[mpich-discuss] Using __float128 with MPI_Accumulate()?

[Pavan Balaji]

I meant predefined datatype, not OP.  I believe the limitation in this 
particular case is not the operations, just the datatypes, anyway.

  -- Pavan

On 12/25/2011 09:34 PM, Pavan Balaji wrote:
>
> On 12/25/2011 09:23 PM, Jeff Hammond wrote:
>> The primary reason that the MPI standard does not allow user-defined
>> reductions for MPI_Accumulate is not the nature of floating-point
>> types, but rather the operations themselves, since user-defined
>> accumulate is equivalent to active-messages, which cannot be
>> implemented in hardware.  Of course, __float128 is not supported by
>> any hardware I know of, but neither is complex double, but the Forum
>> found a way to let that one slide.
>
> The concern was not that there currently doesn't exist hardware to do an
> operation X (say complex double), but rather that it's not possible to
> build hardware that does arbitrary user-defined operations.
>
> The easiest way for this is to get float128 defined as a predefined OP
> in MPI.  We added a bunch in MPI-2.2.  It should be fairly
> straightforward to add more even in 3.0 if we can get the text written
> up before this Forum and in time for a formal reading.  If not, 3.1
> should definitely be possible.
>
>    -- Pavan
>

-- 
Pavan Balaji
http://www.mcs.anl.gov/~balaji