Wall-clock calculation times for different processes in the simulation with N_s = 64 000 and N_p = 64 000 (top pie chart) and N_s = 128 000 and N_p = 0 (bottom pie chart) in Fig. 1. The chart presents the wall-clock time for time intervals of the total simulation time (ten code units). Different numerical processes are indicated by colour: regular force calculations (blue), irregular force calculations (orange), adjustment processes (green), and others (red). It is immediately noticeable that the irregular force calculations consistently take less time overall in the simulation with massless particles.