perf events ring buffer memory barrier on powerpc

[Paul E. McKenney]

On Mon, Oct 28, 2013 at 10:58:58PM +0200, Victor Kaplansky wrote:
> Oleg Nesterov <oleg at 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