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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"><head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> <style type="text/css"> body { font-family: Verdana, Arial, Helvetica, sans-serif;} a.at-term { font-style: italic; } </style> <title>Multi-Level Parallel Programming Strategy</title> <meta name="Generator" content="ATutor"> <meta name="Keywords" content=""></head><body> <h3>Designing an MLP program:</h3>
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<li>Use message passing commands to initiate parallel processes, each of which will be responsible for the calculations required on separate sections of the global data. This technique is called domain decomposition or data decomposition. Another large-scale parallel processing
paradigm is the boss-worker approach or what is sometimes called task or functional decomposition. In this approach, one process (the boss) controls (through message passing) the operations of worker processes. The sample program
presented in this chapter uses both data and functional decomposition.</li>
<li>Each MPI process will hold its local data in its own
local memory. By doing this, the processor has faster access to most of the data it needs. In addition, duplication of data in many processor memories is avoided, thereby saving memory. When necessary, processes will transfer data to each other (i.e, between local memories) in the form of messages. This typically occurs with data at the boundaries of separate sections.</li>
<li>For the actual computations each MPI process does (which almost always involve loops of some kind) low-level parallel threads will be spawned. The threads will speed up the overall loop calculations by simultaneously executing the body of the loop but with different sets of iterations assigned to each thread. For <em>each </em> MPI process, threads are usually created with OpenMP directives. The MLP program shown in this chapter uses this technique.
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