  Many science advances have been possible thanks to the use of research
software, which has become essential to advancing virtually every Science,
Technology, Engineering and Mathematics (STEM) discipline and many non-STEM
disciplines including social sciences and humanities. And while much of it is
made available under open source licenses, work is needed to develop, support,
and sustain it, as underlying systems and software as well as user needs
evolve.
  In addition, the changing landscape of high-performance computing (HPC)
platforms, where performance and scaling advances are ever more reliant on
software and algorithm improvements as we hit hardware scaling barriers, is
causing renewed tension between sustainability of software and its performance.
We must do more to highlight the trade-off between performance and
sustainability, and to emphasize the need for sustainability given the fact
that complex software stacks don't survive without frequent maintenance; made
more difficult as a generation of developers of established and heavily-used
research software retire. Several HPC forums are doing this, and it has become
an active area of funding as well.
  In response, the authors organized and ran a panel at the SC18 conference.
The objectives of the panel were to highlight the importance of sustainability,
to illuminate the tension between pure performance and sustainability, and to
steer SC community discussion toward understanding and addressing this issue
and this tension. The outcome of the discussions, as presented in this paper,
can inform choices of advance compute and data infrastructures to positively
impact future research software and future research.
