[cpp-threads] Yet another visibility question

[Paul E. McKenney]

On Fri, Jan 12, 2007 at 10:30:46AM +0100, Alexander Terekhov wrote:
> On 1/11/07, Peter Dimov <pdimov at mmltd.net> wrote:
> >Alexander Terekhov wrote:
> >
> >> Yeah, and IBM does some NUMA with Intel Xeons, IIRC. That's why I've
> >> been telling all along that lock_cmpxchg(&var, 42, 42) for loads is
> >> the way to do SC on x86/IA32. ;-)
> >
> >If x86 loads do have acquire semantics as we've been assuming, wouldn't it
> >be enough to just use lock xchg for stores?
> 
> I don't think so. Why would that be enough? Well, actually xchg for
> stores is still needed to ensure leading store-load fencing regarding
> load inside cmpxchg, I think. So for SC on x86/IA32 we need cmpxchg
> for loads and xchg for stores (both locked).

Will this force all stores to independent variables from different
processors to be ordered?  On a large NUMA configuration with multiple
front-side busses?

							Thanx, Paul