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From: Ingo Molnar <mingo@elte.hu>
To: Andi Kleen <andi@firstfloor.org>
Cc: "Yu, Fenghua" <fenghua.yu@intel.com>,
	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
Date: Wed, 18 May 2011 20:47:03 +0200	[thread overview]
Message-ID: <20110518184703.GB6225@elte.hu> (raw)
In-Reply-To: <20110518183913.GA12317@one.firstfloor.org>

* Andi Kleen <andi@firstfloor.org> wrote:

> > 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.

Well, your generic, vague claims about what GCC could possibly do does not 
count much when weighted against the hard data he provided.

He used a defconfig and reported his results and has proven that your claim is 
wrong in fairly common circumstances.

If you think the result is or should be different provide a config and test it 
yourself, contradicting/countering the data he provided.

Thanks,

	Ingo

  reply	other threads:[~2011-05-18 18:47 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-05-17 22:29 [PATCH 0/9] Optimize string operations " Fenghua Yu
2011-05-17 22:29 ` [PATCH 1/9] x86, cpu: Enable enhanced REP MOVSB/STOSB feature Fenghua Yu
2011-05-17 23:13   ` [tip:x86/cpufeature] x86, cpufeature: Add CPU feature bit for enhanced REP MOVSB/STOSB tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 2/9] x86/kernel/cpu/intel.c: Initialize Enhanced REP MOVSB/STOSBenhanced Fenghua Yu
2011-05-18  2:46   ` Andi Kleen
2011-05-18  3:47     ` H. Peter Anvin
2011-05-18 20:40   ` [tip:perf/core] x86, mem, intel: Initialize Enhanced REP MOVSB/STOSB tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 3/9] x86/kernel/alternative.c: Add comment for applying alternatives order Fenghua Yu
2011-05-18 20:40   ` [tip:perf/core] x86, alternative, doc: " tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 4/9] x86, alternative-asm.h: Add altinstruction_entry macro Fenghua Yu
2011-05-18 20:41   ` [tip:perf/core] x86, alternative: " tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 5/9] x86/lib/clear_page_64.S: Support clear_page() with enhanced REP MOVSB/STOSB Fenghua Yu
2011-05-18 20:41   ` [tip:perf/core] x86, mem: clear_page_64.S: " tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 6/9] x86/lib/copy_user_64.S: Support copy_to_user/copy_from_user by " Fenghua Yu
2011-05-18 20:42   ` [tip:perf/core] x86, mem: copy_user_64.S: Support copy_to/from_user " tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 7/9] x86/lib/memcpy_64.S: Optimize memcpy " Fenghua Yu
2011-05-18  6:35   ` Ingo Molnar
2011-05-18 19:04     ` Yu, Fenghua
2011-05-18 20:42   ` [tip:perf/core] x86, mem: memcpy_64.S: " tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 8/9] x86/lib/memmove_64.S: Optimize memmove " Fenghua Yu
2011-05-18 20:43   ` [tip:perf/core] x86, mem: memmove_64.S: " tip-bot for Fenghua Yu
2011-05-17 22:29 ` [PATCH 9/9] x86/lib/memset_64.S: Optimize memset " Fenghua Yu
2011-05-18  2:57   ` Andi Kleen
2011-05-18  3:09     ` Yu, Fenghua
2011-05-18  4:05       ` Andi Kleen
2011-05-18 18:33         ` Yu, Fenghua
2011-05-18 18:39           ` Andi Kleen
2011-05-18 18:47             ` Ingo Molnar [this message]
2011-05-18 18:49             ` Yu, Fenghua
2011-05-18 20:43   ` [tip:perf/core] x86, mem: memset_64.S: " tip-bot for Fenghua Yu

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