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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: Fri, 15 Feb 2002 13:08:20 +0100 (MET)
Cc: kevink@mips.com, mdharm@momenco.com, ralf@uni-koblenz.de, linux-mips@fnet.fr, linux-mips@oss.sgi.com
In-reply-to: <20020215.123124.70226832.nemoto@toshiba-tops.co.jp>
Organization: Technical University of Gdansk
Sender: owner-linux-mips@oss.sgi.com
On Fri, 15 Feb 2002, Atsushi Nemoto wrote:

> Note that SYNC on TX39/H and TX39/H2 does not flush a write buffer.

 That's perfectly fine -- it does not need to.  It's only a
synchronization point.

> Some operation (for example, bc0f loop) are required to flush a write
> buffer.

 This is bad, though.  No extra operations must be needed.  After a "sync" 
the buffer should be written back as soon as not doing so would be visible
externally.  IOW, two consecutive writes separated by a "sync" need not
imply a write-back, but as soon as a read happens a preceding write-back
is a must.

 It sounds weird: it looks like "sync" is useless and basically a "nop". 
If this is the case the processors need their own wbflush()
implementation.  Can you point to specific chapters of specifications that
document it?

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


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