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Date: Thu, 25 Feb 2016 06:08:16 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Jianyu Zhan <nasa4836@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
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Subject: Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency
 and identical stores
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On Thu, Feb 25, 2016 at 02:41:07PM +0800, Jianyu Zhan wrote:
> On Thu, Feb 25, 2016 at 5:40 AM, Paul E. McKenney
> <paulmck@linux.vnet.ibm.com> wrote:
> > So ordering between the read from "a" and the write to "b" is still
> > preserved.  The reason this works is that the smp_mb() does all the
> > ordering, so the fact that the control dependency has been eliminated
> > is irrelevant.
> 
> 
> Thanks, Paul,  nice clarification.
> 
> I thinks this example qualifies as an good example to demonstrate the subtle
> scope of effect of these two level barriers.
> 
> A vivid example is always better for understanding instead of learning
> "barrier() is compiler-level
> barrier, and smp_*mb() is processor-level barrier" by rote ,
> especially for the new comers to memory-barriers.txt. ;-)

Glad you like it.  ;-)

							Thanx, Paul