  The combination of a non-overlapping Schwarz preconditioner and the Hybrid
Monte Carlo (HMC) algorithm is shown to yield an efficient simulation algorithm
for two-flavour lattice QCD with Wilson quarks. Extensive tests are performed,
on lattices of size up to 32x24x24x24, with lattice spacings a~0.08 fm and at
bare current-quark masses as low as 21 MeV.
