance: remove on_null_domain() in trigger_load

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Date:	Fri, 14 Sep 2012 13:47:25 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	mingo@...hat.com, peterz@...radead.org, tglx@...utronix.de,
	suresh.b.siddha@...el.com, venki@...gle.com
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/3] sched/balance: remove on_null_domain() in trigger_load_balance

According to Suresh's inverstigation, the first on_null_domain in
trigger_load_balance is for avoiding unnecessary loadbalances(from
softirq) when a SMP kernel running on UP machine.
The second on_null_domain is not needed, since nohz_kick_needed()
will return 0 in this scenario.

So, remove the 2nd on_null_domain calling.

Signed-off-by: Alex Shi <alex.shi@...el.com>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 60d5505..1ae2c66 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4938,7 +4938,7 @@ void trigger_load_balance(struct rq *rq, int cpu)
 	    likely(!on_null_domain(cpu)))
 		raise_softirq(SCHED_SOFTIRQ);
 #ifdef CONFIG_NO_HZ
-	if (nohz_kick_needed(rq, cpu) && likely(!on_null_domain(cpu)))
+	if (nohz_kick_needed(rq, cpu))
 		nohz_balancer_kick(cpu);
 #endif
 }
-- 
1.7.12

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