[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE: [mpi-21] ABI - call for working group
Hi,
How do morph layers find and load the right MPI library? How do they
manage variously sized opaque (and less opaque) objects? Are there any
performance penalties when those morph layers are used? Why did not they
become a de fact standard yet?
Best regards.
Alexander
--
Dr Alexander Supalov
Intel GmbH
Hermuelheimer Strasse 8a
50321 Bruehl, Germany
Phone: +49 2232 209034
Mobile: +49 173 511 8735
Fax: +49 2232 209029
-----Original Message-----
From: owner-mpi-21@xxxxxxxxxxxxx [mailto:owner-mpi-21@xxxxxxxxxxxxx] On
Behalf Of Greg Bronevetsky
Sent: Thursday, January 10, 2008 9:38 PM
To: mpi-21@xxxxxxxxxxxxx; mpi-21@xxxxxxxxxxxxx
Cc: mpi-21@xxxxxxxxxxxxx
Subject: Re: [mpi-21] ABI - call for working group
As far as I understand it, a morph layer such as MorphMPI or PnMPI is
a valid implementation of MPI from the point of any application. The
layer itself then chooses the local MPI implementation that it will
use to implement MPI functionality. As such, the application can come
pre-linked to its morph layer and the morph layer can do all the
platform-specific work without the need to recompile anything. While
I still see a need to standardize things like mpirun arguments, which
is something the user actually sees, most of the other use-cases for
the MPI ABI can be satisfied by open-source software that already
exists: MorphMPI and PnMPI.
It seems to me that a more feasible MPI ABI proposal would exclude
any features that solve problems that are already solved by the above
morph layers. Instead, it should focus on things that actually cannot
be done unless they're added to the standard. mpirun arguments is
one. What are the others?
Greg Bronevetsky
Post-Doctoral Researcher
1028 Building 451
Lawrence Livermore National Lab
(925) 424-5756
bronevetsky1@xxxxxxxx
At 10:35 AM 1/10/2008, William Yu wrote:
>Quite a detailed justification.
>
>I just curious why writing a "morph" layer is difficult because of
>the other libraries that use mpi is in use too?
>
>Does this mean because mathlab needs (example) parallel blas and
>both of them need mpi is causing the difficulty?
>
>I see linux device driver folk have the same issue but they seem to
>workaround it sufficiently well. Particularly those that involve
>both X and the linux kernel. (i worked on a capture card vendor in
>the past that distributed binary driver cores and open source
wrappers).
>
>Just curious because fixing an ABI obviously leaves less room for
>implementations.
>
>Thanks.
>
>________________ Reply Header ________________
>Subject: [mpi-21] ABI - call for working group
>Author: Edric Ellis <Edric.Ellis@xxxxxxxxxxxxxxx>
>Date: January 10th 2008 5:21 pm
>
>Hi All,
>
>This is a call for organisations to support a working group working
>towards defining an ABI for MPI. To make this happen, I need the
support
>of 3 other organisations.
>
>I realise that this is a large issue with many facets, many of which I
>don't understand fully (although I have tried to work through the
>various sources of information out there - the various mailing list
>discussions, and stuff like Greg Lindahl's paper). However, I hope that
>a working group would be able to develop a reasonable proposal. Below I
>include an outline from the perspective of The MathWorks as to what we
>would like to see:
>
>1. Motivation
>
>Many current users of MPI are perfectly happy to recompile their
>application to use different MPIs. However, a growing number of users
>are unable or unwilling to recompile an application to use a different
>MPI. Additionally, parallel processing is becoming increasingly
>important to software vendors since they can no longer rely on
>increasing single-core performance.
>
>Since it's the case I'm most familiar with, I will describe how MATLAB
>attempts to handle this sort of situation:
>1.1 An example application: MATLAB
>
>MATLAB is introducing explicit parallelism as our customers demand ever
>larger data sets and ever higher performance. One part of the value of
>our software is that we bring together various 3rd party libraries and
>put them into a convenient environment for scientists and engineers.
>Wherever possible, we prefer to allow our users to substitute their own
>favourite versions of BLAS, LAPACK etc.
>1.1.1 Why MATLAB can't currently use all MPIs
>
>Here are the main difficulties encountered when trying to make MATLAB
>work with the widest range of available MPI implementations:
>
>* We do not support customer recompilation of any part of MATLAB,
>therefore any library that we use must be binary compatible with the
one
>that we ship
>* We do support a "de facto" ABI defined by the implementation
>that we ship, several other MPIs match that one (but many don't).
>* Adding a "morph" layer is not simple, since we also build on
>many other libraries which use MPI (such as BLACS)
>* Our choice of "de facto" ABI is limited by the fact that we
only
>want to build and qualify one MPI across our 6 supported (commodity)
>platforms.
>* Aside: we provide means of dealing with the vagaries of
>differing mpirun/mpiexec schemes, and have a means of bypassing that
>altogether using MPI_Comm_connect/accept.
>
>1.1.2 What MATLAB expects to handle
>
>We fully expect to handle many of the issues relating to switching
>libraries:
>
>* we give a flexible means of specifying which binary to select
>
>* we attempt to avoid making assumptions about the details of the
>MPI implementation (i.e. we stick closely to the standard)
>
>2. Elements of a solution
>
>2.1 Scope
>
>Limit the scope to only those situations where it sensibly applies.
This
>may mean that it is not feasible to produce a solution for applications
>written in Fortran due to the following compiler issues:
>
>1. name mangling issues (MPI_INIT vs. mpi_init_ vs. ...)
>2. value of .TRUE.
>3. issues to do with calling convention
>
>2.2 mpi.h
>
>Define the contents of mpi.h more closely
>
>1. Define values of constants (such as MPI_COMM_WORLD etc.)
>2. Define size of MPI_Status
>3. Define size and types of MPI handles (such as MPI_Datatype
etc.)
>4. Define calling convention (e.g. cdecl vs. stdcall on WIN32
>platforms)
>
>2.3 Query implementation in use
>
>It may prove useful to provide a means of querying the MPI layer for a
>description of itself. For example, something along the lines of:
>
>int MPI_Version_info( char * buf, int bufSize )
>
>would allow an application to query at runtime the MPI implementation
>that it is using. The intention is that the output is for information
>only.
>
>3. Pros, Cons and Others
>
>3.1 Pros
>
>1. Allows application developers to ship binaries which can work
>with any MPI implementation
>
>2. MPI developers can test their implementation against those
>applications
>
>3. MPI implementors can benefit because of the potential expanded
>user base
>
>4. Implementations already have to support a translation layer for the
>Fortran interface, so there may not necessarily be a large
>implementation overhead (ref:
>http://www.open-mpi.org/community/lists/users/2005/03/0040.php)
>
>5. Hardware vendors can ensure that their hardware can be used
with
>the widest range of applications simply by ensuring that an ABI
>conforming MPI is available.
>
>3.2 Cons
>
>1. Standardizing types of MPI handles involves a significant
amount
>of work for MPI implementors (but see 3.1.4)
>
>2. Standardizing types of MPI handles may restrict MPI
>implementation choices.
>
>3. May not be able to resolve C++ / F90 name mangling issues
>
>3.3 Others
>
>1. Applications still must qualify against each MPI implementation
>that they wish to support.
>
>2. Naming of the shared library - applications may be reasonably
>expected to handle finding the right library using dlopen() or similar.
>
>Best regards,
>
>Edric.
>
>--
>Edric M. Ellis
>The MathWorks,
>Matrix House,
>Cambridge Business Park,
>Cambridge CB4 0HH, UK
>Tel: +44 (0)1223 226751
---------------------------------------------------------------------
Intel GmbH
Dornacher Strasse 1
85622 Feldkirchen/Muenchen Germany
Sitz der Gesellschaft: Feldkirchen bei Muenchen
Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer
Registergericht: Muenchen HRB 47456 Ust.-IdNr.
VAT Registration No.: DE129385895
Citibank Frankfurt (BLZ 502 109 00) 600119052
This e-mail and any attachments may contain confidential material for
the sole use of the intended recipient(s). Any review or distribution
by others is strictly prohibited. If you are not the intended
recipient, please contact the sender and delete all copies.