[Mpi3-rma] Alternative Proposal for Shared Memory Support

[Rajeev Thakur]

That's what I meant in my first mail. We need to say whether this example will work or not.

A=10
barrier         barrier
                    x = A

If not, which synchronization functions need to be used and how? The current text does not automatically cover this example.

Rajeev


On Mar 15, 2011, at 9:28 PM, Torsten Hoefler wrote:

> On Tue, Mar 15, 2011 at 09:22:49PM -0500, Rajeev Thakur wrote:
>> All can be used, but none are needed, right?
> We might need to talk about synch or flush. Some shared memory systems
> are loosely coupled and need membars to guarantee correct ordering. 
> 
>> Currently, in the unified model you can do:
>> 
>> lock
>> put(A)
>> unlock
>> barrier          barrier
>>                      x = A
>> 
>> With shared memory, you could do
>> 
>> A=10
>> barrier         barrier
>>                     x = A
>> 
>> Right?
> Not really. The barrier and the x=A might be re-ordered. This is also
> the biggest issue with our definition of the unified model, some shared
> memory systems might actually not be able to support it :-(. We had a
> long discussion in Stuttgart about this.
> 
>> If the above is true, it might be a bit confusing to users that in the
>> RMA chapter you use put, get, and synchronization functions for some
>> things and can directly read/write memory for some other things.
> Well, the standard is not a user documentation :-). But yes, having this
> special kind of window requires some effort to understand it.
> 
> Best,
>  Torsten
> 
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