Archives

- Beowulf
- Beowulf Announce
- Scyld-users
- Beowulf on Debian

# [Beowulf] How does one calculate the scalability of one's code?

Many of your questions may have already been answered in earlier discussions or in the FAQ. The search results page will indicate current discussions as well as past list serves, articles, and papers.

Search

Chris Oubre chris_oubre at hotmail.com
Wed Jun 9 09:24:13 PDT 2004

```Hello,
My name is Chris Oubre.  I am a physics graduate student at Rice
University studying Maxwell's equations using a Finite Difference Time
Domain code.  I am trying to calculate the scalability of my code two ways

1) Fixed job size

For Fixed job size, I can use Amdahl's law S = N/ (b * N + (1-b)) and fit
the curve to find b ( the % of code that is serial)

Or I could use the Gustafson-Baris Law S = N - b(N - 1) and likewise fit to
find b

For fixed load size, I want to see how the algorithm behaves if I make the
jobs larger and increase the number of nodes to keep the job size constant.
Since I am using a 3D code, I double the job size and increase the number of
nodes by a factor of 8

I would expect that if the code scaled perfectly, they would execute in the
same amount of time.  I observe that the algorithm takes 1.6 times as long.
How do I report this?  What does this number tell me generally about the
scalability of my code?  Do I need to calculate something else?

To make the number more clear
Run1 Specs
Grid Size: 100 x 100 x 100
Nodes: 4
Time: 605 seconds

Run2 Specs
Grid Size: 200 x 200 x 200
Nodes: 32
Time: 944 seconds

So Run2 took ~ 1.6 times as long as Run1

Thank you for all of you help.

****************************************************
Christopher D. Oubre                               *
email: chris_oubre at hotmail.com                     *
research: http://cmt.rice.edu/~coubre              *
Web: http://www.angelfire.com/la2/oubre            *
Hangout: http://pub44.ezboard.com/bsouthterrebonne *
Phone:(713)348-2506  Fax:   (713)348-4150          *
Rice University                                    *
Department of Physics, M.S. 61                     *
6100 Main St.                       ^-^            *
Houston, Tx  77251-1892, USA       (O O)           *
-= Phlax=-                         ( v )           *
************************************m*m*************

```