linux-kernel - Re: [PATCH 9/9] x86/lib/memset_64.S: Optimize memset by enhanced REP MOVSB/STOSB

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Message-ID: <20110518183913.GA12317@one.firstfloor.org>
Date:	Wed, 18 May 2011 20:39:13 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Yu, Fenghua" <fenghua.yu@...el.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	H Peter Anvin <hpa@...or.com>,
	"Mallick, Asit K" <asit.k.mallick@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Avi Kivity <avi@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 9/9] x86/lib/memset_64.S: Optimize memset by enhanced REP MOVSB/STOSB

> I use gcc 4.3.2 installed by FC10 to build kernel with defconfig. Only memcpy is built with gcc builtin and inline memcpy. All of others (i.e. memset, clear_page, memmove, and copy_user) call the kernel lib.
> 
> It's easy to check this by disassembling kernel binary.

gcc has a complex set of heuristics. For example if it cannot decide
the length or the alignment it calls the kernel code. Otherwise
it inlines.

So just looking at a few examples won't give you the whole picture.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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