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From: Arnd Bergmann <arnd@arndb.de>
To: paulmck@linux.vnet.ibm.com
Subject: Re: [PATCH 6/24] make atomic_read() behave consistently on frv
Date: Wed, 15 Aug 2007 15:29:43 +0200
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On Wednesday 15 August 2007, Paul E. McKenney wrote:

> ACCESS_ONCE() is indeed intended to be used when actually loading or
> storing the variable.  That said, I must admit that it is not clear to me
> why you would want to add an extra order() rather than ACCESS_ONCE()ing
> one or both of the adjacent accesses to that same variable.
> 
> So, what am I missing?

You're probably right, the only case I can construct is something like

	if (ACCESS_ONCE(x)) {
		...
		ACCESS_ONCE(x)++;
	}

which would be slightly less efficient than

	if (x)
		x++;
	order(x);

because in the first case, you need to do two ordered accesses
but only one in the second case. However, I can't think of a case
where this actually makes a noticable difference in real life.

	Arnd <><
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