MPI-BCast - F2: Communication Lars Karlsson 2009-03-27...

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F2: Communication Lars Karlsson 2009-03-27
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Outline I Point-to-point I Broadcast I One-to-all (broadcast) I All-to-all I Reduction I All-to-one I All-to-all I Prefix sum (scan) I Personal communication I One-to-all (scatter) I All-to-all I Circular shift
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Point-to-point ( MPI Send / MPI Recv ) I An m -word message from one process to another takes time t s + t w m according to our basic communication cost model. I t s is the startup cost. I t w is the word transfer time or the inverse bandwidth . I We will assume cut-through routing and ignore the hop delay in the rest of this lecture. See the course literature for the details. I Typically, t s is in the microsecond range whereas t w is in the nanosecond range. I Beware that in all analyses the word size is implicit which means that you must be careful when you calculate t w from a bandwidth given in MB / s .
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MPI Bcast ) One process sends an m -word message to all other processes. Cost:
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MPI-BCast - F2: Communication Lars Karlsson 2009-03-27...

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