On Wed, 15 Aug 2007, Paul E. McKenney wrote:

Understood.  My point is not that the impact is precisely zero, but
rather that the impact on optimization is much less hurtful than the
problems that could arise otherwise, particularly as compilers become
more aggressive in their optimizations.

The problems arise because barriers are not used as required. Volatile 
has wishy washy semantics and somehow marries memory barriers with data 
access. It is clearer to separate the two. Conceptual cleanness usually 
translates into better code. If one really wants the volatile then lets 
make it explicit and use

	atomic_read_volatile()