linux-kernel - Re: [PATCH 6/24] make atomic_read() behave consistently on frv

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Message-ID: <46C3A675.7050108@yahoo.com.au>
Date:	Thu, 16 Aug 2007 11:20:53 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Segher Boessenkool <segher@...nel.crashing.org>
CC:	paulmck@...ux.vnet.ibm.com, heiko.carstens@...ibm.com,
	horms@...ge.net.au, linux-kernel@...r.kernel.org,
	rpjday@...dspring.com, ak@...e.de, netdev@...r.kernel.org,
	cfriesen@...tel.com, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, linux-arch@...r.kernel.org,
	jesper.juhl@...il.com, zlynx@....org, schwidefsky@...ibm.com,
	Chris Snook <csnook@...hat.com>, davem@...emloft.net,
	wensong@...ux-vs.org, wjiang@...ilience.com,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 6/24] make atomic_read() behave consistently on frv

Segher Boessenkool wrote:
>> Please check the definition of "cache coherence".
> 
> 
> Which of the twelve thousand such definitions?  :-)

Every definition I have seen says that writes to a single memory
location have a serial order as seen by all CPUs, and that a read
will return the most recent write in the sequence (with a bit of
extra mumbo jumbo to cover store queues and store forwarding).

Within such a definition, I don't see how would be allowed for a
single CPU to execute reads out of order and have the second read
return an earlier write than the first read.

-- 
SUSE Labs, Novell Inc.
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