linux-kernel - [PATCH 1/4] Move C3 stop test outside lock

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Date:	Fri,  6 May 2011 14:40:53 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH 1/4] Move C3 stop test outside lock

From: Andi Kleen <ak@...ux.intel.com>

Avoid taking locks in the idle path for systems where the timer
doesn't stop in C3.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 kernel/time/tick-broadcast.c |   11 ++++-------
 1 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index da800ff..2fc424d 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -456,23 +456,22 @@ void tick_broadcast_oneshot_control(unsigned long reason)
 	unsigned long flags;
 	int cpu;
 
-	raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
-
 	/*
 	 * Periodic mode does not care about the enter/exit of power
 	 * states
 	 */
 	if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
-		goto out;
+		return;
 
-	bc = tick_broadcast_device.evtdev;
 	cpu = smp_processor_id();
+	bc = tick_broadcast_device.evtdev;
 	td = &per_cpu(tick_cpu_device, cpu);
 	dev = td->evtdev;
 
 	if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
-		goto out;
+		return;
 
+	raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
 	if (reason == CLOCK_EVT_NOTIFY_BROADCAST_ENTER) {
 		if (!cpumask_test_cpu(cpu, tick_get_broadcast_oneshot_mask())) {
 			cpumask_set_cpu(cpu, tick_get_broadcast_oneshot_mask());
@@ -489,8 +488,6 @@ void tick_broadcast_oneshot_control(unsigned long reason)
 				tick_program_event(dev->next_event, 1);
 		}
 	}
-
-out:
 	raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
 }
 
-- 
1.7.4.4

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