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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: Fri, 22 Feb 2002 11:36:34 +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.3.96.1020221143103.1033G-100000@delta.ds2.pg.gda.pl>
Organization: TOSHIBA Personal Computer System Corporation
References: <20020221.204120.102764790.nemoto@toshiba-tops.co.jp> <Pine.GSO.3.96.1020221143103.1033G-100000@delta.ds2.pg.gda.pl>
>>>>> On Thu, 21 Feb 2002 15:12:43 +0100 (MET), "Maciej W. Rozycki" 
>>>>> <macro@ds2.pg.gda.pl> said:
macro>  With respect to cache refills (what is already cached is
macro> irrelevant, obviously, as read accesse to it don't appear
macro> externally), "32-bit RISC Microprocessor TX39 Family Core
macro> Architecture User's Manual" seems to contradict.  In the
macro> description of the "sync" instruction it states:

macro> "Interlocks the pipeline until the load, store or data cache
macro> refill operation of the previous instruction is completed.  The
macro> R3900 Processor Core can continue processing instructions
macro> following a load instruction even if a cache refill is caused
macro> by the load instruction or a load is made from a noncacheable
macro> area.  Executing a SYNC instruction interlocks subsequent
macro> instructions until the SYNC instruction execution is completed.
macro> This ensures that the instructions following a load instruction
macro> are executed in the proper sequence."

The contradiction is came from some confusion about usage of a word
"Core" in TX39 manual.  Maybe a writer of the quoted statements
assumes a write buffer is outside of a "R3900 Processor Core".  So if
he said "operation is completed" it means "data are sent to a write
buffer".  Of course this point of view is not acceptable for software
programmers...

macro> It's clear "sync" is strong on the TX39, stronger then required
macro> by MIPS II.

So unfortunately this is not true.

---
Atsushi Nemoto

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