[mpiwg-rma] [EXTERNAL] Re: making dynamic windows suck less

[Barrett, Brian W]

The idea behind dynamic windows was to make them possible to implement today and push the vendors to support a more rational programming model tomorrow.  Like Jim, I'm not sure things are bleak enough that we should change.

In OFED, I think it would be very difficult today.  But with Mellanox's work to support dynamic registration cache in hardware, I think things are trending in the right direction there.

For Portals 4, if an implementation supports the BIND_INACCESSIBLE feature, and I think most implementations will, supporting dynamic windows is straight-forward.

PAMI and DMAPP are probably more difficult, but a firehose-like setup should be possible until hardware catches up.

Brian

--
  Brian W. Barrett
  Scalable System Software Group
  Sandia National Laboratories
________________________________
From: mpiwg-rma [mpiwg-rma-bounces at lists.mpi-forum.org] on behalf of Jeff Hammond [jeff.science at gmail.com]
Sent: Sunday, December 01, 2013 10:16 AM
To: MPI WG Remote Memory Access working group
Cc: MPI WG Remote Memory Access working group
Subject: [EXTERNAL] Re: [mpiwg-rma] making dynamic windows suck less

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<mailto: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<mailto: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<mailto:jeff.science at gmail.com>
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