To: linux-kernel@vger.kernel.org
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: memcpy_toio on i386 using byte writes even when n%2==0
Date: Tue, 30 May 2006 18:13:27 -0700 (PDT)
Organization: Mostly alphabetical, except Q, with we do not fancy
Message-ID: <e5iqjn$u22$1@terminus.zytor.com>
References: <6gUec-3mb-7@gated-at.bofh.it> <6icVy-56r-9@gated-at.bofh.it> <6idov-5Tc-7@gated-at.bofh.it> <447CE99B.7070707@shaw.ca>
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Followup to:  <447CE99B.7070707@shaw.ca>
By author:    Robert Hancock <hancockr@shaw.ca>
In newsgroup: linux.dev.kernel
> > 
> > Note that there isn't any code for moving dwords because the
> > chances of gaining anything are slim (alignment may hurt).
> 
> I'd say the chances of gaining something from executing half as many 
> instructions on copying a large block of memory are very good indeed..
> 

For something that generates I/O transactions, it's imperative to
generate the smallest possible number of transactions.  Furthermore,
smaller than dword transactions aren't burstable, except at the
beginning and end of a burst.

	-hpa

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