Subject: IO Anti-proposal

From: [email-masked] (James Cownie)
Date: Wed, 2 Sep 92 13:31:37 BST

IO Anti-proposal		
================

James Cownie 2 Sept 1992

When the HPFF established its working groups one of them was dedicated
to I/O extensions for parallel machines. The objective here was to 
define an expected set of extensions to standard Fortran (90) I/O
which could be expected on an MPP machine running HPF. 

However this group has been noticeably silent (a total of 12 messages
in 3 months, two of which were proposals, and one a note on the
silence of the group !), and quite a few of the messages actually
question whether we should do anything in this area. 

Marc Snir has now made a proposal on which NO comments appear to have
been received.  This proposal adds significant extensions to Fortran
I/O, and additional (non-standard) I/O functions.

So that we do not fall into the trap of voting this proposal in solely
on the grounds that it exists, I would like to make an "anti-proposal",
which is
      
       "HPF should contain NO I/O extensions"

Arguments for the Anti-proposal
-------------------------------

1) I/O systems on parallel machines are too architecturally different for
   there to be a useful abstraction on which the language model can build.

   Consider the difference between a machine with discs on each node,
   compared with one which has a high bandwidth disc system connected
   to the comms network, and thus globally accessible.

2) Fortran I/O is already highly expressive, (some people would say
   too expressive).

3) The HPF compiler must already know when it is performing I/O on distributed
   entities, and can therefore optimise their I/O to distributed files
   without any extensions to the source language.

4) The management of distributed files (and their implementation) is a
   matter for the operating system, not the language.

What this Anti-proposal does NOT say
------------------------------------

1) This proposal does NOT disallow any extensions which particular
   vendors may wish to make (indeed this would be impossible !), it
   simply says that there are no special I/O mechanisms mandated by HPF.

2) This proposal does NOT forbid the HPF run-time system from using
   whatever facilities the operating system provides for accessing
   "high performance" files, it merely says that the HPF language
   contains no I/O extensions. 

   [So the HPF system is entirely free to place a status='SCRATCH'
   file in the highest performance file system it likes, and
   distribute it as is appropriate for the machine, it is not up to
   the user to say all this however]

-- Jim
James Cownie 
Meiko Limited
650 Aztec West
Bristol BS12 4SD
England

Phone : +44 454 616171
FAX   : +44 454 618188
E-Mail: [email-masked] or [email-masked]

---

From: [email-masked]
Date: Fri, 4 Sep 92 01:02:02 CDT

Seconded.

Furthermore, are there any F90 I/O features that should
not be required in the initial HPF ?  (A question that
Marc Snir introduced 3 months ago..)

Peter