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Date: Tue, 7 Nov 2006 19:54:30 -0800
From: Andrew Morton <akpm@osdl.org>
To: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Cc: ak@suse.de, shaohua.li@intel.com, linux-kernel@vger.kernel.org,
       discuss@x86-64.org, ashok.raj@intel.com
Subject: Re: [patch 2/4] introduce the mechanism of disabling cpu hotplug
 control
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On Tue, 7 Nov 2006 17:40:25 -0800
"Siddha, Suresh B" <suresh.b.siddha@intel.com> wrote:

> Add 'cpu_hotplug_no_control' and when set, the hotplug control file("online")
> will not be added under /sys/devices/system/cpu/cpuX/
> 
> Next patch doing PCI quirks will use this.
> 

I don't understand what this (ugly) patch has to do with the overall
bugfix.  We're fixing the APCI initialisation - what does that have to do
with presenting cpu-hotplug files in sysfs?


> ---
> 
> diff --git a/arch/i386/kernel/topology.c b/arch/i386/kernel/topology.c
> index 07d6da3..9b766e7 100644
> --- a/arch/i386/kernel/topology.c
> +++ b/arch/i386/kernel/topology.c
> @@ -40,14 +40,22 @@ int arch_register_cpu(int num)
>  	 * restrictions and assumptions in kernel. This basically
>  	 * doesnt add a control file, one cannot attempt to offline
>  	 * BSP.
> +	 *
> +	 * Also certain PCI quirks require to remove this control file
> +	 * for all CPU's.
>  	 */
> +#ifdef CONFIG_HOTPLUG_CPU
> +	if (!num || cpu_hotplug_no_control)
> +#else
>  	if (!num)
> +#endif

This ifdef could be removed 

>  		cpu_devices[num].cpu.no_control = 1;
>  
>  	return register_cpu(&cpu_devices[num].cpu, num);
>  }
>  
>  #ifdef CONFIG_HOTPLUG_CPU
> +int cpu_hotplug_no_control;
>  
>  void arch_unregister_cpu(int num) {
>  	return unregister_cpu(&cpu_devices[num].cpu);
> diff --git a/include/asm-i386/cpu.h b/include/asm-i386/cpu.h
> index b1bc7b1..3c5da33 100644
> --- a/include/asm-i386/cpu.h
> +++ b/include/asm-i386/cpu.h
> @@ -13,6 +13,7 @@ struct i386_cpu {
>  extern int arch_register_cpu(int num);
>  #ifdef CONFIG_HOTPLUG_CPU
>  extern void arch_unregister_cpu(int);
> +extern int cpu_hotplug_no_control;

via:

#else
#define cpu_hotplug_no_control 1

here.


But does this variable _have_ to be a negative like this?  The code would
be simpler if it had the opposite sense and was called, say,
cpu_hotplug_enable_control_file.

Are these patches considered 2.6.19 material?  They look a bit big, ugly
and scary for that.