[Mpi-forum] Persistence Working Group Proposed
tony at cis.uab.edu
Wed Feb 25 12:17:55 CST 2009
Dick, there are plenty of one-end optimizations that are possible though.
The current technology is "half channels" and we want "whole channels" too.
Binding an actual channel (which I did propose in MPI-2) is also possible for further optimization, and I am open to that as well.
That makes a FIFO between sender and receiver, with single credit.
I agree that a channel is desirable also. We would make it part of the discussion. It is easy enough to specify...
----- Original Message -----
From: "Richard Treumann" <treumann at us.ibm.com>
To: "Main MPI Forum mailing list" <mpi-forum at lists.mpi-forum.org>
Sent: Wednesday, February 25, 2009 12:11:30 PM GMT -06:00 US/Canada Central
Subject: Re: [Mpi-forum] Persistence Working Group Proposed
In my opinion the lack of enthusiasm for point to point persistent operations does not tell us much about the usefulness of persistent operations in general. When the MPI-1 Forum decided an MPI_Isend_init or MPI_Irecv_init must be a local operation and that an MPI_Start of a persistent send on one side must match any form of receive (persistent or not) on the other (and vice versa) most of the opportunity for optimization was lost.
For a persistent collective to be fully optimized, the MPI library probably must be able to do collective communication at the CC_INIT and return to each task a persistent request handle that is irrevocably bound to all the handles created at the other tasks by this collective operation. It should not be valid to create two persistent BCAST requests at the root with different send buffers and one persistent BCAST at the non-roots just so root could BCAST from either buffer. (even if somebody thinks that would be a cool bit of generality)
Dick Treumann - MPI Team
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