IsoEfficiency

IsoEfficiency - Performance of Parallel Systems The...

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1 Performance of Parallel Systems The execution time of a parallel program is influenced by many factors communication latency, idle times, load unbalance, synchronization overhead, … Measuring performance on parallel systems is not trivial simplest measure of performance such as wall-clock time is not adequate how does execution time changes when you change p ? CSE 721, Winter 2011 Iso-efficiency
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2 Performance of Parallel Systems Parallelism adds architectural dimensions to those that are crucial for performance traditional parameters: CPU speed, memory size, … new parameters: number of processors p, communication latency Basic questions on parallel program performance: – what kind of value can you expect for the run time T p ? – how good is T p with respect to the best serial run time T s Fundamental performance parameter is the speedup S = T s / T p
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Speedup Delicate points about speedup ( S ) – how do you get a fair measure of T s ? what if the best serial algorithm is not known/too slow? Theoretically, speedup can never exceed p speedup of p obtained if each processor runs for no more than T s / p Practically, one can see superlinear speedup possible reasons: nonoptimal serial algorithm, or
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IsoEfficiency - Performance of Parallel Systems The...

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