% mpicc -o pingpong -O pingpong.c
% mpirun -np 2 pingpong
Kind            n       time (sec)      Rate (MB/sec)
Send/Recv       1       0.000095        0.084078
Send/Recv       2       0.000095        0.168901
Send/Recv       4       0.000097        0.330131
Send/Recv       8       0.000132        0.484799
Send/Recv       16      0.000133        0.962880
Send/Recv       32      0.000145        1.770964
Send/Recv       64      0.000162        3.166782
Send/Recv       128     0.000195        5.245853
Send/Recv       256     0.000259        7.900853
Send/Recv       512     0.000352        11.623159
Send/Recv       1024    0.000566        14.484053
Send/Recv       2048    0.001055        15.530778
Send/Recv       4096    0.001642        19.952966
Send/Recv       8192    0.002680        24.456014
Send/Recv       16384   0.004773        27.462645
Send/Recv       32768   0.008801        29.786806
Send/Recv       65536   0.016895        31.032414
Send/Recv       131072  0.032911        31.860559
Send/Recv       262144  0.065010        32.258846
Send/Recv       524288  0.129104        32.487790
Send/Recv       1048576 0.258655        32.431620