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

Sun Jul 22 13:03:39 CDT 2012

I think this is a little strong.  This isn't necessary for the vast majority of MPI users; just for those at extreme scale.  A modification that restricted this to extreme scale might be acceptable.

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 22, 2012, at 12:28 PM, Rolf Rabenseifner wrote:

> On Wed, Jul 18, 2012 at 08:11:23PM +0000, Barrett, Brian W wrote:
>> I'm concerned with the change (and don't think it should happen 
>> at this point, as I want to be able to tell other people their 
>> changes are too big).  It's probably not another O(p) structure, 
>> since a process will have to know the other rank's disp_unit to 
>> do the memcpy during the communication operations, so we crossed 
>> the O(p) bridge when we added disp_unit to allocate_shared.
> 
> I would recommend to add two advices:
> 
>  Advice to users. For scalability reasons it is recommended
>  that all processes provide the same disp_unit argument
>  on all processes. End of advice to users.
> 
>  Advice to implementors. If the user provides the same
>  disp_unit argument on all processes of the communicator,
>  or a compressible list of values, it is necessary for 
>  scalability reasons to store this data as compact as possible.
>  End of advice to users.
> 
> Of course for all thre MPI_WIN_CREATE, MPI_WIN_AALOCATE, and
> MPI_WIN_ALLOCATE_SHARED.
> 
> Is this a good idea?
> If yes, can someone find a better wording for this proposal?
> 
> Best regards
> Rolf
> 
> ----- Original Message -----
>> From: "William Gropp" <wgropp at illinois.edu>
>> To: "MPI 3.0 Remote Memory Access working group" <mpi3-rma at lists.mpi-forum.org>
>> Sent: Sunday, July 22, 2012 7:12:27 PM
>> Subject: Re: [Mpi3-rma] [EXTERNAL] Re: Disp_unit in allocate_shared should be returned by win_shared_query?
>> What *exactly* are the proposals? I know in general, but some of the
>> statements make me wonder if I understand the proposal.
>> 
>> 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 22, 2012, at 10:55 AM, Torsten Hoefler wrote:
>> 
>>> Dear All,
>>> 
>>> I think we should discuss this more. Right now, we still have more
>>> votes
>>> in favor of this than against. The change is still committed and
>>> part of
>>> the "official release". The deadline is 7/26.
>>> 
>>> Please advise what to do!
>>> 
>>> Thanks,
>>> Torsten
>>> 
>>> On Wed, Jul 18, 2012 at 08:11:23PM +0000, Barrett, Brian W wrote:
>>>> I'm concerned with the change (and don't think it should happen at
>>>> this point, as I want to be able to tell other people their changes
>>>> are too big). It's probably not another O(p) structure, since a
>>>> process will have to know the other rank's disp_unit to do the
>>>> memcpy during the communication operations, so we crossed the O(p)
>>>> bridge when we added disp_unit to allocate_shared.
>>>> 
>>>> 
>>>> Brian
>>>> 
>>>> --
>>>> Brian W. Barrett
>>>> Scalable System Software Group
>>>> Sandia National Laboratories
>>>> ________________________________________
>>>> From: mpi3-rma-bounces at lists.mpi-forum.org
>>>> [mpi3-rma-bounces at lists.mpi-forum.org] on behalf of Jim Dinan
>>>> [dinan at mcs.anl.gov]
>>>> Sent: Wednesday, July 18, 2012 12:46 PM
>>>> To: mpi3-rma at lists.mpi-forum.org
>>>> Subject: [EXTERNAL] Re: [Mpi3-rma] Disp_unit in allocate_shared
>>>> should be returned by win_shared_query?
>>>> 
>>>> It's not inherently damaging, but it requires us to
>>>> maintain/provide
>>>> access to another O(p) structure and suggests to users that another
>>>> process' disp_unit is useful information, which is incorrect. IIRC,
>>>> we
>>>> did discuss this in the working group and intentionally omitted it.
>>>> 
>>>> ~Jim.
>>>> 
>>>> On 7/18/12 1:38 PM, Torsten Hoefler wrote:
>>>>> On Wed, Jul 18, 2012 at 01:18:53PM -0500, James Dinan wrote:
>>>>>> On 7/18/12 1:06 PM, Torsten Hoefler wrote:
>>>>>>> On Wed, Jul 18, 2012 at 01:08:43PM -0500, Pavan Balaji wrote:
>>>>>>>> 
>>>>>>>> On 07/18/2012 01:02 PM, Torsten Hoefler wrote:
>>>>>>>>> Jim,
>>>>>>>>>> Is one process' disp_unit meaningful at another process? I
>>>>>>>>>> thought that
>>>>>>>>>> this is not the case. MPI provides no other routines to query
>>>>>>>>>> another
>>>>>>>>>> process' disp_unit.
>>>>>>>>> It is something that the user is passing in. I don't know of a
>>>>>>>>> particular use-case but we can query all other arguments that
>>>>>>>>> each
>>>>>>>>> process passed. One more integer seemed safe to me.
>>>>>>>>> 
>>>>>>>>>> Also, what meaning does a disp_unit have in the context of
>>>>>>>>>> load/store
>>>>>>>>>> operations that will result from win_shared_query?
>>>>>>>>> Nothing.
>>>>>>>>> 
>>>>>>>>>> Maybe I'm missing something, but this doesn't seem necessary.
>>>>>>>>> Well, it's better to have it than to introduce it with a
>>>>>>>>> different name
>>>>>>>>> later. That was my main motivation. One could also use it in a
>>>>>>>>> library
>>>>>>>>> context to query. But that's weak, I know.
>>>>>>>> 
>>>>>>>> This doesn't seem critical, and can always be added in MPI-3.1
>>>>>>>> if we
>>>>>>>> find it necessary. No reason to rush it.
>>>>>>> 
>>>>>>> It cannot be added without a new function name. That was the
>>>>>>> concern
>>>>>>> here. Adding it seems less risk than not adding it. In addition,
>>>>>>> it is
>>>>>>> already added ;-).
>>>>>> 
>>>>>> I am concerned that this is a harmful change. The disp_unit from
>>>>>> one
>>>>>> process has no meaningful use at another process. If the user
>>>>>> wants to
>>>>>> know it for some reason, they can use a separate communication
>>>>>> operation.
>>>>> I believe the potential damage is very limited. But we can have a
>>>>> vote.
>>>>> 
>>>>> So far it's still yes: 5, no: 1
>>>>> 
>>>>> I'm just mediating, not making decisions.
>>>>> 
>>>>> Torsten
>>>>> 
>>>> 
>>>> _______________________________________________
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>>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
>>>> 
>>>> 
>>>> 
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>>>> 
>>> 
>>> --
>>> ### 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
>>> _______________________________________________
>>> mpi3-rma mailing list
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>> 
>> 
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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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