Newsgroups: comp.parallel.pvm
From: "Omar G. Stradella" <omar@boston.sgi.com>
Subject: Re: PVM on multi-processor SGI
Organization: Silicon Graphics, Inc.
Date: Thu, 11 Apr 1996 16:40:17 -0400
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Message-ID: <316D6E31.167E@boston.sgi.com>

Jeff Haferman wrote:
> 
> In article <316D11DE.41C67EA6@viewlogic.com>, Gary Greenstein <garyg@viewlogic.com> writes:
> > Jeff Haferman wrote:
> >>
> >> I have access to an SGI with 6 processors.  My PVM application
> >> actually only needs 4 of the processors.  How do I start up a
> >> pvmd on the individual processors on a single machine?
> >>
> >> Jeff
> >>
> >
> > You shouldn't have to do anything special.  We use SGIMP machines
> > with only one daemon for the machine, not one daemon per processor.
> > In the pvm console, just "add <name>" once.
> >
> 
> All right, I'll give it a try... but I am curious, on multiprocessor
> machines, if I just start up a single pvmd, and then spawn 4
> processes from my application, what kinds of values are returned
> by pvmconfig() for things like "host"?

pvmconfig will return only one "host" name entry (nhost=1).

> 
> Also, once I spawn my 4 tasks, suppose that they are split 2 and
> 2 over 2 processors due to system load.  Is this then a "static"
> configuration?  In other words, suppose a few moments after I spawn
> the tasks, the system load drops on all the processors on the machine.
> Then am I still stuck with the 2 processors that I got in the original
> spawn?

No, the scheduling is done dynamically by the OS. They tasks are not
"assigned" to any particular processor, they are run according to 
priority, availability of resources, etc as any other process. 
Processes tend to stick to some particular processor, at least for a
while (that's call processor affinity) to improve cache hit ratios.

Omar.

-- 
+-----------------------------------------------------------------------+
 Omar G. Stradella, Ph.D.                         Silicon Graphics, Inc. 
 One Cabot Road, Hudson, MA 01749            Supercomputing Applications
 E-mail: omar@boston.sgi.com                     Computational Chemistry 
 Phone:  +1-(508) 567-2258                    http://www.sgi.com/ChemBio 
 FAX:    +1-(508) 562-4755         http://reality.sgi.com/employees/omar 
+--------  Ph-nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn
---------+

