linux-kernel - Re: [PATCH] x86/copy_user_generic: Optimize copy_user

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Date:	Thu, 24 May 2012 21:50:19 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	fenghua.yu@...el.com
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	andi@...stfloor.org, linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86/copy_user_generic: Optimize copy_user_generic with
 CPU erms feature

From: "Fenghua Yu" <fenghua.yu@...el.com>
Date: Thu, 24 May 2012 18:19:45 -0700

> According to Intel 64 and IA-32 SDM and Optimization Reference
> Manual, beginning with Ivybridge, REG string operation using MOVSB
> and STOSB can provide both flexible and high-performance REG string
> operations in cases like memory copy.  Enhancement availability is
> indicated by CPUID.7.0.EBX[9] (Enhanced REP MOVSB/ STOSB).

How does the cpu do overlap detection?

If the cpu does overlap detection on sub-pagesize bits, performance
will unnecessarily suffer under such circumstances.
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