linux-kernel - Re: [patch] x86, mm: pass in 'total' to __copy_from_user

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Message-ID: <49AB648B.5090302@zytor.com>
Date:	Sun, 01 Mar 2009 20:46:03 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
CC:	Arjan van de Ven <arjan@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	David Miller <davem@...emloft.net>,
	torvalds@...ux-foundation.org, mingo@...e.hu, sqazi@...gle.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: [patch] x86, mm: pass in 'total' to __copy_from_user_*nocache()

Nick Piggin wrote:
> 
> I would expect any high performance CPU these days to combine entries
> in the store queue, even for normal store instructions (especially for
> linear memcpy patterns). Isn't this likely to be the case?
> 

Actually, that is often not the case simply because it doesn't buy that
much.  The big win comes when you don't read a whole cache line in from
memory, but that is a property of the cache, not the store queue.

	-hpa

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

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