Re: Does Itanium permit speculative stores?

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Tue, Nov 26, 2013 at 11:55:58PM -0500, Jon Masters wrote:
> On 11/11/2013 12:13 PM, Paul E. McKenney wrote:
> > Hello, Tony,
> > 
> > Does Itanium permit speculative stores?  For example, on Itanium what are
> > the permitted outcomes of the following litmus test, where both x and y
> > are initially zero?
> > 
> > 	CPU 0				CPU 1
> > 
> > 	r1 = ACCESS_ONCE(x);		r2 = ACCESS_ONCE(y);
> > 	if (r1)				if (r2)
> > 		ACCESS_ONCE(y) = 1;		ACCESS_ONCE(x) = 1;
> > 
> > In particular, is the outcome (r1 == 1 && r2 == 1) possible on Itanium
> > given this litmus test?
> > 
> > 							Thanx, Paul
> > 
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> 
> Btw, I was reading through some UEFI docs and noticed a reference to "A
> Formal Specification of Intel Itanium Processor Family Memory Ordering",
> then remembered this thread. In case it's of use:
> 
> http://www.intel.com/design/itanium/downloads/251429.htm

I have seen this, but there have been too many times when I have fooled
myself about what the words mean (with DEC Alpha back in the late 90s
being the most impressive example).  So while I do learn what I can from
them, they are unfortunately not a substitute for asking.  ;-)

Besides, some of the Itanium locking code uses instructions that the
above manual is silent about.

							Thanx, Paul