[mvapich-discuss] OSU Benchmark pt2pt bandwidth

[Tan Guangming]

The benchmark code in file "osu_bw.c" measure bandwidth by skipping
the first one/two communication operation and all commucations operate
on the same data and buffers. In fact, the first one acheive much
lower bandwidth. For example, we transfer 77MB messages, the first one
is only 1.1GB/s.
# OSU MPI Bandwidth Test v4.3
# Size      Bandwidth (MB/s)
loop 0: t = 0.067385 bw = 1151512533.291215
loop 1: t = 0.024156 bw = 3212217392.977516
loop 2: t = 0.024135 bw = 3215041557.475585
loop 3: t = 0.024151 bw = 3212915039.307534
loop 4: t = 0.024132 bw = 3215422723.669898
loop 5: t = 0.024151 bw = 3212883321.536630
loop 6: t = 0.024128 bw = 3215931085.875594
loop 7: t = 0.024154 bw = 3212502757.126178
loop 8: t = 0.024129 bw = 3215835755.718114
loop 9: t = 0.024153 bw = 3212629601.912008
loop 10: t = 0.024132 bw = 3215422723.669898
loop 11: t = 0.024154 bw = 3212502757.126178
loop 12: t = 0.024138 bw = 3214596977.783116
loop 13: t = 0.024156 bw = 3212249097.601548
loop 14: t = 0.024135 bw = 3215041557.475585
loop 15: t = 0.024125 bw = 3216344248.544254
loop 16: t = 0.024129 bw = 3215835755.718114
loop 17: t = 0.024154 bw = 3212471047.494779
loop 18: t = 0.024129 bw = 3215803980.254889
loop 19: t = 0.024152 bw = 3212788171.981205
loop 20: t = 0.024132 bw = 3215422723.669898
loop 21: t = 0.024151 bw = 3212915039.307534
77594624             3213.57

However, a real application doesn't match this commuication mode. In
general, every communication operates on different data (even differnt
buffer). Thus, is there any way to improve?