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

To: macro@ds2.pg.gda.pl
Subject: Re: [patch] linux 2.4.17: The second mb() rework (final)
From: Atsushi Nemoto <nemoto@toshiba-tops.co.jp>
Date: Thu, 21 Feb 2002 20:41:20 +0900 (JST)
Cc: kevink@mips.com, mdharm@momenco.com, ralf@uni-koblenz.de, linux-mips@fnet.fr, linux-mips@oss.sgi.com
In-reply-to: <Pine.GSO.3.96.1020215125744.29773B-100000@delta.ds2.pg.gda.pl>
Organization: TOSHIBA Personal Computer System Corporation
References: <20020215.123124.70226832.nemoto@toshiba-tops.co.jp> <Pine.GSO.3.96.1020215125744.29773B-100000@delta.ds2.pg.gda.pl>
>>>>> On Fri, 15 Feb 2002 13:08:20 +0100 (MET), "Maciej W. Rozycki" 
>>>>> <macro@ds2.pg.gda.pl> said:
macro> IOW, two consecutive writes separated by a "sync" need not
macro> imply a write-back, but as soon as a read happens a preceding
macro> write-back is a must.

TX39 satisfy this on uncached load/store.  "sync" does not flush a
write buffer, but any uncached load are executed AFTER completion of
pending uncached store.  On combination of cached and uncached
operation, TX39 does not satisfy this order.

macro>  It sounds weird: it looks like "sync" is useless and basically
macro> a "nop".

TX39 has a function called "non-blocking load".  This function is
described on chapter 4.4 of TX39/H2 manual.  "sync" operation is
meaningful with this function.

macro> If this is the case the processors need their own wbflush()
macro> implementation.  Can you point to specific chapters of
macro> specifications that document it?

Chapter 4.9.4 in TX39/H2 Japanese manual describes write buffer.  But
I could not find it in the English manual...

---
Atsushi Nemoto

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