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Parallel Setup

During setup, there are two input files to be read. One is a parameters file which is described in the previous section. Another is the target DC file. They are described in some detail in the previous section. For a large problem, the size of the DC file varies from several Mbytes to several tens of Mbytes. One may use the sequential setup for each node, where each node opens the DC file and reads the data independently. The argument for that is that the setup complexity is in the order of where is the maximum number of unknowns of the system. Since UNIX sets a limit on the number of files that can be open at any one time, for a coarse grain computer with a UNIX type of operating system this may easily exceed the limited number of files that can be opened at the same time. Also only one node can read data at a time so the rest of the nodes remain idle. This could be very time consuming. A solution is to use parallel I/O to achieve high performance. On the CM-5, CMMD provides a parallel I/O mode called global synchronous broadcast, in which a global file is accessed by all nodes simultaneously, with each node reading (or writing) the same data. This mode provides a significant increase in flexibility and parallelism for I/O operations.

For Intel and IBM machines, there is a global broadcasting mode in which one node opens the file and reads the data sequentially then broadcasts the data to the rest of nodes.


xshen@
Sat Dec 3 17:51:03 EST 1994