[Mpi3-rma] [EXTERNAL] Re: Disp_unit in allocate_shared should be returned by win_shared_query?

[William Gropp]

The advice to users is not essential, and at this point, we should *only* be making essential changes.  This is a standards document, not a user manual.  I'm all for having man pages and tutorials say things like this, but we don't need it in the standard.

Bill

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



On Jul 26, 2012, at 4:22 PM, Rolf Rabenseifner wrote:

>> I guess we can add this advice nevertheless. I think this would also
>> cover Rolf's comment.
> 
> Not really. The text is orthogonal to my request.
> 
>>> Advice to users. If disp_unit values differ across processes in a
>>> shared memory window, the programmer may need to use the target's
>>> disp_unit value in address calculations and use different load/store
>>> operations depending on the target's disp_unit value. (End of advice
>>> to
>>> users.)
> 
> This is an advice especially for MPI_WIN_ALLOCATE_SHARED.
> It does not fit to MPI_WIN_ALLOCATE and the use of MPI_PUT/GET
> because in PUT/GET, the disp_unit works perfect.
> 
> My question was a general one at MPI_WIN_CREATE
> to tell the users that the major intend is that all disp_unit values 
> (related to the processes of one window handle)
> represent the extent of one common datatype.
> And, if one is doing different, this may cause a
> non-scaling memory overhead.
> 
> Rolf 
> 
> ----- Original Message -----
>> From: "Torsten Hoefler" <htor at illinois.edu>
>> To: "MPI 3.0 Remote Memory Access working group" <mpi3-rma at lists.mpi-forum.org>
>> Sent: Thursday, July 26, 2012 11:05:56 PM
>> Subject: Re: [Mpi3-rma] [EXTERNAL] Re: Disp_unit in allocate_shared should be returned by win_shared_query?
>> On Thu, Jul 26, 2012 at 11:18:05AM -0500, James Dinan wrote:
>>> I do have a concern that different disp_units can occur unexpectedly
>>> because of heterogeneous hardware or software -- e.g. MPMD launch
>>> with
>>> different executables or language incompatibility where both C and
>>> Fortran code are involved in creating the window.
>>> 
>>> Rather than ruling these cases out (option #1), how about including
>>> the
>>> following advice to users:
>>> 
>>> Advice to users. If disp_unit values differ across processes in a
>>> shared memory window, the programmer may need to use the target's
>>> disp_unit value in address calculations and use different load/store
>>> operations depending on the target's disp_unit value. (End of advice
>>> to
>>> users.)
>>> 
>>> If we included this, I think I would be ok with option #2.
>> I don't object, however, we're supposed to freeze the document by
>> today.
>> I guess we can add this advice nevertheless. I think this would also
>> cover Rolf's comment.
>> 
>>> An orthogonal observation -- it would have given us a lot more
>>> flexibility to define MPI_Win_shared_query as:
>>> 
>>> int MPI_Win_shared_get_attr(MPI_Win win, int target_rank, int
>>> win_keyval, void *attribute_val, int *flag)
>> Of course. I still like the MPI_Func(...) idea :-).
>> 
>> But I agree, this would also fit the current design with attributes
>> better. Hmm, is probably too late for such a syntactic sugar change.
>> Any
>> opinions?
>> 
>> All the Best,
>> Torsten
>> 
>> --
>> ### qreharg rug ebs fv crryF ------------- http://www.unixer.de/ -----
>> Torsten Hoefler | Performance Modeling and Simulation Lead
>> Blue Waters Directorate | University of Illinois (UIUC)
>> 1205 W Clark Street | Urbana, IL, 61801
>> NCSA Building | +01 (217) 244-7736
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> 
> -- 
> Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de
> High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
> University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
> Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
> Nobelstr. 19, D-70550 Stuttgart, Germany . (Office: Allmandring 30)
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