[mpiwg-rma] pirate RMA revisited

[Jeff Hammond]

Okay, I have no problem with adding all the pirate RMA functions -
Rrput, Rraccumulate and Rrrget_accumulate - but I wanted to throw this
out for discussion.  I will create a ticket for this now for tracking
purposes.

I look forward to your ticket proposing {Scatter,Gather,Allgather}w
(and the nonblocking and neighborhood variants) to give the MPI
standard the symmetry it deserves :-)

Jeff

On Thu, Oct 31, 2013 at 1:46 PM, Pavan Balaji <balaji at mcs.anl.gov> wrote:
>
> 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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>> mpiwg-rma at lists.mpi-forum.org
>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
>
> --
> Pavan Balaji
> http://www.mcs.anl.gov/~balaji
>
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> mpiwg-rma at lists.mpi-forum.org
> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma



-- 
Jeff Hammond
jeff.science at gmail.com