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Date:   Fri, 15 Jan 2016 09:55:54 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
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Subject: Re: [v3,11/41] mips: reuse asm-generic/barrier.h
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On Thu, Jan 14, 2016 at 01:29:13PM -0800, Paul E. McKenney wrote:
> So smp_mb() provides transitivity, as do pairs of smp_store_release()
> and smp_read_acquire(), 

But they provide different grades of transitivity, which is where all
the confusion lays.

smp_mb() is strongly/globally transitive, all CPUs will agree on the order.

Whereas the RCpc release+acquire is weakly so, only the two cpus
involved in the handover will agree on the order.