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From: David Howells <dhowells@redhat.com>
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Subject: Re: Memory barriers and spin_unlock safety 
Date: Fri, 03 Mar 2006 20:17:07 +0000
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To: Linus Torvalds <torvalds@osdl.org>
Cc: David Howells <dhowells@redhat.com>, akpm@osdl.org, ak@suse.de, mingo@redhat.com, jblunck@suse.de, bcrl@linux.intel.com, matthew@wil.cx, linux-arch@vger.kernel.org, linuxppc64-dev@ozlabs.org, linux-kernel@vger.kernel.org
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Linus Torvalds <torvalds@osdl.org> wrote:

> Note that _normal_ writes never need an SFENCE, because they are ordered 
> by the core.
> 
> The reason to use SFENCE is because of _special_ writes.

I suspect, then, that x86_64 should not have an SFENCE for smp_wmb(), and that
only io_wmb() should have that.

David