On Fri, Jan 15, 2016 at 09:46:12AM -0800, Paul E. McKenney wrote:

On Fri, Jan 15, 2016 at 10:13:48AM +0100, Peter Zijlstra wrote:

quoted

And the stuff we're confused about is how best to express the difference
and guarantees of these two forms of transitivity and how exactly they
interact.

Hoping my memory-barrier.txt patch helps here...

Yes, that seems a good start. But yesterday you raised the 'fun' point
of two globally ordered sequences connected by a single local link.

And I think I'm still confused on LWSYNC (in the smp_wmb case) when one
of the stores looses a conflict, and if that scenario matters. If it
does, we should inspect the same case for other barriers.