FEniCS uses MPI parallelization. An mpi run wll certainly use your cores, is it not using your memory well?
You can get indirect OpenMP support via your BLAS library. Make sure you have an optimized BLAS installed, that is built for openmp (or pthreads). There’s some BLAS discussion at Multicore and Ubuntu - #8 by dparsons or SLEPC solver running in Parallel - #2 by dparsons