[Beowulf] Re: Xgrid and Mosix (fwd from prabhaka at apple.com)

Eugen Leitl eugen at leitl.org
Fri Dec 31 08:19:19 PST 2004

----- Forwarded message from Ernest Prabhakar <prabhaka at apple.com> -----

From: Ernest Prabhakar <prabhaka at apple.com>
Date: Thu, 30 Dec 2004 12:10:28 -0800
To: John Rudd <john at rudd.cc>
Cc: xgrid-users at lists.apple.com
Subject: Re: Xgrid and Mosix
X-Mailer: Apple Mail (2.688)

Hi John,

On Dec 29, 2004, at 7:37 PM, John Rudd wrote:
>So ... all of that leads up to: does anyone know if Xgrid is working  
>on this type of Application-Transparent Distributed Computing that  
>Mosix, OpenMosix, and I think OpenSSI have?

Thanks for your detailed comments, it was very educational.  While I  
can't comment on future plans, I do want to point out that Xgrid is  
really a "distributed resource manager" like Sun Grid Engine, not an  
'application environment' like MPI or OpenMP.   In particular, the  
Xgrid API and communication model are all designed around submitting  
and starting jobs -- they have absolutely no awareness of (or control  
over) what goes inside an application.

While I'm not directly familiar with Mosix et al, from your description  
it sounds like a kernel-level thread migration service, which is  
roughly analogous to the user-level task migration facilities of Xgrid.  
  From what I can tell, MOSIX also requires you to explicitly fork off  
separate serial threads or tasks, and doesn't provide any   
inter-process communication, so I'm not sure how it is really any  
different than Xgrid -- at least from the perspective of the  
*computation engine*.   Xgrid also allows you to take an existing,  
serializable application and run it (unmodified) on multiple systems.

The main difference, as best I can tell, is that MOSIX leverages the  
kernel's scheduler to automatically migrate discrete processes to other  
machines, whereas Xgrid requires explicit invocation (e.g., via the  
xgrid(1) command-line tool).

However, I'm no expert on these matters -- perhaps someone who  
understand both could comment more helpfully on a comparison between  
the two.

Ernie P.
Ernest N. Prabhakar, Ph.D. (408) 974-3075 <ernest at apple.com>
Xgrid Product Manager, System Software Marketing
Apple Computer; 303-4SW 3 Infinite Loop; Cupertino, CA 95014

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