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(fftw.info)Caveats in Using Wisdom

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Caveats in Using Wisdom
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     For in much wisdom is much grief, and he that increaseth knowledge
     increaseth sorrow.  [Ecclesiastes 1:18]

   There are pitfalls to using `wisdom', in that it can negate FFTW's
ability to adapt to changing hardware and other conditions. For example,
it would be perfectly possible to export `wisdom' from a program
running on one processor and import it into a program running on another
processor.  Doing so, however, would mean that the second program would
use plans optimized for the first processor, instead of the one it is
running on.

   It should be safe to reuse `wisdom' as long as the hardware and
program binaries remain unchanged. (Actually, the optimal plan may
change even between runs of the same binary on identical hardware, due
to differences in the virtual memory environment, etcetera.  Users
seriously interested in performance should worry about this problem,
too.)  It is likely that, if the same `wisdom' is used for two
different program binaries, even running on the same machine, the plans
may be sub-optimal because of differing code alignments.  It is
therefore wise to recreate `wisdom' every time an application is
recompiled.  The more the underlying hardware and software changes
between the creation of `wisdom' and its use, the greater grows the
risk of sub-optimal plans.