perf events ring buffer memory barrier on powerpc

[Peter Zijlstra]

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.

I'll make it a full mb for now and too am curious to see the end of this
discussion explaining things ;-)