[mpiwg-rma] making dynamic windows suck less

[Pavan Balaji]

What you are suggesting is a valid improvement.  With the current MPI-3 standard dynamic windows are hard to implement efficiently on networks that require registration.

However, in the list of items to discuss that I had sent, I had a different proposal for the same problem.  The idea is to use an info hint where PUT/GETs and ATTACH/DETACHs are not interleaved.  This means that the MPI implementation will know that once I do a PUT to a location, it won’t be DETACHED and ATTACHED back again, thus potentially changing memory registration information.

With this info hint, the first PUT operation would be an active message that would fetch the registration information and the later PUT operations can use it.

  — Pavan

On Dec 1, 2013, at 11:16 AM, Jeff Hammond <jeff.science at gmail.com> wrote:

> How do you do pure (i.e. active-message and rendezvous-free) RDMA with just a virtual address (MPI_Aint) in (1) PAMI, (2) OFED, (3) DMAPP, (4) Portals4?
> 
> Jeff
> 
> Sent from my iPhone
> 
> On Dec 1, 2013, at 10:40 AM, Jim Dinan <james.dinan at gmail.com> wrote:
> 
>> Can the MPI_Win_memobj be an MPI_Aint?
>> 
>> I don't share this pessimism with respect to dynamic windows; I think we need to prove that these issues exist before we try to fix them.
>> 
>>  ~Jim.
>> 
>> 
>> On Wed, Nov 27, 2013 at 5:46 PM, Jeff Hammond <jeff.science at gmail.com> wrote:
>> Lots of people think - I take position on their correctness - that
>> dynamic windows are doomed to substandard performance.  I can
>> certainly see some potential for this on networks that require memory
>> registration.
>> 
>> Can we try to add an opaque object that can encapsulate memory
>> registration such that dynamic windows 2.0 would not have so many
>> problems?  If one were to send-recv not just the virtual address but
>> MPI_Win_memobj (to be named properly later), then maybe we could deal
>> with the shortcomings of IB, etc. w.r.t. RDMA and memory registration.
>> 
>> This is really just a thought.  I have no concrete proposal.  Maybe
>> people will have ideas in December.
>> 
>> Jeff
>> 
>> --
>> Jeff Hammond
>> jeff.science at gmail.com
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--
Pavan Balaji
http://www.mcs.anl.gov/~balaji