linux-kernel - Re: idle issues running sembench on 128 cpus II

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Date:	Thu, 5 May 2011 01:48:06 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Dave Kleikamp <dkleikamp@...il.com>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, lenb@...nel.org, paulmck@...ibm.com
Subject: Re: idle issues running sembench on 128 cpus II

> Here's a new patch without the raw. Boots on my Westmere.

Sorry appended the old patch. Here's really the new version.

From: Andi Kleen <ak@...ux.intel.com>
Date: Wed, 4 May 2011 15:09:27 -0700
Subject: [PATCH] Move C3 stop test outside lock

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>

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index da800ff..7f565b7 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());

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