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

On Wed, Aug 15, 2007 at 08:51:58PM +0200, Segher Boessenkool wrote:

quoted

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.

						Thanx, Paul

quoted

Consider that smp_rmb basically will do anything from flushing the
pipeline to invalidating loads speculatively executed out of order. 
AFAIK
it will not control the visibility of stores coming from other CPUs 
(that
is up to the cache coherency).

The writer side should typically use wmb() whenever the reader side
uses rmb(), sure.


Segher

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