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author Chris Cannam
date Wed, 07 Sep 2016 10:40:32 +0100
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Chris@19 3 <title>FFTW MPI Performance Tips - FFTW 3.3.4</title>
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Chris@19 49 <a name="FFTW-MPI-Performance-Tips"></a>
Chris@19 50 <p>
Chris@19 51 Next:&nbsp;<a rel="next" accesskey="n" href="Combining-MPI-and-Threads.html#Combining-MPI-and-Threads">Combining MPI and Threads</a>,
Chris@19 52 Previous:&nbsp;<a rel="previous" accesskey="p" href="Avoiding-MPI-Deadlocks.html#Avoiding-MPI-Deadlocks">Avoiding MPI Deadlocks</a>,
Chris@19 53 Up:&nbsp;<a rel="up" accesskey="u" href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI">Distributed-memory FFTW with MPI</a>
Chris@19 54 <hr>
Chris@19 55 </div>
Chris@19 56
Chris@19 57 <h3 class="section">6.10 FFTW MPI Performance Tips</h3>
Chris@19 58
Chris@19 59 <p>In this section, we collect a few tips on getting the best performance
Chris@19 60 out of FFTW's MPI transforms.
Chris@19 61
Chris@19 62 <p>First, because of the 1d block distribution, FFTW's parallelization is
Chris@19 63 currently limited by the size of the first dimension.
Chris@19 64 (Multidimensional block distributions may be supported by a future
Chris@19 65 version.) More generally, you should ideally arrange the dimensions so
Chris@19 66 that FFTW can divide them equally among the processes. See <a href="Load-balancing.html#Load-balancing">Load balancing</a>.
Chris@19 67 <a name="index-block-distribution-426"></a><a name="index-load-balancing-427"></a>
Chris@19 68
Chris@19 69 <p>Second, if it is not too inconvenient, you should consider working
Chris@19 70 with transposed output for multidimensional plans, as this saves a
Chris@19 71 considerable amount of communications. See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>.
Chris@19 72 <a name="index-transpose-428"></a>
Chris@19 73
Chris@19 74 <p>Third, the fastest choices are generally either an in-place transform
Chris@19 75 or an out-of-place transform with the <code>FFTW_DESTROY_INPUT</code> flag
Chris@19 76 (which allows the input array to be used as scratch space). In-place
Chris@19 77 is especially beneficial if the amount of data per process is large.
Chris@19 78 <a name="index-FFTW_005fDESTROY_005fINPUT-429"></a>
Chris@19 79
Chris@19 80 <p>Fourth, if you have multiple arrays to transform at once, rather than
Chris@19 81 calling FFTW's MPI transforms several times it usually seems to be
Chris@19 82 faster to interleave the data and use the advanced interface. (This
Chris@19 83 groups the communications together instead of requiring separate
Chris@19 84 messages for each transform.)
Chris@19 85
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