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Re: [patch] linux 2.4.17: The second mb() rework (final)

To: Atsushi Nemoto <nemoto@toshiba-tops.co.jp>
Subject: Re: [patch] linux 2.4.17: The second mb() rework (final)
From: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>
Date: Thu, 21 Feb 2002 15:19:25 +0100 (MET)
Cc: jgg@debian.org, kevink@mips.com, linux-mips@fnet.fr, linux-mips@oss.sgi.com
In-reply-to: <20020221.210052.38718643.nemoto@toshiba-tops.co.jp>
Organization: Technical University of Gdansk
Sender: owner-linux-mips@oss.sgi.com
On Thu, 21 Feb 2002, Atsushi Nemoto wrote:

> As I wrote in another mail, TX39's uncached load does NOT return data
> from a write buffer.  Uncached load/store always appears on I/O bus in
> same order.

 Well, the specification suggests that a load doesn't stall until all data
from the buffer are written back.  Therefore a load will appear on the
host bus before pending writes.  It implies mb() has to stall on the
"buffer not empty" condition.

> The problem of TX39's write buffer is that cached load/store operation
> can overtake preceding uncached store operation (even if "SYNC" was
> exist between these operations).

 It's implied by the above.

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +


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