linux-kernel - Re: [patch] x86: Fix incorrect __read_mostly on _boot_cpu

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Date:	Wed, 31 Dec 2008 14:18:17 -0800
From:	Mike Travis <travis@....com>
To:	Ravikiran G Thirumalai <kiran@...lex86.org>
CC:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [patch] x86: Fix incorrect __read_mostly on _boot_cpu_pda

Ravikiran G Thirumalai wrote:
> The pda rework (commit 3461b0af025251bbc6b3d56c821c6ac2de6f7209)
> to remove static boot cpu pdas introduced a bug.  _boot_cpu_pda is the
> actual pda used by the boot cpu and is definitely not "__read_mostly" and
> ended up polluting the read mostly section with writes.  This bug caused
> regression of about 8-10% on certain syscall intensive workloads.
> 
> Signed-off-by: Ravikiran Thirumalai <kiran@...lex86.org>
> 
> Index: linux-2.6/arch/x86/kernel/head64.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/head64.c	2008-12-30 15:28:08.000000000 -0800
> +++ linux-2.6/arch/x86/kernel/head64.c	2008-12-31 10:36:21.000000000 -0800
> @@ -27,7 +27,7 @@
>  #include <asm/trampoline.h>
>  
>  /* boot cpu pda */
> -static struct x8664_pda _boot_cpu_pda __read_mostly;
> +static struct x8664_pda _boot_cpu_pda;
>  
>  #ifdef CONFIG_SMP
>  /*

Thanks for catching that!

Mike
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