Subject: Some notes on the January MPI workshop in Europe

From: Rusty Lusk <[email-masked]>
Date: Wed, 26 Jan 1994 13:48:31 -0600

This is not a complete set of minutes of the January meeting, but it describes
immediate responses to the presentations of those in the European parallel
computing community who came to the workshop and told us of their impressions
of MPI and how it would or would not meet their needs.  

(Rolf, can you get this into the hands of as many attendees as is convenient?)

Rusty Lusk

___________________________________________________________________________

Notes on how we decided to respond to the user "requests" at the January
meeting.   This note represents the thoughts of the 12 committee
memeber present at the European meeting.  They will be presented to
the whole committee for a formal vote at the meeting in Knoxville.

Buffering
---------

The users were clearly terrified by the discussion of "safety" into thinking
that we were mandating that there be no buffering.  We decided to change the
wording in the draft to make it clear that MPI implementations were intended
to support buffering.  We decided to consider whether user-specifies-buffer
should be mandatory.

Error Codes
----- -----

They noticed, correctly, that without at least some list of error codes, it
would be difficult to write portable programs that checked for errors.  Rusty
Lusk volunteered to collect some error codes and propose them at the Knoxville
meeting.  Paul Pierce suggested that there be a way of combining detailed
error codes into "error classes".  Perhaps MPI could at least specify the
error classes.  We will discuss this at the next meeting.

Timers
------

The users asked for some kind of portable timer routine.  We decided to find
out what the POSIX clock routines were and then mandate that some of them be
part of any MPI implementation.  Bob Knighten will send us the specs for the
POSIX clock routines.

Tags
----

The users asked for some guaranteed tag range, for portability.  We decided
to specify that the tag lower bound is at most 0 and there is a contiguous
range available, up to X, where X is greater than or equal to 256.  (We may
have changed this to 128 later.)  An implementation note will be added to the
draft to state that 256 (128) was chosen since it could allow for a
lightweight message header but implementors on most MPP systems should
consider this a minimum that should be exceeded.  There will be an
environmental enquiry function to give the actual value of X and the lower
bound..

Validation Suite
---------- -----

ANL and ORNL will collaborate on a publicly available set of MPI programs, but
we as yet have no plans for a rigorous validation suite.

MPI Forum Followup
--- ----- --------

David Walker will organize mailing lists managed by current chapter authors to
allow comments to continue to be received forever.  A committee will continue
to exist for the forseeable future to provide interpretation of the standard
when questions arise.

Partial Receive
------- -------

The users asked for a way to unpack a message incrementally, as in PVM.  We
decided to keep thinking about this.  (It was later in the meeting when some
of us came up with a plan for a MPI_PACK and MPI_UNPACK that would meet this
requirement;  it will be proposed on the net soon and discussed at the
Knoxville meeting.)

Parameterized Datatypes
------------- ---------

We decided to defer this topic to the Fortran-90 binding discussion, whenever
that occurs. 

Remote Copy
------ ----

We decided to stick to our original position that remote copy was outside the
scope of the MPI goal.  It is anticipated that this would be a topic to be
included in MPI-2 discussions.