[mpiwg-rma] same_op_no_op

[Jeff Hammond]

Does this or does this not break BW compatibility w.r.t. MPI-2.2 and
did we do it intentionally?  Unless we did so intentionally and
explicitly, I will argue that the WG screwed up and the info key+val
is invalid.

Jeff

On Mon, Mar 10, 2014 at 11:03 PM, Balaji, Pavan <balaji at anl.gov> wrote:
>
> If a hardware can implement MPI_SUM, it should be able to implement MPI_SUM with 0 as well.
>
> But that’s not a generic solution.
>
> Jeff: at some point you were planning to bring in a ticket which does more combinations of operations than just same_op and no_op.  Maybe it’s worthwhile bringing that up again?
>
>   — Pavan
>
> On Mar 10, 2014, at 9:26 PM, Jim Dinan <james.dinan at gmail.com> wrote:
>
>> Maybe there's a loophole that I'm forgetting?
>>
>>
>> On Mon, Mar 10, 2014 at 9:43 PM, Jeff Hammond <jeff.science at gmail.com> wrote:
>> How the hell can I do GA or SHMEM then? Roll my own mutexes and commit perf-suicide?
>>
>> Jeff
>>
>> Sent from my iPhone
>>
>> On Mar 10, 2014, at 8:32 PM, Jim Dinan <james.dinan at gmail.com> wrote:
>>
>>> You can't use replace and sum concurrently at a given target address.
>>>
>>>  ~Jim.
>>>
>>> On Mon, Mar 10, 2014 at 4:30 PM, Jeff Hammond <jeff.science at gmail.com> wrote:
>>> Given the following, how do I use MPI_NO_OP, MPI_REPLACE and MPI_SUM
>>> in accumulate/atomic operations in a standard-compliant way?
>>>
>>> accumulate_ops — if set to same_op, the implementation will assume
>>> that all concurrent accumulate calls to the same target address will
>>> use the same operation. If set to same_op_no_op, then the
>>> implementation will assume that all concurrent accumulate calls to the
>>> same target address will use the same operation or MPI_NO_OP. This can
>>> eliminate the need to protect access for certain operation types where
>>> the hardware can guarantee atomicity. The default is same_op_no_op.
>>>
>>> We discuss this before and the resolution was not satisfying to me.
>>>
>>> Thanks,
>>>
>>> Jeff
>>>
>>> --
>>> Jeff Hammond
>>> jeff.science at gmail.com
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-- 
Jeff Hammond
jeff.science at gmail.com