linux-kernel - Re: [PATCH v4 6/8] x86/ftrace: Use __pa_symbol instead of _

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Date:	Fri, 16 Nov 2012 15:06:03 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Alexander Duyck <alexander.h.duyck@...el.com>, tglx@...utronix.de,
	mingo@...hat.com, andi@...stfloor.org,
	Frederic Weisbecker <fweisbec@...il.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 6/8] x86/ftrace: Use __pa_symbol instead of __pa on
 C visible symbols

On 11/16/2012 02:45 PM, Steven Rostedt wrote:
>
> #define __pa(x)		__phys_addr((unsigned long)(x))
> #define __pa_symbol(x)	__pa(__phys_reloc_hide((unsigned long)(x)))
>
> I'm confused. __pa_symbol() just calls __pa() with some macro magic to
> its parameter. How is this a performance improvement?
>

One of the earlier patches in this series changes __pa_symbol() to avoid 
the conditional hidden inside __phys_addr(), since by definition a 
symbol can only be on one side of that branch.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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