Re: A Question about Dual CPU systems

[Chris Albertson <chrisalbertson90278@yahoo.com>]

Tom,

Under Linux and most other OSes, the operating system handles the
fact that there is/are N CPUs.  It keeps a list of tasks waiting
for the CPU.  These may be user tasks like your pipeline or Netscape
or they may be system takes like an FTP or Web Server.

The reason you might gain with a system that contains >1 CPUs is
if that list of tasks waiting a CPU is long. then the list gets worked
off faster.

You as a user can make that list longer by, say running multiple
copies of the pipeline at the same time, each in it's own xterm
window.

There is a utility called "top" that comes with Linux.  Run it and
it will show you CPU utilization and percent of idle time.  It
updates in real time.  Watch it as you use the system.  It should be
clear that if CPU utilization never goes near 100% adding a second
CPU would not help.  All it would do is move the utilization down to
below 50%

Computers can be bought with any number of CPUs installed, over 
100 if you want.  It's an economic question which is better, more
computers or more CPUs in the same computer.  With a network it
hardly matters.  Except for one point: When you buy two computers
you also get two disks, two VLB busses, two sets of RAM and so on
so you double more than just the CPU power.  Study that "top"
display to find you bottle neck, then address the bottle neck

In real life, with Intel CPUs the suite spot seems to be
1) Buy a faster CPU before you buy a second CPU.
2) More than two CPUs per box is not cost effective.  If you
need four CPUs buy two boxes.

Last week I went down to Boing's plant were they build Delta
rockets to look at their telemetry processing system.  What
did I see??  Six racks full of 2U tall, dual CPU PCs all
running Linux.  Something like 100 Dual CPU boxes.  What do
they do with it? Computational Fluid Dynamics.  They need
to compute the aerodynamic loads during a space launch.
The boxes are organized into a "cluster" and it operates much
like one large computer for tasks that are decomposable into
parallel processes.

In your case watch that "top" display.  Your goal is to peg
it at 100%.  


--- Tom Droege <tdroege2@earthlink.net> wrote:
> Now that I am running production on the data, I am thinking about how
> to 
> make the process go faster.  I am thinking about a dual cpu mother
> board.
> 
> I assume that such a system does not make the pipeline run faster. 
> Is this 
> true?  Seems to me that the code would have to know about the
> available cpu 
> and this would take a lot of special code.
> 
> I assume that what a second processor would buy me is the ability to 
> simultaneously work on the data while the pipeline was running at
> little 
> loss of power.  Is this true?
> 
> Does a dual cpu system make economic sense.  I.e. are they so
> expensive 
> that I would be better off running two computers and getting a
> network 
> going to move the data around?
> 
> Anyone have any recommended place to buy a dual cpu bare bones
> system?
> 
> Tom Droege
> 
> 


=====
Chris Albertson 
  Home:   310-376-1029  chrisalbertson90278@yahoo.com
  Cell:   310-990-7550
  Office: 310-336-5189  Christopher.J.Albertson@aero.org

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