[mpiwg-rma] Proposed Info Key

[Balaji, Pavan]

Sorry, I was clearly smoking something, so both my previous statements were incorrect:

1. Current mpich/master does check this unconditionally, but we are trying to make it conditional on an info key: alloc_shared.  The patch will be in soon.

2. Converting it to an AVL tree might not be as easy as I thought initially.  We do a bunch of Group_translate_ranks and Allgathers.  I’ll need to think more carefully to see if it’ll be possible to do this in an inexpensive way to avoid the info key altogether.

  — Pavan

On Oct 14, 2014, at 11:06 AM, Balaji, Pavan <balaji at anl.gov> wrote:

> 
> If we can optimize the search with an AVL tree, this info might be unnecessary.  It’d be cheap enough that we’d do it everytime anyway.
> 
>  — Pavan
> 
> On Oct 14, 2014, at 10:58 AM, Jeff Hammond <jeff.science at gmail.com> wrote:
> 
>> Thanks, Pavan, for sharing the details.  I forgot about the MPICH info
>> key used here.
>> 
>> Now that I understand the issue, I think we should pursue both
>> tickets, especially since my ticket is definitely 4.0 material.
>> Standardizing the info key that makes the MPICH solution portable in
>> the 3.1 timeframe is a good idea.
>> 
>> And I should note that this is not only an academic problem - there
>> are a number of projects making use of the (ppn+1)-windows trick
>> already and will benefit from the info key Mikhail proposed.
>> 
>> Jeff
>> 
>> On Tue, Oct 14, 2014 at 8:54 AM, Balaji, Pavan <balaji at anl.gov> wrote:
>>> 
>>> On Oct 14, 2014, at 10:43 AM, Jim Dinan <james.dinan at gmail.com> wrote:
>>>> IIUC, MPICH has started detecting this automatically without the info key, so this ticket may be moot.  Hopefully an MPICH developer familiar with this optimization can comment.
>>> 
>>> Yes, but we rely on an internal info key as well in order to avoid the search time.  Though I think we can optimize this search with an AVL tree or something.
>>> 
>>> Note that Jeff’s ticket gives more capability that this — it allows the user to do load/store accesses.  Your info key only allows the MPI implementation to internally optimize communication.
>>> 
>>> — Pavan
>>> 
>>> --
>>> Pavan Balaji  ✉️
>>> http://www.mcs.anl.gov/~balaji
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>> 
>> 
>> 
>> -- 
>> Jeff Hammond
>> jeff.science at gmail.com
>> http://jeffhammond.github.io/
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> 
> --
> Pavan Balaji  ✉️
> http://www.mcs.anl.gov/~balaji
> 
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--
Pavan Balaji  ✉️
http://www.mcs.anl.gov/~balaji