[RFC][PATCH 0/5] arch: atomic rework

Paul E. McKenney paulmck@linux.vnet.ibm.com
Mon Feb 10 15:06:00 GMT 2014


On Mon, Feb 10, 2014 at 11:49:29AM +0000, Will Deacon wrote:
> On Mon, Feb 10, 2014 at 11:48:13AM +0000, Peter Zijlstra wrote:
> > On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
> > > As near as I can tell, compiler writers hate the idea of prohibiting
> > > speculative-store optimizations because it requires them to introduce
> > > both control and data dependency tracking into their compilers.  Many of
> > > them seem to hate dependency tracking with a purple passion.  At least,
> > > such a hatred would go a long way towards explaining the incomplete
> > > and high-overhead implementations of memory_order_consume, the long
> > > and successful use of idioms based on the memory_order_consume pattern
> > > notwithstanding [*].  ;-)
> > 
> > Just tell them that because the hardware provides control dependencies
> > we actually use and rely on them.
> 
> s/control/address/ ?

Both are important, but as Peter's reply noted, it was control
dependencies under discussion.  Data dependencies (which include the
ARM/PowerPC notion of address dependencies) are called out by the standard
already, but control dependencies are not.  I am not all that satisified
by current implementations of data dependencies, admittedly.  Should
be an interesting discussion.  ;-)

							Thanx, Paul



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