Hi,
I've committed a change allowing to configure the cache size and the related blocking size parameters at runtime. It use the trick that consists in storing runtime variables as static members of a global function. This way no need to have a shared binary lib just for that.
Here is the related "public" documented API:
/** \returns the currently set cpu cache size (in bytes) used to estimate the ideal blocking size parameters */
std::ptrdiff_t ei_cpuCacheSize();
/** Set the cpu cache size (in bytes) for blocking.
* This function also automatically set the blocking size parameters for each scalar type using the following formula:
* \code
* max_k = 4 * sqrt(cache_size/(64*sizeof(Scalar)));
* max_m = 2 * k;
* \endcode
* overwriting custom values set using the ei_setBlockingSizes function.
* \sa ei_setBlockingSizes */
void ei_setCpuCacheSize(std::ptrdiff_t cache_size);
/** Set the blocking size parameters \a maxK and \a maxM for the scalar type \a Scalar.
* Note that in practice there is no distinction between scalar types of same size.
* \sa ei_setCpuCacheSize */
template<typename Scalar>
void ei_setBlockingSizes(std::ptrdiff_t maxK, std::ptrdiff_t maxM);
/** \returns in \a makK, \a maxM the blocking size parameters for the scalar type \a Scalar.
* \sa ei_setBlockingSizes */
template<typename Scalar>
void ei_getBlockingSizes(std::ptrdiff_t& maxK, std::ptrdiff_t& maxM);
You can also see the complete diff there:
http://bitbucket.org/eigen/eigen/changeset/af6d26ce2778 to see how it is implemented in practice.
This API is just a proposal, if someone has better ideas...
gael