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

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Message-ID: <46BCC26B.6080600@redhat.com>
Date:	Fri, 10 Aug 2007 15:54:19 -0400
From:	Chris Snook <csnook@...hat.com>
To:	David Howells <dhowells@...hat.com>
CC:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	torvalds@...ux-foundation.org, netdev@...r.kernel.org,
	akpm@...ux-foundation.org, ak@...e.de, heiko.carstens@...ibm.com,
	davem@...emloft.net, schwidefsky@...ibm.com, wensong@...ux-vs.org,
	horms@...ge.net.au, wjiang@...ilience.com, cfriesen@...tel.com,
	zlynx@....org, rpjday@...dspring.com, jesper.juhl@...il.com
Subject: Re: [PATCH 6/24] make atomic_read() behave consistently on frv

David Howells wrote:
> Chris Snook <csnook@...hat.com> wrote:
> 
>> To head off the criticism, I admit this is an oversimplification, and true
>> busy-waiters should be using cpu_relax(), which contains a barrier.
> 
> Why would you want to use cpu_relax()?  That's there to waste time efficiently,
> isn't it?  Shouldn't you be using smp_rmb() or something like that?
> 
> David

cpu_relax() contains a barrier, so it should do the right thing.  For 
non-smp architectures, I'm concerned about interacting with interrupt 
handlers.  Some drivers do use atomic_* operations.

	-- Chris
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