Another Performance Measure

Work = (number of processors) x (running time)

ListRank: Work =

A PRAM algorithm A is work-efficient with respect to another algorithm B if Work(A) = .

Usually B is the best serial algorithm.

ListRank:

Serial:

Work = $\Theta(n)$ (one processor needs n time)

PRAM:

Work = $\Theta(n \lg n)$
Is the ListRank algorithm work efficient? No

Efficiency:

Speedup / #Processors.
An algorithm is thus work-efficient if Efficiency = $\Theta(1)$.