High Performance Block Incomplete LU Factorization

Abstract: Many application problems that lead to solving linear systems make use of preconditioned Krylov subspace solvers to compute their solution. Among the most popular preconditioning approaches are incomplete factorization methods either as single-level approaches or within a multilevel framework. We will present a block incomplete factorization that is based on skillfully blocking the system initially and throughout the factorization. This approach allows for the use of cache-optimized dense matrix kernels such as level-3 BLAS or LAPACK. We will demonstrate how this block approach outperforms the scalar method often by orders of magnitude on modern architectures, paving the way for its prospective use inside various multilevel incomplete factorization approaches or other applications where the core part relies on an incomplete factorization.