  This paper describes a novel approach to neighbour-finding in Smoothed
Particle Hydrodynamics (SPH) simulations with large dynamic range in smoothing
length. This approach is based on hierarchical cell decompositions, sorted
interactions, and a task-based formulation. It is shown to be faster than
traditional tree-based codes, and to scale better than domain
decomposition-based approaches on shared-memory parallel architectures such as
multi-cores.
