[mpiwg-rma] same_op_no_op

[Balaji, Pavan]

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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