[mpiwg-rma] pirate RMA revisited

[Pavan Balaji]

I’d be opposed to making the standard more assymetric than what it already is.  If you are adding a concept, it should be orthogonal to other functionality.  Number of functions is not the criteria; number of concepts is.

  —- Pavan

On Oct 31, 2013, at 1:40 PM, Jeff Hammond <jeff.science at gmail.com> wrote:

> We've discussed this at MCS coffee hour but I wanted to post to the WG
> regarding the interface issue.
> 
> I understand that the addition of Rrput, Rraccumulate, and
> Rrrget_accumulate (Rget is already fully pirated-out) may be
> unpalatable to some people.
> 
> I propose that we add _only_ Rrrget_accumulate and tell users to
> implement Rrput and Rraccumulate in terms of it using MPI_NO_OP and -
> in the first case - MPI_REPLACE.  The reasoning is by analogy with
> MPI_Alltoallw, which is sufficient to implement MPI_Scatterw, etc.,
> albeit inefficiently.
> 
> If we add only Rrrget_accumulate, the loss of efficiency will be
> comparatively quite small compared to W-collectives (and certainly not
> order-N buffer copies) and should only be due to a few unnecessary
> arguments and a couple of branches, which I argue is not sufficient to
> motivate the addition of two more functions to the standard.  I don't
> believe that users want pirate RMA to optimize for latency...
> 
> Is this reasonable?  I'm hoping to present this at the Chicago Forum
> meeting if the WG believes we are sufficiently converged in our
> thinking.
> 
> Thanks,
> 
> Jeff
> 
> On Sat, Jun 15, 2013 at 9:47 AM, Jim Dinan <james.dinan at gmail.com> wrote:
>> I think the pirate RMA (separate per operation local/remote completion) idea
>> is good.  I'm not sure I'm sold on the interface; I'd rather not add so many
>> new functions, if there's some other way we could do it.  I think we should
>> explore the different design options so that we can verify for the Forum
>> that we've chosen the best one.
> 
> -- 
> Jeff Hammond
> jeff.science at gmail.com
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--
Pavan Balaji
http://www.mcs.anl.gov/~balaji