linux-kernel - Re: Uses for memory barriers

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Message-Id: <FBEFB0CC-982A-4282-AC37-8EBBC3FDC967@kernel.crashing.org>
Date:	Tue, 12 Sep 2006 19:50:24 +0200
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	paulmck@...ibm.com, David Howells <dhowells@...hat.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: Uses for memory barriers

>> In both cases, the CPU might "discard" the write, if there are no  
>> intervening
>> reads or writes to the same location.  The only difference between  
>> your
>
> How can it know that?

Because it holds the cache line in the "O" (owned) state, for example.

And it doesn't matter how a CPU would do this; the only thing that
matters is that you do not assume anything that is not guaranteed
by the model.


Segher

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