linux-kernel - Re: [PATCH v2 2/2] x86: Added read_mostly declaration/definition to vars from smp.h

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Message-ID: <20120518081416.GA20872@gmail.com>
Date:	Fri, 18 May 2012 10:14:16 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Vlad Zolotarov <vlad@...lemp.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Shai Fultheim (Shai@...leMP.com)" <Shai@...lemp.com>
Subject: Re: [PATCH v2 2/2] x86: Added read_mostly declaration/definition to
 vars from smp.h


* Vlad Zolotarov <vlad@...lemp.com> wrote:

> Added a "read-mostly" qualifier to the following variables in smp.h:
>  - cpu_sibling_map
>  - cpu_core_map
>  - cpu_llc_shared_map
>  - cpu_llc_id
>  - cpu_number
>  - x86_cpu_to_apicid
>  - x86_bios_cpu_apicid
>  - x86_cpu_to_logical_apicid
> 
> As long as all the variables above are only written during the initialization,
> this change is meant to prevent the false sharing and improve the
> performance on large multiprocessor systems.
> 
> Signed-off-by: Vlad Zolotarov <vlad@...lemp.com>
> Signed-off-by: Shai Fultheim <shai@...lemp.com>
> ---
>  arch/x86/include/asm/apic.h    |    2 +-
>  arch/x86/include/asm/smp.h     |   16 ++++++++--------
>  arch/x86/kernel/apic/apic.c    |    6 +++---
>  arch/x86/kernel/setup_percpu.c |    2 +-
>  arch/x86/kernel/smpboot.c      |    8 ++++----
>  5 files changed, 17 insertions(+), 17 deletions(-)


This does not build on !SMP kernels that has APIC enabled.

Thanks,

	Ingo
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