Heavily depends on the application. Many applications running on a Top 10 system of the Top 500 are required to show good single threaded performance and good

Heavily depends on the application. Many applications running on a Top 10 system of the Top 500 are required to show good single threaded performance and good weak and strong scalings up to a big part of the system. Checking all these 3 check boxes is hard to do if your communication is not fully overlapped by computation. The smaller your problem, the better your single threaded performance (e.g. at some point your problem fits in L3), and the larger fraction of execution time that communication dominates. Even the poorest applications on these systems use non-blocking MPI to overlap communication with computation nowadays.