On BG/Q, the latency breakdown has similar components, but a significantly different behavior: MU Latency, the corresponding of HFI Latency on P7-IH, is lower (330 ns vs 430 ns). SPI Send, conversely, takes much more than the P7-IH equivalent (225 ns instead of 60 ns). The physical network on BG/Q shows a lower latency: 40 ns on the links and 40 ns on the router. Finally, SPI Receive takes 125 ns which is slightly lower than on P7-IH. Sum-ming all of these together, we have a latency of 760 ns for BG/Q and 900 ns for P7-IH. These numbers confirm the latency results of our runtime, with BG/Q faster (in terms of latency) with respect to P7-IH. The difference on MPI_Send is all given by the MPI runtime, that is much faster on P7-IH (300 ns) than on BG/Q (1070 ns).