% mpicc -o pingpong -O pingpong.c % mpirun -np 2 pingpong Kind n time (sec) Rate (MB/sec) Isend/Irecv 1 0.000102 0.078604 Isend/Irecv 2 0.000102 0.157401 Isend/Irecv 4 0.000103 0.310640 Isend/Irecv 8 0.000131 0.489217 Isend/Irecv 16 0.000131 0.974203 Isend/Irecv 32 0.000148 1.726855 Isend/Irecv 64 0.000165 3.100228 Isend/Irecv 128 0.000199 5.148454 Isend/Irecv 256 0.000258 7.942731 Isend/Irecv 512 0.000365 11.211941 Isend/Irecv 1024 0.000584 14.018996 Isend/Irecv 2048 0.001073 15.274495 Isend/Irecv 4096 0.001706 19.211164 Isend/Irecv 8192 0.002760 23.745680 Isend/Irecv 16384 0.004859 26.975654 Isend/Irecv 32768 0.008890 29.487223 Isend/Irecv 65536 0.016999 30.841831 Isend/Irecv 131072 0.033209 31.575328 Isend/Irecv 262144 0.065526 32.005061 Isend/Irecv 524288 0.130904 32.040958 Isend/Irecv 1048576 0.261332 32.099458