To obtain the best performance with Intel MKL, ensure the following data alignment in your source code:
The routines with the names that contain the letters HP, OP, PP, SP, TP, UP in the matrix type and storage position (the second and third letters respectively) operate on the matrices in the packed format (see LAPACK "Routine Naming Conventions" sections in the Intel MKL Reference Manual). Their functionality is strictly equivalent to the functionality of the unpacked routines with the names containing the letters HE, OR, PO, SY, TR, UN in the same positions, but the performance is significantly lower.
If the memory restriction is not too tight, use an unpacked routine for better performance. In this case, you need to allocate N2/2 more memory than the memory required by a respective packed routine, where N is the problem size (the number of equations).
For example, to speed up solving a symmetric eigenproblem with an expert driver, use the unpacked routine:
call dsyevx(jobz, range, uplo, n, a, lda, vl, vu, il, iu, abstol, m, w, z, ldz, work, lwork, iwork, ifail, info)
where
a is the dimension
lda-by-n, which is at least
N2 elements,
instead of the packed routine:
call dspevx(jobz, range, uplo, n, ap, vl, vu, il, iu, abstol, m, w, z, ldz, work, iwork, ifail, info)
where ap is the dimension N*(N+1)/2.
Additional conditions can improve performance of the FFT functions.
The addresses of the first elements of arrays and the leading dimension values, in bytes (n*element_size), of two-dimensional arrays should be divisible by cache line size, which equals: