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Date: Wed, 18 May 2011 20:39:13 +0200
From: Andi Kleen <andi@firstfloor.org>
To: "Yu, Fenghua" <fenghua.yu@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>, Ingo Molnar <mingo@elte.hu>,
        Thomas Gleixner <tglx@linutronix.de>, H Peter Anvin <hpa@zytor.com>,
        "Mallick, Asit K" <asit.k.mallick@intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Avi Kivity <avi@redhat.com>, Arjan van de Ven <arjan@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 9/9] x86/lib/memset_64.S: Optimize memset by enhanced REP MOVSB/STOSB
Message-ID: <20110518183913.GA12317@one.firstfloor.org>
References: <1305671358-14478-1-git-send-email-fenghua.yu@intel.com> <1305671358-14478-10-git-send-email-fenghua.yu@intel.com> <08d8c27c0495452cad52b62b362dd1d1.squirrel@www.firstfloor.org> <493994B35A117E4F832F97C4719C4C04011505C39D@orsmsx505.amr.corp.intel.com> <9317a84b59d0a78a4b8e304ac2da490a.squirrel@www.firstfloor.org> <493994B35A117E4F832F97C4719C4C04011505C7DC@orsmsx505.amr.corp.intel.com>
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> 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@linux.intel.com -- Speaking for myself only.