linux-kernel - Re: [PATCH 7/9] x86/topology.c: Support functions for BSP online/offline

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Date:	Sun, 06 Nov 2011 02:43:41 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.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>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Len Brown <len.brown@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linux PM mailing list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 7/9] x86/topology.c: Support functions for BSP online/offline

On 11/05/2011 03:33 AM, 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.
> 
> arch_cpu_maps_update_begin() and arch_cpu_maps_update_done() locks/unlocks
> pm_mutex. This solves cpu maps race condition between BSP online check during
> hibernate/suspend and BSP online/offline operations.
> 
> arch_state_check() checks if BSP is still the first online CPU.
> 
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> ---
>  arch/x86/kernel/topology.c |   44 +++++++++++++++++++++++++++++++++++++-------
>  1 files changed, 37 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
> index 8927486..287d7b6 100644
> --- a/arch/x86/kernel/topology.c
> +++ b/arch/x86/kernel/topology.c
> @@ -29,23 +29,53 @@
>  #include <linux/mmzone.h>
>  #include <linux/init.h>
>  #include <linux/smp.h>
> +#include <linux/suspend.h>
>  #include <asm/cpu.h>
> 
>  static DEFINE_PER_CPU(struct x86_cpu, cpu_devices);
> 
>  #ifdef CONFIG_HOTPLUG_CPU
> +
> +static int bsp_hotpluggable;
> +
> +static int __init enable_bsp_hotplug(char *str)
> +{
> +	bsp_hotpluggable = 1;
> +	return 0;

Any reason why you return 0 here? Most code I have seen similar to this,
return 1. I understand that anything declared using early_param() would
generate a warning if it returns non-zero, but I am not exactly sure
about how it behaves with __setup(). Kindly give this some thought.

> +}
> +
> +__setup("bsp_hotplug", enable_bsp_hotplug);
> +

Thanks,
Srivatsa S. Bhat

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