Basic HTML version of Foils prepared April 22 2000

Foil 28 Performance of Simplest Parallel DIT FFT IV

From Parallel FFT and use in PDE Solvers Computational Science Class CPS615 -- Winter Semester 2000. by Geoffrey C. Fox
1 One can however for DIT (and DIF) get much better performance if one avoids the "owner computes rule" and changes the processor which calculates a given FFT component.
2 This can seen by examining a typical step in a phase of parallel FFT where communication is needed in current algorithm. Consider any two processors -- called a and b --- which need to swap data in current algorithm
  • a has vector fa and b has a vector fb -- both of length N/Nproc
  • Currently we swap N/Nproc numbers by sending fb to a and fa to b
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