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cannam@127: <title>FFTW 3.3.5: FFTW MPI Performance Tips</title>
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cannam@127: <a name="FFTW-MPI-Performance-Tips"></a>
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cannam@127: Next: <a href="Combining-MPI-and-Threads.html#Combining-MPI-and-Threads" accesskey="n" rel="next">Combining MPI and Threads</a>, Previous: <a href="Avoiding-MPI-Deadlocks.html#Avoiding-MPI-Deadlocks" accesskey="p" rel="prev">Avoiding MPI Deadlocks</a>, Up: <a href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" accesskey="u" rel="up">Distributed-memory FFTW with MPI</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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cannam@127: <a name="FFTW-MPI-Performance-Tips-1"></a>
cannam@127: <h3 class="section">6.10 FFTW MPI Performance Tips</h3>
cannam@127:
cannam@127: <p>In this section, we collect a few tips on getting the best performance
cannam@127: out of FFTW’s MPI transforms.
cannam@127: </p>
cannam@127: <p>First, because of the 1d block distribution, FFTW’s parallelization is
cannam@127: currently limited by the size of the first dimension.
cannam@127: (Multidimensional block distributions may be supported by a future
cannam@127: version.) More generally, you should ideally arrange the dimensions so
cannam@127: that FFTW can divide them equally among the processes. See <a href="Load-balancing.html#Load-balancing">Load balancing</a>.
cannam@127: <a name="index-block-distribution-2"></a>
cannam@127: <a name="index-load-balancing-1"></a>
cannam@127: </p>
cannam@127:
cannam@127: <p>Second, if it is not too inconvenient, you should consider working
cannam@127: with transposed output for multidimensional plans, as this saves a
cannam@127: considerable amount of communications. See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>.
cannam@127: <a name="index-transpose-3"></a>
cannam@127: </p>
cannam@127:
cannam@127: <p>Third, the fastest choices are generally either an in-place transform
cannam@127: or an out-of-place transform with the <code>FFTW_DESTROY_INPUT</code> flag
cannam@127: (which allows the input array to be used as scratch space). In-place
cannam@127: is especially beneficial if the amount of data per process is large.
cannam@127: <a name="index-FFTW_005fDESTROY_005fINPUT-1"></a>
cannam@127: </p>
cannam@127:
cannam@127: <p>Fourth, if you have multiple arrays to transform at once, rather than
cannam@127: calling FFTW’s MPI transforms several times it usually seems to be
cannam@127: faster to interleave the data and use the advanced interface. (This
cannam@127: groups the communications together instead of requiring separate
cannam@127: messages for each transform.)
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