linux-kernel - Re: [RFC PATCH 1/4] Refcount Based Cpu-Hotplug Implementation

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Message-Id: <20071017042709.02525cbd.pj@sgi.com>
Date:	Wed, 17 Oct 2007 04:27:09 -0700
From:	Paul Jackson <pj@....com>
To:	Paul Jackson <pj@....com>
Cc:	ego@...ibm.com, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	vatsa@...ibm.com, rusty@...tcorp.com.au, dipankar@...ibm.com,
	oleg@...sign.ru, mingo@...e.hu, paulmck@...ibm.com
Subject: Re: [RFC PATCH 1/4] Refcount Based Cpu-Hotplug Implementation

With the following patch, the four cpu hotplug patches by
Gautham R Shenoy boot successfully on my sn2_defconfig ia64
SN2 Altix system.

This patch moves the cpu_hotplug_init() code outside of the
#ifdef CONFIG_HOTPLUG_CPU code.

I will confess to being confused however as to the best way
to handle this.  Having "cpu_hotplug_init" be a piece of code
that has to execute whether or not CONFIG_HOTPLUG_CPU is
enabled doesn't seem right.

Signed-off-by: Paul Jackson <pj@....com>

---

 include/linux/cpu.h |    3 +--
 kernel/cpu.c        |    4 ++--
 2 files changed, 3 insertions(+), 4 deletions(-)

--- 2.6.23-mm1.orig/include/linux/cpu.h	2007-10-17 03:59:59.529623639 -0700
+++ 2.6.23-mm1/include/linux/cpu.h	2007-10-17 04:03:56.257223754 -0700
@@ -83,6 +83,7 @@ static inline void unregister_cpu_notifi
 
 #endif /* CONFIG_SMP */
 extern struct sysdev_class cpu_sysdev_class;
+extern void cpu_hotplug_init(void);
 
 #ifdef CONFIG_HOTPLUG_CPU
 /* Stop CPUs going up and down. */
@@ -97,7 +98,6 @@ static inline void cpuhotplug_mutex_unlo
 	mutex_unlock(cpu_hp_mutex);
 }
 
-extern void cpu_hotplug_init(void);
 extern void get_online_cpus(void);
 extern void put_online_cpus(void);
 #define hotcpu_notifier(fn, pri) {				\
@@ -117,7 +117,6 @@ static inline void cpuhotplug_mutex_lock
 static inline void cpuhotplug_mutex_unlock(struct mutex *cpu_hp_mutex)
 { }
 
-#define cpu_hotplug_init()		do { } while (0)
 #define get_online_cpus()		do { } while (0)
 #define put_online_cpus()		do { } while (0)
 #define hotcpu_notifier(fn, pri)	do { (void)(fn); } while (0)
--- 2.6.23-mm1.orig/kernel/cpu.c	2007-10-17 03:59:59.873628872 -0700
+++ 2.6.23-mm1/kernel/cpu.c	2007-10-17 04:04:52.522079165 -0700
@@ -38,8 +38,6 @@ static struct {
 
 #define writer_exists() (cpu_hotplug.active_writer != NULL)
 
-#ifdef CONFIG_HOTPLUG_CPU
-
 void __init cpu_hotplug_init(void)
 {
 	cpu_hotplug.active_writer = NULL;
@@ -48,6 +46,8 @@ void __init cpu_hotplug_init(void)
 	init_completion(&cpu_hotplug.readers_done);
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+
 void get_online_cpus(void)
 {
 	might_sleep();


-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.925.600.0401
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