[Mpi3-hybridpm] [Mpi3-rma] Fix for win_allocate_shared

[Pavan Balaji]

Ok, I understand your disagreement. We should discuss this in the telecon.

  -- Pavan

On 09/23/2011 12:59 PM, Barrett, Brian W wrote:
> I disagree. It provides a rational target for future architectures and provides the ability of all cache coherent systems to support shared memory, something I'm not convinced the unified model does.
>
> Brian
>
> ----- Original Message -----
> From: Pavan Balaji [mailto:balaji at mcs.anl.gov]
> Sent: Friday, September 23, 2011 11:56 AM
> To: mpi3-rma at lists.mpi-forum.org<mpi3-rma at lists.mpi-forum.org>
> Cc: Barrett, Brian W; Torsten Hoefler<htor at illinois.edu>; mpi3-hybridpm at lists.mpi-forum.org<mpi3-hybridpm at lists.mpi-forum.org>
> Subject: Re: [Mpi3-rma] Fix for win_allocate_shared
>
>
> On 09/23/2011 12:47 PM, Barrett, Brian W wrote:
>> It might not be able to. If non-coherent load/store is byte access
>> (or word access), it can provide a separate public and private window
>> in separate and meet the semantics.  If it provides cacheline access
>> to non-coherent space, it will not be able to provide shared memory
>> across uncached space; such is the cost of standardization.
>
> Do we know any non-cache-coherent system that provides byte access (note
> that word access is not sufficient)?
>
> What I'm arguing is that we are not giving any additional flexibility
> for non-cache-coherent systems with this new "clarified semantics". In
> fact, we are making it more difficult for future MPI versions to
> actually define a semantics by saying that "multiple remote stores to
> the same window have to work" -- we'll be stuck with this if we say that
> in the standard now.
>
> Instead, if we leave it undefined, in MPI-3.1 (or 4.0), we might be able
> to separate out local load/store and remote load/store operations and
> say that multiple remote load/store operations is undefined (or
> erroneous or whatever).
>
> So the options I'm proposing are:
>
> 1. Either define remote load/stores in SEPARATE.
>
> (or)
>
> 2. Leave it as undefined.
>
> Attempting a half-definition is making it worse than leaving it undefined.
>
>    -- Pavan
>

-- 
Pavan Balaji
http://www.mcs.anl.gov/~balaji