[mpiwg-rma] [EXTERNAL] Re: same_op_no_op and SHMEM

[Barrett, Brian W]

I would have no objection to adding yet another info key.  I think if we
keep at this for another year, we can make sure we have the longest
pre-defined info key in the spec.

I admit to having very little medium term memory; which is the
type-homogeneity suggestion?

Brian


On 10/24/13 12:53 PM, "Jeff Hammond" <jeff.science at gmail.com> wrote:

>Honestly, I think REPLACE+NO_OP is a useful option, I just think
>REPLACE+NO_OP+<SUM or ...> is _also_ a useful option.  Why don't we
>just turn our frowns upside down and add this to the standard?
>
>Does anyone object to info = same_op_no_op_replace?
>
>I would appreciate any feedback on my type-homogeneity suggestion as
>well.  Do people agree that is worth adding?  I imagine that there is
>hardware that can do e.g. sum+long but not sum+double, especially if
>it has to be atomic.
>
>Jeff
>
>On Thu, Oct 24, 2013 at 1:46 PM, Barrett, Brian W <bwbarre at sandia.gov>
>wrote:
>> Or "I will only do gets and compare-and-swap", which is something a
>>couple
>> of graph codes I've looked at do.  But I agree, we probably should have
>> made it REPLACE, NO_OP, and 1 other op or not added it at all.  Sigh :).
>>
>> Brian
>>
>> On 10/24/13 11:39 AM, "Jeff Hammond" <jeff.science at gmail.com> wrote:
>>
>>>I read same_op_no_op as "I will use only MPI_REPLACE and MPI_NO_OP"
>>>i.e. give me nothing more than atomic Put/Get, I do not want to
>>>actually accumulate anything.
>>>
>>>Jeff
>>>
>>>On Thu, Oct 24, 2013 at 12:34 PM, Underwood, Keith D
>>><keith.d.underwood at intel.com> wrote:
>>>> Yes, that's the motivation, but I'm not sure if anybody does atomics
>>>>without puts....  It seems to me like we should have included
>>>>MPI_REPLACE in that list
>>>>
>>>>> -----Original Message-----
>>>>> From: mpiwg-rma [mailto:mpiwg-rma-bounces at lists.mpi-forum.org] On
>>>>> Behalf Of Pavan Balaji
>>>>> Sent: Thursday, October 24, 2013 1:33 PM
>>>>> To: MPI WG Remote Memory Access working group
>>>>> Subject: Re: [mpiwg-rma] same_op_no_op and SHMEM
>>>>>
>>>>>
>>>>> The motivation was that it's hard to maintain atomicity when
>>>>>different
>>>>> operations are done.  For example, if the hardware only supports some
>>>>> atomic operations, but not all, this might result in some operations
>>>>> happening in hardware and some in software making atomicity hard.  In
>>>>>such
>>>>> cases, the MPI implementation might need to fall back to
>>>>>software-only
>>>>> implementations.
>>>>>
>>>>>   -- Pavan
>>>>>
>>>>> On Oct 24, 2013, at 12:23 PM, Jeff Hammond <jeff.science at gmail.com>
>>>>> wrote:
>>>>>
>>>>> > I recall that Brian and/or Keith wanted same_op_no_op because of
>>>>> > SHMEM.  However, SHMEM requires the use of MPI_NO_OP (for atomic
>>>>> Get
>>>>> > via Get_accumulate), MPI_REPLACE (for atomic Put via Accumulate)
>>>>>and
>>>>> > MPI_SUM (for add, fadd, inc and finc).  So what is the benefit of
>>>>> > same_op_no_op to SHMEM?  Perhaps I remember completely wrong and
>>>>> the
>>>>> > motivation was something that does not use the latter atomics.  Or
>>>>> > perhaps it is common for SHMEM codes to not use these and thus the
>>>>> > assumption is MPI_SUM can be ignored.
>>>>> >
>>>>> > Jeff
>>>>> >
>>>>> > --
>>>>> > Jeff Hammond
>>>>> > jeff.science at gmail.com
>>>>> > _______________________________________________
>>>>> > mpiwg-rma mailing list
>>>>> > 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
>>>>>
>>>>> _______________________________________________
>>>>> mpiwg-rma mailing list
>>>>> mpiwg-rma at lists.mpi-forum.org
>>>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
>>>> _______________________________________________
>>>> mpiwg-rma mailing list
>>>> mpiwg-rma at lists.mpi-forum.org
>>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
>>>
>>>
>>>
>>>--
>>>Jeff Hammond
>>>jeff.science at gmail.com
>>>_______________________________________________
>>>mpiwg-rma mailing list
>>>mpiwg-rma at lists.mpi-forum.org
>>>http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
>>>
>>
>>
>> --
>>   Brian W. Barrett
>>   Scalable System Software Group
>>   Sandia National Laboratories
>>
>>
>>
>>
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>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
>
>
>
>-- 
>Jeff Hammond
>jeff.science at gmail.com
>_______________________________________________
>mpiwg-rma mailing list
>mpiwg-rma at lists.mpi-forum.org
>http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
>


--
  Brian W. Barrett
  Scalable System Software Group
  Sandia National Laboratories