  Use of standards-based workflows is still somewhat unusual by
high-performance computing users. In this paper we describe the experience of
using the Common Workflow Language (CWL) standards to describe the execution,
in parallel, of MPI-parallelised applications. In particular, we motivate and
describe the simple extension to the specification which was required, as well
as our implementation of this within the CWL reference runner. We discuss some
of the unexpected benefits, such as simple use of HPC-oriented performance
measurement tools, and CWL software requirements interfacing with HPC module
systems. We close with a request for comment from the community on how these
features could be adopted within versions of the CWL standards.
