| Summary: | 碩士 === 國立中正大學 === 資訊工程研究所 === 89 === Network of workstation (NOW) is a cost-effective alternative to
massively parallel supercomputers. As commercially available
off-the-shelf processors become cheaper and faster, it is now
possible to build a PC or workstation cluster that provides high
computing power within a limited budget. However, a cluster may
consist of different types of processors and this heterogeneity
within a cluster complicates the design of efficient collective
communication protocols. This dissertation shows that a simple
heuristic called {fastest-node-first}
(FNF) is very effective in reducing broadcast
time for heterogeneous cluster systems. Despite the fact that FNF
heuristic fails to give the optimal broadcast time for a general
heterogeneous network of workstation, we prove that FNF always
gives the optimal broadcast time in several special cases of
clusters. Based on these special case results, we show that FNF
is an approximation algorithm that guarantees a competitive ratio
of 2. From these theoretical results we also derive techniques to
speed up the branch-and-bound search for the optimal broadcast
schedule in HNOW. Also we show that a simple algorithm called {
slowest-node-first} (SNF) is a very efficient reduction protocol
for heterogeneous clusters. First, we show that SNF is actually an
approximation algorithm with competitive ratio two. In addition,
we show that SNF does give the optimal reduction time when the
cluster consists of two types of processors, and the communication
speed ratio between them is at least two. Finally we apply these
theoretical results to branch-and-bound search and show that they
can reduce the search time by a factor of 500.
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