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Re: Promblem with PREF (prefetching) in memcpy

To: "Kevin D. Kissell" <kevink@mips.com>
Subject: Re: Promblem with PREF (prefetching) in memcpy
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
Date: 04 Oct 2002 14:15:30 +0100
Cc: Carsten Langgaard <carstenl@mips.com>, Dominic Sweetman <dom@algor.co.uk>, Ralf Baechle <ralf@linux-mips.org>, linux-mips@linux-mips.org
In-reply-to: <00fe01c26ba6$04943480$10eca8c0@grendel>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <3D9D484B.4C149BD8@mips.com><200210041153.MAA12052@mudchute.algor.co.uk> <3D9D855B.12128FA2@mips.com> <1033734968.31839.5.camel@irongate.swansea.linux.org.uk> <00fe01c26ba6$04943480$10eca8c0@grendel>
Sender: linux-mips-bounce@linux-mips.org
On Fri, 2002-10-04 at 14:00, Kevin D. Kissell wrote:
> The issue isn't that anyone would deliberately use memcpy() in I/O
> space.  Rather, it's that memcpy() prefetches quite a ways ahead,
> and if one has I/O space assigned just after the end of physical
> memory, Bad Things might happen on a perfectly legal memcpy()
> that references the last couple hundred bytes of memory in a 
> way that not even a clever and well-informed bus error handler 
> could undo.

Then your memcpy function is IMHO broken. Fix it to note prefetch beyond
the end of the area you actually will copy and life should be a lot
better


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