  High Performance Computing (HPC) supercomputers are expected to play an
increasingly important role in HEP computing in the coming years. While HPC
resources are not necessarily the optimal fit for HEP workflows, computing time
at HPC centers on an opportunistic basis has already been available to the LHC
experiments for some time, and it is also possible that part of the pledged
computing resources will be offered as CPU time allocations at HPC centers in
the future. The integration of the experiment workflows to make the most
efficient use of HPC resources is therefore essential. This paper describes the
work that has been necessary to integrate LHCb workflows at a specific HPC
site, the Marconi-A2 system at CINECA in Italy, where LHCb benefited from a
joint PRACE (Partnership for Advanced Computing in Europe) allocation with the
other Large Hadron Collider (LHC) experiments. This has required addressing two
types of challenges: on the software application workloads, for optimising
their performance on a many-core hardware architecture that differs
significantly from those traditionally used in WLCG (Worldwide LHC Computing
Grid), by reducing memory footprint using a multi-process approach; and in the
distributed computing area, for submitting these workloads using more than one
logical processor per job, which had never been done yet in LHCb.
