linux-kernel - Re: [PATCH 1/2] x86, percpu: Optimize this_cpu

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Message-ID: <4C8360ED.8070700@kernel.org>
Date:	Sun, 05 Sep 2010 11:20:45 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Brian Gerst <brgerst@...il.com>
CC:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86, percpu: Optimize this_cpu_ptr

Hello,

On 09/04/2010 07:21 PM, Brian Gerst wrote:
> diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
> index cd28f9a..d854438 100644
> --- a/arch/x86/include/asm/percpu.h
> +++ b/arch/x86/include/asm/percpu.h
> @@ -47,6 +47,15 @@
>  #ifdef CONFIG_SMP
>  #define __percpu_arg(x)		"%%"__stringify(__percpu_seg)":%P" #x
>  #define __my_cpu_offset		percpu_read(this_cpu_off)
> +#define __this_cpu_ptr(ptr)				\
> +({							\
> +	typeof(ptr) __ptr = (ptr);			\
> +	__verify_pcpu_ptr(ptr);				\
> +	asm volatile("add " __percpu_arg(1) ", %0"	\
> +		     : "+r" (__ptr)			\
> +		     : "m" (this_cpu_off));		\
> +	__ptr;						\
> +}) 

Great, thanks for doing this, but can you please comment on what
__this_cpu_ptr() optimizes above?  Something similar to the patch
description but shorter.

Thanks.

-- 
tejun
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