Newsgroups: comp.parallel.mpi
From: Tom Impelluso <timpelluso@ucsd.edu>
Subject: MPI vs. shmem
Organization: UCSD SOE
Date: Mon, 30 Mar 1998 09:50:51 -0800
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Message-ID: <351FDB7B.41C67EA6@ucsd.edu>

hello!

Could I ask a question about mpi vs. shmem (which is the
native message passing on T3E/D?

OK, this is NOT meant to bait or start a war, I only wish
to play devil's advocate BRIEFLY, because I would like to
hear people's opinion on this...

I learned MPI and did some of my work in it.
I learned shmem and have done some work in it.

My area is Finite Element, so my work involves parallelizing
number crunchers...

I would like to state that it is better to code in that
native message passing, shmem, for this reason:

By learning shmem: 
1) My code runs faster than using MPI; 
2) I learned a great deal more about how the machine works;
3) I had quite a bit more fun;
4) Likely, it will be easier to learn other native message 
	passing from other libraries, because I spent the time
	with shmem.

The argument one could make is that MPI is a standard and shmem
is only for Cray.

However, I could respond that by taking time to learn shmem,
I gained an intuitive feel for message passing which could make
learning the native libraries for other architectures easier.


If I code well, it should not really take that much time to
port over, right?

And besides...
Basically, I want to do SIMPLE parallelization...
I am not sure if creating process groups is really necessary
(this could be the cause of my ignorance... maybe some people
are doing work with process groups, and that could be the place
where using just shmem could be a liability which MPI overcomes)

Continuing..

Yes, MPI is a standard (and, by the way, my argument will hold
for any "global" library, not just MPI), but eventually all standards
will pass on... Yes? no?  So, why not spend the time w/ the native
stuff.

Could people share their thoughts about this?
Again, this is not meant to bait or flame, so please do not be
hostile.


Thanks,
Tom