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110 Cray T3E User’s Guide

10.3 Scalability criteria at CSC

CSC imposes the following scalability criteria for Cray T3E applications:

The speed of the application has to increase by 50%, when

the number of processors is doubled.

For example, when doubling the processors from 8 to 16, the speed of

the code should be 1.5 times as much.

You can use Gustafson’s law for nice formulation of this criteria: com-

pute the same calculation using p and p/2 processors. Then you get the

relative speedup S

from Gustafson’s law:

= 2 − α

CSC’s criteria is S

> 1.5, which corresponds to the criteria

< 0.5

based on Gustafson’s law. This can be also formulated as follows:

In a large application, less than half of the time should be

used for sequential processing.

10.4 More information

See the manual pages for more information about timing, e.g., man

timex or man ICPUSED.

The basics of parallel programming are discussed in the textbook De-

signing and Building Parallel Programs [Fos95]. Another good textbook

is Introduction to Parallel Computing — Design and Analysis of Algo-

rithms [KGGK94].

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Cypress CSC-1200T Guia do Utilizador Página 110