GROMACS

Check if there is any performance benefits to be had and in which regimes for x / f buffer opts without GPU update in:

• runs with DD and CPU update
  • x buffer ops: offloadable with a likely simple crossover heuristic threshold; i.e. below N atoms/core not offloaded (locals or also nonlocals, with/without CPU work?)
  • f buffer ops: heuristics likely more complex criteria (as it is combined with reductions)
• runs with / without DD and vsites
  • with GPU update requires D2H and H2D -- is it worth it, test use-cases (e.g. multiple ranks per GPU, both ensemble and DD runs, transfers might be overlapped)
  • without GPU update: same applies as above non-vistes runs just wait on D2H needs to be earlier