Re: [PATCH 6/24] make atomic_read() behave consistently on frv

Paul E. McKenney
2007-08-15T19:59:55Z

On Wed, Aug 15, 2007 at 09:46:55PM +0200, Segher Boessenkool wrote:
> >>>Well if there is only one memory location involved, then smp_rmb()
> >>>isn't
> >>>going to really do anything anyway, so it would be incorrect to use
> >>>it.
> >>
> >>rmb() orders *any* two reads; that includes two reads from the same
> >>location.
> >
> >If the two reads are to the same location, all CPUs I am aware of
> >will maintain the ordering without need for a memory barrier.
>
> That's true of course, although there is no real guarantee for that.

A CPU that did not provide this property ("cache coherence") would be
most emphatically reviled. So we are pretty safe assuming that CPUs
will provide it.

Thanx, Paul