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: Mon, 29 May 2006 00:38:05 -0700 (PDT)
Organization: Mostly alphabetical, except Q, with we do not fancy
Message-ID: <e5e8ct$bl6$1@terminus.zytor.com>
References: <6gMqr-8uW-23@gated-at.bofh.it> <44779358.9010703@shaw.ca>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7BIT
NNTP-Posting-Date: Mon, 29 May 2006 07:38:05 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1038
Lines: 26

Followup to:  <44779358.9010703@shaw.ca>
By author:    Robert Hancock <hancockr@shaw.ca>
In newsgroup: linux.dev.kernel
> 
> It does seem a little bit less efficient, but I don't know think it's 
> necessarily a bug. There's no guarantee of what size writes will be used 
> with the memcpy_to/fromio functions.
> 

There are only a few semantics that make sense: fixed 8, 16, 32, or 64
bits, plus "optimal"; the latter to be used for anything that doesn't
require a specific transfer size.  Logically, an unqualified
"memcpy_to/fromio" should be the optimal size (as few transfers as
possible) -- we have a qualified "memcpy_to/fromio32" already, and 8-
and 16-bit variants could/should be added.

However, having the unqualified version do byte transfers seems like a
really bad idea.

	-hpa

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/