linux-kernel - [PATCH v4 1/7] x86/topology.c: Support functions for BSP online/offline

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Date:	Fri, 11 Nov 2011 21:26:26 -0800
From:	"Fenghua Yu" <fenghua.yu@...el.com>
To:	"Thomas Gleixner" <tglx@...utronix.de>,
	"H Peter Anvin" <hpa@...or.com>, "Ingo Molnar" <mingo@...e.hu>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Tony Luck" <tony.luck@...el.com>,
	"Arjan van de Ven" <arjan.van.de.ven@...el.com>,
	"Suresh B Siddha" <suresh.b.siddha@...el.com>,
	"Len Brown" <len.brown@...el.com>,
	"Randy Dunlap" <rdunlap@...otime.net>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"linux-pm" <linux-pm@...r.kernel.org>, "x86" <x86@...nel.org>,
	"Fenghua Yu" <fenghua.yu@...el.com>
Subject: [PATCH v4 1/7] x86/topology.c: Support functions for BSP online/offline

From: Fenghua Yu <fenghua.yu@...el.com>

By default, BSP can't be hotpluggable because bsp_hotpluggable is 0. Kernel
parameter bsp_hotplug can enable BSP hotplug feature.

Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
---
 arch/x86/kernel/topology.c |   24 +++++++++++++++++-------
 1 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
index 76ee977..4493868 100644
--- a/arch/x86/kernel/topology.c
+++ b/arch/x86/kernel/topology.c
@@ -35,18 +35,28 @@
 static DEFINE_PER_CPU(struct x86_cpu, cpu_devices);
 
 #ifdef CONFIG_HOTPLUG_CPU
+
+static int __read_mostly bsp_hotpluggable;
+
+static int __init enable_bsp_hotplug(char *str)
+{
+	bsp_hotpluggable = 1;
+	return 1;
+}
+
+__setup("bsp_hotplug", enable_bsp_hotplug);
+
 int __ref arch_register_cpu(int num)
 {
 	/*
-	 * CPU0 cannot be offlined due to several
-	 * restrictions and assumptions in kernel. This basically
-	 * doesn't add a control file, one cannot attempt to offline
-	 * BSP.
+	 * Resume from suspend/hibernate depends on BSP. PIC interrupts depend
+	 * on BSP.
 	 *
-	 * Also certain PCI quirks require not to enable hotplug control
-	 * for all CPU's.
+	 * If the BSP depencies are under control, one can tell kernel to
+	 * enable BSP hotplug. This basically adds a control file and
+	 * one can attempt to offline BSP.
 	 */
-	if (num)
+	if (num || bsp_hotpluggable)
 		per_cpu(cpu_devices, num).cpu.hotpluggable = 1;
 
 	return register_cpu(&per_cpu(cpu_devices, num).cpu, num);
-- 
1.6.0.3

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