According to documentation (after some digging around the ebuild) : ( http://www.fftw.org/fftw2_doc/fftw_6.html ) ===================== --enable-threads Enables compilation and installation of the FFTW threads library (see Section Multi-threaded FFTW), which provides a simple interface to parallel transforms for SMP systems. (By default, the threads routines are not compiled.) ===================== It would be nice to have that documented in-ebuild, so users can see what this use flag actually does via euse/euses or similar tools. Right now it's a mystery as to what it exactly does.
