linux-kernel - [PATCH 35/38] tick-broadcast: do checks before taking locks in tick_do_broadcast_on

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Message-Id: <6dd682c8bb0c56f0b40a4ff5ca94acfb536b109f.1397492345.git.viresh.kumar@linaro.org>
Date:	Mon, 14 Apr 2014 21:53:57 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	tglx@...utronix.de
Cc:	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, Arvind.Chauhan@....com,
	linaro-networking@...aro.org,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: [PATCH 35/38] tick-broadcast: do checks before taking locks in tick_do_broadcast_on_off()

Some of the checks which may force tick_do_broadcast_on_off() to return early
can be done before taking locks. This would make these codepaths faster.

Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 kernel/time/tick-broadcast.c | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 1597d03..3b07569 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -329,27 +329,22 @@ unlock:
  */
 static void tick_do_broadcast_on_off(unsigned long *reason)
 {
-	struct clock_event_device *bc, *dev;
-	struct tick_device *td;
+	struct tick_device *td = tick_get_cpu_device();
+	struct clock_event_device *bc, *dev = td->evtdev;
+	int cpu = smp_processor_id(), bc_stopped;
 	unsigned long flags;
-	int cpu, bc_stopped;
-
-	raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
-
-	cpu = smp_processor_id();
-	td = tick_get_device(cpu);
-	dev = td->evtdev;
-	bc = tick_broadcast_device.evtdev;
 
 	/*
 	 * Is the device not affected by the powerstate ?
 	 */
 	if (!dev || !(dev->features & CLOCK_EVT_FEAT_C3STOP))
-		goto out;
+		return;
 
 	if (!tick_device_is_functional(dev))
-		goto out;
+		return;
 
+	raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
+	bc = tick_broadcast_device.evtdev;
 	bc_stopped = cpumask_empty(tick_broadcast_mask);
 
 	switch (*reason) {
@@ -385,7 +380,6 @@ static void tick_do_broadcast_on_off(unsigned long *reason)
 		else
 			tick_broadcast_setup_oneshot(bc);
 	}
-out:
 	raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
 }
 
-- 
1.7.12.rc2.18.g61b472e

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