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Date: Wed, 30 Oct 2013 02:27:25 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Victor Kaplansky <VICTORK@il.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Anton Blanchard <anton@samba.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux PPC dev <linuxppc-dev@ozlabs.org>,
        Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
        Michael Ellerman <michael@ellerman.id.au>,
        Michael Neuling <mikey@neuling.org>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: perf events ring buffer memory barrier on powerpc
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On Mon, Oct 28, 2013 at 10:58:58PM +0200, Victor Kaplansky wrote:
> Oleg Nesterov <oleg@redhat.com> wrote on 10/28/2013 10:17:35 PM:
> 
> >       mb();   // XXXXXXXX: do we really need it? I think yes.
> 
> Oh, it is hard to argue with feelings. Also, it is easy to be on
> conservative side and put the barrier here just in case.
> But I still insist that the barrier is redundant in your example.

If you were to back up that insistence with a description of the orderings
you are relying on, why other orderings are not important, and how the
important orderings are enforced, I might be tempted to pay attention
to your opinion.

							Thanx, Paul