[Mpi-forum] MPI_Type_create_struct vs. other datatype creation routines

[Mohamad Chaarawi]

Hi Fab,

On 08/29/2011 02:29 PM, Fab Tillier wrote:
> Mohamad Chaarawi wrote on Mon, 29 Aug 2011 at 12:08:49
>
>> Hi Fab,
>>
>> On 08/29/2011 01:58 PM, Fab Tillier wrote:
>>> Pavan Balaji wrote on Mon, 29 Aug 2011 at 07:21:32
>>>
>>>> Great. We have a use case for this as well, and we are essentially doing
>>>> exactly what you are doing. Are you planning to do a formal reading for
>>>> it at the next meeting?
>>>>
>>>> Btw, hindexed is not a real replacement for indexed as the MPI
>>>> implementation can be better optimized for indexed than hindexed (e.g.,
>>>> alignment checks). So the right solution would have been to allow
>>>> indexed to take MPI_Aint arguments as well. But given that the
>>>> performance difference would be so small, I'm not sure if we should
>>>> create yet another set of routines for it.
>>> IMO, there should be MPI_Count versions of all the datatype constructors,
>>> and the existing ones deprecated.  I thought there was some work to that
>>> effect going on.  That's not to say I wouldn't want to see hindexed_block in
>>> the standard, I'd just rather it used MPI_Count than MPI_Aint...
>>>
>> I though datatype creation (and several other) functions that use int s
>> for the count should have MPI_Count versions, but the H versions, that
>> use byte displacements, should still use MPI_Aint, because it's not
>> really a count of datatypes, but just an offset into memory.
> Datatypes may represent data on a file, not just in memory.  How do you express an offset (byte displacement) in a file, when that offset can be larger than what can be represented by MPI_Aint?

yea ok.. so you're saying MPI_Count should be able to handle large 
counts of oldtype, and large addresses into memory (MPI_Aint) and file 
(MPI_Offset). I though MPI_Count was just to handle larger than 32 bit 
integer count of "oldtypes".

Mohamad

> Cheers,
> -Fab
>
>> Mohamad
>>
>>> -Fab
>>>
>>>>     -- Pavan
>>>> On 08/29/2011 07:55 AM, Mohamad Chaarawi wrote:
>>>>> Hi Pavan,
>>>>>
>>>>> actually I created a ticket for that about a month ago, #280 :)
>>>>> https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/280
>>>>>
>>>>> we have a usecase were we use hindexed for MPI_Aint displacement, but
>>>>> we really need 1 block length, so we end up passing an array of 1s :(
>>>>>
>>>>> Thanks,
>>>>> Mohamad
>>>>>
>>>>> On 08/27/2011 08:34 PM, Pavan Balaji wrote:
>>>>>> Ok, that makes sense. It would have been good if the ones where
>>>>>> offsets are specified in datatype lengths also took MPI_Aint, to allow
>>>>>> for MPI_BOTTOM.
>>>>>>
>>>>>> Using hindexed instead of indexed would have been OK, except the MPI
>>>>>> implementation can optimize alignment checks for indexed (by
>>>>>> checking only the first element), but can't do that for hindexed.
>>>>>>
>>>>>> Also, are we missing hindexed_block in the standard?
>>>>>>
>>>>>>     -- Pavan
>>>>>> On 08/27/2011 10:04 AM, Rajeev Thakur wrote:
>>>>>>> If the displacement is specified in multiples of the extent of
>>>>>>> oldtype, it is defined as int. If the displacement is specified in
>>>>>>> bytes it is defined as Aint.
>>>>>>>
>>>>>>> Rajeev
>>>>>>>
>>>>>>>
>>>>>>> On Aug 27, 2011, at 7:08 AM, William Gropp wrote:
>>>>>>>
>>>>>>>> Look at the Fortran binding - to create Fortran interfaces that
>>>>>>>> used MPI_ADDRESS_KIND, we first had to *have* an MPI_ADDRESS_KIND,
>>>>>>>> which is possible in Fortran 90 and later.  MPI-1 could only
>>>>>>>> provide a Fortran 77 binding.
>>>>>>>>
>>>>>>>> Bill
>>>>>>>>
>>>>>>>> On Aug 27, 2011, at 6:03 AM, Pavan Balaji wrote:
>>>>>>>>
>>>>>>>>> No, that can't be right.
>>>>>>>>>
>>>>>>>>> MPI_Type_hindexed was in MPI-1, and it had MPI_Aint for
>>>>>>>>> displacement.
>>>>>>>>>
>>>>>>>>> MPI_Type_indexed on the other hand uses int.
>>>>>>>>>
>>>>>>>>> MPI_Type_struct in MPI-1 also used MPI_Aint.
>>>>>>>>>
>>>>>>>>> MPI_Type_create_indexed_block was added in MPI-2.1 (or 2.2?) and
>>>>>>>>> uses int.
>>>>>>>>>
>>>>>>>>> It all seems arbitrary to me.
>>>>>>>>>
>>>>>>>>> -- Pavan
>>>>>>>>>
>>>>>>>>> On 08/27/2011 05:18 AM, Jeff Squyres wrote:
>>>>>>>>>> An offhand guess: TYPE_CREATE_STRUCT was created in MPI-2,
>>>>>>>>>> whereas the rest were created in MPI-1.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Aug 27, 2011, at 3:54 AM, Pavan Balaji wrote:
>>>>>>>>>>
>>>>>>>>>>> Is there a reason why MPI_Type_create_struct was given the
>>>>>>>>>>> special privilege of using MPI_Aint to store displacements, while
>>>>>>>>>>> the remaining datatype creation routines use int? This would
>>>>>>>>>>> essentially disallow creation of a datatype as an offset to
>>>>>>>>>>> MPI_BOTTOM.
>>>>>>>>>>>
>>>>>>>>>>> -- Pavan
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> Pavan Balaji
>>>>>>>>>>> http://www.mcs.anl.gov/~balaji
>>>>>>>>>>> _______________________________________________
>>>>>>>>>>> mpi-forum mailing list
>>>>>>>>>>> mpi-forum at lists.mpi-forum.org
>>>>>>>>>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum
>>>>>>>>> --
>>>>>>>>> Pavan Balaji
>>>>>>>>> http://www.mcs.anl.gov/~balaji
>>>>>>>>> _______________________________________________
>>>>>>>>> mpi-forum mailing list
>>>>>>>>> mpi-forum at lists.mpi-forum.org
>>>>>>>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum
>>>>>>>> William Gropp
>>>>>>>> Director, Parallel Computing Institute
>>>>>>>> Deputy Director for Research
>>>>>>>> Institute for Advanced Computing Applications and Technologies
>>>>>>>> Paul and Cynthia Saylor Professor of Computer Science
>>>>>>>> University of Illinois Urbana-Champaign
>>>>>>>>
>>>>>>>>
>>>>>>>>
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