[mpich-discuss] Error with MPI_Register_datarep

[Thakur, Rajeev]

To get file portability, most users use some higher-level library such as PnetCDF or HDF-5. Maybe you could write a small utility for the 32-bit users to do the data conversion before using the data.

> Maybe I can contribute? :)

Code contributions are always welcome :-). I will note that MPICH didn’t support the external32 file format for many years until Intel contributed code for it.

Rajeev


> On Mar 13, 2016, at 4:49 PM, Eric Chamberland <Eric.Chamberland at giref.ulaval.ca> wrote:
> 
> Le 2016-03-13 16:22, Thakur, Rajeev a écrit :
>> In the 19 years since the MPI-2 standard was released, you may be the first one requesting this functionality :-). I am curious what are you using it for?
> Here is the reason....
> 
> In 2012, when I read your book about MPI-2, I wrote all our I/O functions to use collective MPI I/O calls with "native" as datarep. I knew it would not be portable "as is" but the main usage is 64bits native format... then I told myself "It will be ok when I will want to read/write from 32 bits architectures or different endian style, since there is that user defined datarep possibility, as illustrated in chapet 9.1 of the book...", but unfortunately for me, I didn't _tested_ the functionality in 2012... :/
> 
> So we moved all our file formats (meshes, results, etc) to be aligned with the output of "native" datarep into a 64bits standard linux x86 architecture...  That means we have produced, for example, 1200 validations tests with input/output files into that format...
> 
> That is, of course, excluding all user data since 4 years..
> 
> No I am in the phase of porting the code to fully support 32bits architecture (we have an 32bit ubuntu running here, and working on windows port).
> 
> So, I did test for the first time the datarep functionality to be able to convert 64 bits "long int" from/to 32 bits "long int" for writing/reading in respect to existing file format...
> 
> It was all an easy task in my mind with the user datarep functionality just as it is in the standard..
> 
> But it appears I am the only one in the world (wow...) to request a way to have his files portable with MPI... without performance losses for the "main" usage which is 64bits...
> 
> Maybe there is another simple way to do this?
> 
> Anyway, I am now expecting that you will tell me it will never be implemented _just for me_... :/
> 
> Maybe I can contribute? :)
> 
> Thanks,
> 
> Eric
> 
>> 
>> Rajeev
>> 
>> 
>>> On Mar 13, 2016, at 1:51 PM, Eric Chamberland <Eric.Chamberland at giref.ulaval.ca> wrote:
>>> 
>>> Le 2016-03-10 18:04, Thakur, Rajeev a écrit :
>>>> Support for user-defined data representations has not been added to MPICH yet. There has not been much demand for it.
>>> Thanks for your answer...
>>> 
>>> Is it a "big" task?
>>> 
>>> Should it be scheduled so it may appear in a forthcoming version?
>>> 
>>> Thanks,
>>> 
>>> Eric
>>> 
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