Subject: static process creation

From: [email-masked]
Date: Fri, 5 Mar 93 10:00:25 PST

Tony Skjellum writes:

> Rik,
>
> Using the Delta's lack of an elegant process model to defend your
> point is not really valid.  They could have supported dynamic process
> creation, but just were too busy with other things, and did not see
> how useful the previously supported feature(s) were from iPSC960 and
> iPSC/1&2.

I was addressing the question of whether it is OK for MPI to
REQUIRE dynamic process creation, or whether it should include a
capability that requires only static processes.

My position is that a static process model should be supported.

I have no problem with MPI also providing a standard interface to
dynamic processes in environments where that can be done.  But I
strongly feel that a dynamic process interface should not be the only
one.

In the note that Tony refers to, I presented existence arguments that:

  a) The static process model can be supported cleanly on systems 
     that also support dynamic processes, such as workstation networks.
     (Someone else had asserted the contrary.)

  b) There exists at least one system (the Delta) that MPI seems to 
     target, and that does not support dynamic process creation.

This still seems like a valid argument for supporting static processes.

I agree that the argument would be stronger with a longer list of
systems that do not adequately support dynamic process creation.

I used the Delta because that's one example that I'm sure of.  I am
also sure that the iPSC/860 under NX does not have dynamic process
creation.  I believe that the iPSC/1 and /2 did have it, but I am not
so sure that their model/implementation allowed a process running on a
node to create a process on another node.  That capability seems to be
assumed by the arguments about why we want dynamic process creation.

If more examples are really needed, perhaps they can be provided by
people who have the facts.  I am not sure, as examples only, that the
CM-5, NCube-2, or Meiko systems provide all the dynamic process
support that's required.  I'd be pretty surprised if Intel was the
only vendor with current offerings that don't.

But my guess is that this is one of those issues where we have an
extended discussion and then all vote one way.  If we're going to
vote, then I propose that the issue be phrased

  "Should MPI support a static process model, 
   or should it support ONLY a dynamic process model?"

Is there actually debate on this issue?  Can anyone argue why a static
process model should NOT be supported?

--Rik Littlefield

---

From: L J Clarke <[email-masked]>
Date: Fri, 5 Mar 93 18:20:50 GMT

> only vendor with current offerings that don't.

FYI: Meiko Computing Surface - i.e., the machine they can deliver today
as opposed to the "new" machine - don't allow dynamic process creation. 
I believe that CM-5 only allows you to kick off an SPMD program, not
very dynamic really. 

Best Wishes
Lyndon

         /--------------------------------------------------------\
    e||) | Lyndon J Clarke    Edinburgh Parallel Computing Centre | e||) 
    c||c | Tel: 031 650 5021  Email: [email-masked]  | c||c 
         \--------------------------------------------------------/

---

From: [email-masked] (Al Geist)
Date: Fri, 5 Mar 93 17:45:31 -0500

Hi Rik,

Just a point of fact: we just got through testing a fully dynamic model
on the Intel i860. It is a part of the PVM 3.0 software.
Maybe the delta is the ONLY machine. Good thing only one was built.

I think your phrasing is ment to sway the reader to vote a particular way
(your way of course) We shouldn't loose track of the fact that
a static model is just a subset of the dynamic model.
There is no such thing as ONLY a dynamic model.

I can not argue that a static model should not be supported.
This is not the debate. The issue is should we limit MPI
to a static model (We haven't even voted to have process creation
of any kind yet) given that a more flexible model interface
already exists (PVM and others) 
but maybe a better argument is the ability to write more
fault tolerant applications with a dynamic model.

Al Geist

---

From: L J Clarke <[email-masked]>
Date: Sat, 6 Mar 93 18:57:01 GMT

I sent this yesterday, but it seems to have dissapaered into the great
bit bucket in the sky (nice phrase, Jim :-).

Best Wishes
Lyndon

---

From: L J Clarke <[email-masked]>
Date: Sat, 6 Mar 93 19:17:14 GMT

Hi Al, Rik, mpi-pt2pt world ...

I mailed out two other peices of kit which I understand don't allow
dynamic processes.  I should have pointed out, I guess, that to the best
of my knowledge this a restriction placed on the user by the "system"
software, and not by the hardware.  If my guess is correct The system
architects within the respective companies will have made a decision
that this would be the interface which they present to the user, and
they *could* have made a different decision.  So I hardly think that the
argument that there are existing systems which do not provide dynamic
process creation really is an argument that those systems should not be
asked to provide dynamic process creation within MPI, unless the vendors
among us advise that if MPI contains dynamic process creation they will
not implement that part of MPI for those systems *and* the existence of
such systems which do not implement MPI, or part thereof, will have a
significant affect on the market impact and penetration of MPI.  I'm
hardly a person who is able to say much of value on the last point. 

Best Wishes
Lyndon