linux-kernel - Re: Word-at-a-time dcache name accesses (was Re: .. anybody know of any filesystems that depend on the exact VFS 'namehash' implementation?)

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Date:	Fri, 2 Mar 2012 16:17:32 -0800 (PST)
From:	david@...g.hm
To:	"Ted Ts'o" <tytso@....edu>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: Word-at-a-time dcache name accesses (was Re: .. anybody know of
 any filesystems that depend on the exact VFS 'namehash' implementation?)

On Fri, 2 Mar 2012, Ted Ts'o wrote:

> Stupid question.  Your patch requires unaligned accesses to not have a
> heavy penalty, right?  Wasn't it the case that some generations of x86
> had pretty large penalties for aligned accesses?  Is that something we
> need to worry about?

another stupid question

since the code that it's replaceing did byte-at-a-time access, wouldn't 
that be at least as bad as the new code?

or did some CPUs have efficient char access, but inefficient unaligned 
word access?

David Lang
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