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Re: Prefetches in memcpy

To: "Kevin D. Kissell" <kevink@mips.com>
Subject: Re: Prefetches in memcpy
From: Ralf Baechle <ralf@linux-mips.org>
Date: Tue, 5 Nov 2002 17:41:02 +0100
Cc: Carsten Langgaard <carstenl@mips.com>, linux-mips@linux-mips.org
In-reply-to: <00fb01c284e6$5b7bf4f0$10eca8c0@grendel>; from kevink@mips.com on Tue, Nov 05, 2002 at 05:13:48PM +0100
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <3DC7CB8B.E2C1D4E5@mips.com> <20021105163806.A24996@bacchus.dhis.org> <00fb01c284e6$5b7bf4f0$10eca8c0@grendel>
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On Tue, Nov 05, 2002 at 05:13:48PM +0100, Kevin D. Kissell wrote:

> >  - Avoid prefetching beyond the end of the copy area in memcpy and memmove.
> >  - Introduce a second variant of memcpy that never does prefetching.  This
> >    one will be safe to use in KSEG1 / uncached XKPHYS also and will be used
> >    for memcpy_fromio, memcpy_toio and friends.
> 
> Assuming we had a version that prefetched exactly to the end
> of the source memory block and no further, why would we need
> the second variant?

Uh...  Maybe missread your mail the first time.  We're also prefechting
the destination area, of course with a different hint.  The question is
what the hints for destination are actually doing, the specs are fairly
vague on that and seem to leave the decission to the implementor.  Do
we really want to try ...

  Ralf

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