linux-kernel - Re: [rfc][patch] i386: remove comment about barriers

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Date:	Sat, 29 Sep 2007 12:12:52 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Nick Piggin <npiggin@...e.de>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Paul McKenney <paulmck@...ibm.com>,
	David Howells <dhowells@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...e.de>
Subject: Re: [rfc][patch] i386: remove comment about barriers

On Sat, 29 Sep 2007, Nick Piggin wrote:

> [ This is true for x86's sfence/lfence, but raises a question about Linux's
> memory barriers. Does anybody expect that a sequence of smp_wmb and smp_rmb
> would ever provide a full smp_mb barrier? I've always assumed no, but I
> don't know if it is actually documented? ]

No, that can't be. rmb+wmb can't be considered a full mb. There was a 
recent discussion about this in the thread originated by peterz scalable 
rw_mutex patches.



- Davide


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