FFTW wisdom
===========

CP2K can write and read fftw3 wisdom files.  However, the default location is
"/etc/fftw/wisdom", which neither exists by default nor can it be written to by
regular users.  It is possible to set a location for the wisdom file in the
GLOBAL section of the CP2K input via the FFTW_WISDOM_FILE_NAME keyword, but this
is not well known.  Those wisdom files are not very large, in the 10s of
kilobyts.

So the Debian package could either write a wisdom file into the user's home
directory (~/.cp2k/wisdom or so),  or to a temporary directory like
/var/tmp/cp2k.  /var/lib/cp2k would probably not be a good choice again as it
might not be writable by the user.

On the other hand, some initial tests show that there is not a huge speedup to
gain here.

libsmm
======

This library can replace some BLAS routines with optimized code for small
matrix-matrix multiplications.  It can be optionally built from
tools/build_libsmm, but needs to be tuned to the machine and takes a while to
build as it brute-forces the best cache sizes etc. like ATLAS.

It also has to be included in the arch file for preprocessor defines
(-D__HAS_smm_dnn) and linkage (-lsmm_dnn).  We could build and integrate it in
case DEB_BUILD_OPTIONS includes "custom".  

autotune_grid
=============

Similar to libsmm, this builds a libgrid library tuned to the machine and to be
included via -D_HAVE_LIBGRID and libgrad.a.  Should also be built and
integrated in case DEB_BUILD_OPTIONS includes "custom".
