linux-kernel - Re: [PATCH v3 1/7] x86/topology.c: Support functions for BSP online/offline

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Date:	Fri, 11 Nov 2011 13:23:28 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Fenghua Yu <fenghua.yu@...el.com>
Cc:	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>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v3 1/7] x86/topology.c: Support functions for BSP
 online/offline

On Wed, Nov 09, 2011 at 04:34:11PM -0800, Fenghua Yu wrote:
> 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..a3fc939 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 bsp_hotpluggable;

__read_mostly

> +
> +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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