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Date: Thu, 9 Feb 2012 09:06:48 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Borislav Petkov <bp@alien8.de>, Nick Bowler <nbowler@elliptictech.com>,
        Randy Dunlap <rdunlap@xenotime.net>, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>,
        Kevin Winchester <kjwinchester@gmail.com>
Subject: Re: MCE, AMD: Hide smp-only code around CONFIG_SMP
Message-ID: <20120209080648.GI18387@elte.hu>
References: <1328209817-18913-1-git-send-email-bp@alien8.de>
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* Borislav Petkov <bp@alien8.de> wrote:

> +++ b/arch/x86/include/asm/smp.h
> @@ -33,8 +33,15 @@ static inline bool cpu_has_ht_siblings(void)
>  
>  DECLARE_PER_CPU(cpumask_var_t, cpu_sibling_map);
>  DECLARE_PER_CPU(cpumask_var_t, cpu_core_map);
> -/* cpus sharing the last level cache: */
> +
> +#ifdef CONFIG_SMP
> +/* CPUs sharing the last level cache: */
>  DECLARE_PER_CPU(cpumask_var_t, cpu_llc_shared_map);
> +#else
> +static DECLARE_BITMAP(cpu_llc_shared_bits, NR_CPUS) __read_mostly = { [0] = 1UL };
> +static struct cpumask *const cpu_llc_shared_map = to_cpumask(cpu_llc_shared_bits);
> +#endif

Why not just expose it like on SMP?

We want to *reduce* the specialness of UP, not increase it - one 
more word of .data and .text does not matter much - UP is 
becoming more and more an oddball, rarely tested config. By the 
time these changes hit any real boxes it will be even more 
oddball.

Thanks,

	Ingo