From owner-sc22wg5@open-std.org Wed Nov 5 23:04:32 2008 Return-Path: X-Original-To: sc22wg5-dom7 Delivered-To: sc22wg5-dom7@www2.open-std.org Received: by www2.open-std.org (Postfix, from userid 521) id AB99ECA3428; Wed, 5 Nov 2008 23:04:32 +0100 (CET) X-Original-To: sc22wg5@open-std.org Delivered-To: sc22wg5@open-std.org Received: from mail.jpl.nasa.gov (sentrion2.jpl.nasa.gov [128.149.139.106]) by www2.open-std.org (Postfix) with ESMTP id 92402C178E7 for ; Wed, 5 Nov 2008 23:04:30 +0100 (CET) Received: from mprox1.jpl.nasa.gov (mprox1.jpl.nasa.gov [137.78.160.140]) by mail.jpl.nasa.gov (Switch-3.3.2mp/Switch-3.3.2mp) with ESMTP id mA5M4QKs018295 for ; Wed, 5 Nov 2008 22:04:27 GMT Received: from [137.79.7.57] (math.jpl.nasa.gov [137.79.7.57]) (authenticated bits=0) by mprox1.jpl.nasa.gov (Switch-3.2.6/Switch-3.2.6) with ESMTP id mA5M4Ohr015124 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT) for ; Wed, 5 Nov 2008 14:04:25 -0800 Subject: A comment on John Wallin's comments on Nick MacLaren's comments From: Van Snyder Reply-To: Van.Snyder@jpl.nasa.gov To: sc22wg5 In-Reply-To: References: Content-Type: text/plain Organization: Yes Date: Wed, 05 Nov 2008 14:04:24 -0800 Message-Id: <1225922664.26045.130.camel@math.jpl.nasa.gov> Mime-Version: 1.0 X-Mailer: Evolution 2.12.3 (2.12.3-8.el5_2.2) Content-Transfer-Encoding: 7bit X-Source-IP: math.jpl.nasa.gov [137.79.7.57] X-Source-Sender: Van.Snyder@jpl.nasa.gov X-AUTH: Authorized Sender: owner-sc22wg5@open-std.org Precedence: bulk This is a message I recently sent to the J3 list, re-sent to the WG5 list (with one small change). On Wed, 2008-11-05 at 12:15 -0800, John Wallin wrote: > Here is a simple example of an MPI coding horror. I have to pass a > Fortran derived type between nodes. > > Here is the code I need to use to even make this exchange possible. > Please note that a lot of code has been deleted so I don't overwhelm > everyone's email.[...] > > You might wonder what the 37 is the sphblock_counts. It is the number > of double precision numbers in a row within this particular data > structure. > > The important thing to note is that every time a grad student adds a > single element to the data structure, you have to alter the block > counts and sizes by hand. This leads to huge problems debugging and > maintaining the code if the base structures are modified. (And this > code is the best way I have found for doing it.) I remarked on this problem before m185, and proposed a trivial addition to the OPEN statement to allow message passing using I/O statements, which already know how to do DTIO and asynchronous, in 08-204. Subgroup didn't even consider it. If coarrays are kicked off the train in Tokyo, we really should go back and look at the directions proposed in 08-204 and 08-205. Fortran I/O applied to message passing should provide all the basic functionality of MPI, and would be far clearer. Within a single SMP, say a dual quad-core PC, one can already accomplish what's proposed in 08-204 with a pipe, but I haven't met a system yet where pipes work across NFS. 08-204 provides syntax for users to hook to stuff that vendors provide that go beyond NFS. 08-205 provides a way for users to roll their own, perhaps atop MPI, while hiding the ugly details behind I/O statements. -- Van Snyder | What fraction of Americans believe Van.Snyder@jpl.nasa.gov | Wrestling is real and NASA is fake? Any alleged opinions are my own and have not been approved or disapproved by JPL, CalTech, NASA, the President, or anybody else.