[mvapich-discuss] Re: loopback with mvapich2-1.2p1

[Dhabaleswar Panda]

> This env variable does not turn out into Loopback connections. I ran with
> the adapter which supports loopback connection as well.
> It makes non-loopback connections only.

How are you detecting that it is not working? Have you run OSU latency
test on your adapter with the shared memory variable being turned `on' and
`off'. You should see higher latency number when the loopback connection
is used (i.e., shared memory being `off').

Here are some sample numbers with and without shared memory.

When shared memory is on:

# OSU MPI Latency Test v3.1.1
# Size            Latency (us)
0                         0.79
1                         1.00
2                         0.99
4                         0.99
8                         0.99
16                        0.99
32                        1.01
64                        1.05
128                       1.14
256                       1.25
512                       1.39
1024                      1.63
2048                      1.83
4096                      2.48
8192                      3.86
16384                     7.08
32768                    13.79
65536                    27.05
131072                   44.38
262144                   77.17
524288                  137.95
1048576                 262.82
2097152                 499.93
4194304                1187.30

When shared memory is off:

# OSU MPI Latency Test v3.1.1
# Size            Latency (us)
0                         1.57
1                         1.52
2                         1.52
4                         1.52
8                         1.52
16                        1.52
32                        1.58
64                        1.76
128                       2.92
256                       3.23
512                       3.63
1024                      4.39
2048                      6.02
4096                      7.20
8192                      9.76
16384                    15.77
32768                    21.92
65536                    33.20
131072                   54.12
262144                   99.65
524288                  187.62
1048576                 367.76
2097152                 728.32
4194304                1557.02

DK