Matrix diagonalization became slow after installing blas-openblas

I am using GNU Octave to diagonalize matrices. Installing openblas increases performance significantly.

I saw this news, installed blas-openblas and blas64-openblas, and updated.

After that, matrix diagonalization became much slower than before.

An workaround is to install, but it would be great if someone has some other suggestion. It takes a lot of time to compile openblas-lapack.

The following Octave code 12 seconds before the upgrade, and takes about 20 seconds afterwards. Installing openblas-lapack from AUR speeds it up once again.

ii = 1:2000;
a = sin(ii.^2 + ii');
a = (a + a')/2;