One more thing to add, this is 100% reproducible when running with srun and no 
output when running with mpirun:

Mpiexec
[adm_forai@login-01 ~]$ srun -N 2 -n 2 --pty bash
[adm_forai@cn-21 ~]$ mpiexec -np 2 IMB-MPI1 PingPong
libibverbs: Warning: no node_type attr under /sys/class/infiniband/usnic_0.
libibverbs: Warning: no node_type attr under /sys/class/infiniband/usnic_0.
libibverbs: Warning: no node_type attr under /sys/class/infiniband/usnic_0.
 benchmarks to run PingPong
#------------------------------------------------------------
#    Intel (R) MPI Benchmarks 4.1, MPI-1 part
#------------------------------------------------------------
# Date                  : Mon Nov 13 14:28:57 2017
# Machine               : x86_64
# System                : Linux
# Release               : 3.10.0-514.2.2.el7.x86_64
# Version               : #1 SMP Tue Dec 6 23:06:41 UTC 2016
# MPI Version           : 3.1
# MPI Thread Environment:

# New default behavior from Version 3.2 on:

# the number of iterations per message size is cut down
# dynamically when a certain run time (per message size sample)
# is expected to be exceeded. Time limit is defined by variable
# "SECS_PER_SAMPLE" (=> IMB_settings.h)
# or through the flag => -time



# Calling sequence was:

# IMB-MPI1 PingPong

# Minimum message length in bytes:   0
# Maximum message length in bytes:   4194304
#
# MPI_Datatype                   :   MPI_BYTE
# MPI_Datatype for reductions    :   MPI_FLOAT
# MPI_Op                         :   MPI_SUM
#
#

# List of Benchmarks to run:

# PingPong

#---------------------------------------------------
# Benchmarking PingPong
# #processes = 2
#---------------------------------------------------
       #bytes #repetitions      t[usec]   Mbytes/sec
            0         1000        11.22         0.00
            1         1000        11.26         0.08
            2         1000        11.18         0.17
            4         1000        11.16         0.34
            8         1000        11.19         0.68
           16         1000        11.18         1.36
           32         1000        11.28         2.71
           64         1000        11.40         5.35
          128         1000        11.62        10.51
          256         1000        12.08        20.20
          512         1000        12.75        38.30
         1024         1000        14.44        67.61
         2048         1000        16.00       122.04
         4096         1000        19.19       203.54
         8192         1000        25.41       307.42
        16384         1000        30.88       506.04
        32768         1000        38.29       816.18
        65536          640        56.42      1107.79
       131072          320        87.01      1436.58
       262144          160       162.14      1541.92
       524288           80       257.73      1940.02
      1048576           40       450.37      2220.39
      2097152           20       806.20      2480.79
      4194304           10      1776.69      2251.38


# All processes entering MPI_Finalize

[adm_forai@cn-21 ~]$


SRUN


[adm_forai@login-01 ~]$ srun -N 2 -n 2 IMB-MPI1 PingPong
libibverbs: Warning: no node_type attr under /sys/class/infiniband/usnic_0.
libibverbs: Warning: no node_type attr under /sys/class/infiniband/usnic_0.
 benchmarks to run PingPong
#------------------------------------------------------------
#    Intel (R) MPI Benchmarks 4.1, MPI-1 part
#------------------------------------------------------------
# Date                  : Mon Nov 13 14:27:26 2017
# Machine               : x86_64
# System                : Linux
# Release               : 3.10.0-514.2.2.el7.x86_64
# Version               : #1 SMP Tue Dec 6 23:06:41 UTC 2016
# MPI Version           : 3.1
# MPI Thread Environment:

# New default behavior from Version 3.2 on:

# the number of iterations per message size is cut down
# dynamically when a certain run time (per message size sample)
# is expected to be exceeded. Time limit is defined by variable
# "SECS_PER_SAMPLE" (=> IMB_settings.h)
# or through the flag => -time



# Calling sequence was:

# /software/171020/software/imb/4.1-foss-2017a/bin/IMB-MPI1 PingPong

# Minimum message length in bytes:   0
# Maximum message length in bytes:   4194304
#
# MPI_Datatype                   :   MPI_BYTE
# MPI_Datatype for reductions    :   MPI_FLOAT
# MPI_Op                         :   MPI_SUM
#
#

# List of Benchmarks to run:

# PingPong

#---------------------------------------------------
# Benchmarking PingPong
# #processes = 2
#---------------------------------------------------
       #bytes #repetitions      t[usec]   Mbytes/sec
            0         1000        11.73         0.00
            1         1000        11.83         0.08
            2         1000        11.66         0.16
            4         1000        11.64         0.33
            8         1000        11.70         0.65
           16         1000        11.73         1.30
           32         1000        11.81         2.58
           64         1000        12.01         5.08
          128         1000        12.23         9.98
          256         1000        12.63        19.33
          512         1000        13.35        36.58
         1024         1000        14.98        65.18
         2048         1000        16.43       118.85
         4096         1000        19.69       198.38
         8192         1000        26.38       296.18
[cn-21:18790] unrecognized payload type 255
[cn-21:18790] base = 0xa0c840, proto = 0xa0c840, hdr = 0xa0c880
[cn-21:18790]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   10: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   20: da 89 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-21:18790]   30: 0a 95 00 20 0a 95 00 1f a3 1a e3 8c 00 28 9c 10
[cn-21:18790]   40: 01 00 00 00 00 00 8b d0 00 00 8d 8f 00 00 00 00
[cn-21:18790]   50: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790] unrecognized payload type 255
[cn-21:18790] base = 0xa0c500, proto = 0xa0c500, hdr = 0xa0c540
[cn-21:18790]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   10: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   20: da 89 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-21:18790]   30: 0a 95 00 20 0a 95 00 1f a3 1a e3 8c 00 28 9b 10
[cn-21:18790]   40: 01 00 00 00 00 00 8b d0 00 00 8e 8f 00 00 00 00
[cn-21:18790]   50: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790] unrecognized payload type 255
[cn-21:18790] base = 0xa0c1c0, proto = 0xa0c1c0, hdr = 0xa0c200
[cn-21:18790]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   10: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   20: da 89 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-21:18790]   30: 0a 95 00 20 0a 95 00 1f a3 1a e3 8c 00 28 9a 10
[cn-21:18790]   40: 01 00 00 00 00 00 8b d0 00 00 8f 8f 00 00 00 00
[cn-21:18790]   50: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790] unrecognized payload type 255
[cn-21:18790] base = 0xa0be80, proto = 0xa0be80, hdr = 0xa0bec0
[cn-21:18790]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   10: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   20: da 89 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-21:18790]   30: 0a 95 00 20 0a 95 00 1f a3 1a e3 8c 00 28 99 10
[cn-21:18790]   40: 01 00 00 00 00 00 8b d0 00 00 90 8f 00 00 00 00
[cn-21:18790]   50: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790] unrecognized payload type 255
[cn-21:18790] base = 0xa0bb40, proto = 0xa0bb40, hdr = 0xa0bb80
[cn-21:18790]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   10: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   20: da 89 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-21:18790]   30: 0a 95 00 20 0a 95 00 1f a3 1a e3 8c 00 28 98 10
[cn-21:18790]   40: 01 00 00 00 00 00 8b d0 00 00 91 8f 00 00 00 00
[cn-21:18790]   50: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790] unrecognized payload type 255
[cn-21:18790] base = 0xa0b800, proto = 0xa0b800, hdr = 0xa0b840
[cn-21:18790]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   10: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   20: da 89 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-21:18790]   30: 0a 95 00 20 0a 95 00 1f a3 1a e3 8c 00 28 97 10
[cn-21:18790]   40: 01 00 00 00 00 00 8b d0 00 00 92 8f 00 00 00 00
[cn-21:18790]   50: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790] unrecognized payload type 255
[cn-21:18790] base = 0xa0b4c0, proto = 0xa0b4c0, hdr = 0xa0b500
[cn-21:18790]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   10: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   20: da 89 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-21:18790]   30: 0a 95 00 20 0a 95 00 1f a3 1a e3 8c 00 28 96 10
[cn-21:18790]   40: 01 00 00 00 00 00 8b d0 00 00 93 8f 00 00 00 00
[cn-21:18790]   50: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790] unrecognized payload type 255
[cn-21:18790] base = 0xa0b180, proto = 0xa0b180, hdr = 0xa0b1c0
[cn-21:18790]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   10: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   20: da 89 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-21:18790]   30: 0a 95 00 20 0a 95 00 1f a3 1a e3 8c 00 28 95 10
[cn-21:18790]   40: 01 00 00 00 00 00 8b d0 00 00 94 8f 00 00 00 00
[cn-21:18790]   50: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790] unrecognized payload type 255
[cn-21:18790] base = 0xa0ae40, proto = 0xa0ae40, hdr = 0xa0ae80
[cn-21:18790]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   10: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   20: da 89 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-21:18790]   30: 0a 95 00 20 0a 95 00 1f a3 1a e3 8c 00 28 94 10
[cn-21:18790]   40: 01 00 00 00 00 00 8b d0 00 00 95 8f 00 00 00 00
[cn-21:18790]   50: 00 00 00 00 00 00 06 02 ff 0c a2 ff 06 02 ff 0c
[cn-21:18790]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-21:18790]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990] unrecognized payload type 255
[cn-22:15990] base = 0xa11880, proto = 0xa11880, hdr = 0xa118c0
[cn-22:15990]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   10: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   20: a2 ff 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-22:15990]   30: 0a 95 00 1f 0a 95 00 20 e3 8c a3 1a 00 28 f8 01
[cn-22:15990]   40: 00 00 00 00 00 00 8b d0 00 00 fb 13 00 00 00 00
[cn-22:15990]   50: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990] unrecognized payload type 255
[cn-22:15990] base = 0xa11540, proto = 0xa11540, hdr = 0xa11580
[cn-22:15990]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   10: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   20: a2 ff 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-22:15990]   30: 0a 95 00 1f 0a 95 00 20 e3 8c a3 1a 00 28 f6 01
[cn-22:15990]   40: 00 00 00 00 00 00 8b d0 00 00 fd 13 00 00 00 00
[cn-22:15990]   50: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990] unrecognized payload type 255
[cn-22:15990] base = 0xa11200, proto = 0xa11200, hdr = 0xa11240
[cn-22:15990]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   10: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   20: a2 ff 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-22:15990]   30: 0a 95 00 1f 0a 95 00 20 e3 8c a3 1a 00 28 f4 01
[cn-22:15990]   40: 00 00 00 00 00 00 8b d0 00 00 ff 13 00 00 00 00
[cn-22:15990]   50: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990] unrecognized payload type 255
[cn-22:15990] base = 0xa10ec0, proto = 0xa10ec0, hdr = 0xa10f00
[cn-22:15990]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   10: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   20: a2 ff 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-22:15990]   30: 0a 95 00 1f 0a 95 00 20 e3 8c a3 1a 00 28 f3 01
[cn-22:15990]   40: 00 00 00 00 00 00 8b d0 00 00 00 14 00 00 00 00
[cn-22:15990]   50: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990] unrecognized payload type 255
[cn-22:15990] base = 0xa10b80, proto = 0xa10b80, hdr = 0xa10bc0
[cn-22:15990]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   10: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   20: a2 ff 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-22:15990]   30: 0a 95 00 1f 0a 95 00 20 e3 8c a3 1a 00 28 f2 01
[cn-22:15990]   40: 00 00 00 00 00 00 8b d0 00 00 01 14 00 00 00 00
[cn-22:15990]   50: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990] unrecognized payload type 255
[cn-22:15990] base = 0xa10840, proto = 0xa10840, hdr = 0xa10880
[cn-22:15990]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   10: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   20: a2 ff 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-22:15990]   30: 0a 95 00 1f 0a 95 00 20 e3 8c a3 1a 00 28 f0 01
[cn-22:15990]   40: 00 00 00 00 00 00 8b d0 00 00 03 14 00 00 00 00
[cn-22:15990]   50: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990] unrecognized payload type 255
[cn-22:15990] base = 0xa10500, proto = 0xa10500, hdr = 0xa10540
[cn-22:15990]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   10: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   20: a2 ff 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-22:15990]   30: 0a 95 00 1f 0a 95 00 20 e3 8c a3 1a 00 28 ee 01
[cn-22:15990]   40: 00 00 00 00 00 00 8b d0 00 00 05 14 00 00 00 00
[cn-22:15990]   50: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990] unrecognized payload type 255
[cn-22:15990] base = 0xa101c0, proto = 0xa101c0, hdr = 0xa10200
[cn-22:15990]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   10: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   20: a2 ff 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-22:15990]   30: 0a 95 00 1f 0a 95 00 20 e3 8c a3 1a 00 28 ec 01
[cn-22:15990]   40: 00 00 00 00 00 00 8b d0 00 00 07 14 00 00 00 00
[cn-22:15990]   50: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990] unrecognized payload type 255
[cn-22:15990] base = 0xa0fe80, proto = 0xa0fe80, hdr = 0xa0fec0
[cn-22:15990]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   10: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   20: a2 ff 08 00 45 00 00 3c 00 00 40 00 08 11 5d 49
[cn-22:15990]   30: 0a 95 00 1f 0a 95 00 20 e3 8c a3 1a 00 28 eb 01
[cn-22:15990]   40: 00 00 00 00 00 00 8b d0 00 00 08 14 00 00 00 00
[cn-22:15990]   50: 00 00 00 00 00 00 06 02 ff 0c da 89 06 02 ff 0c
[cn-22:15990]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[cn-22:15990]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
        16384         1000        32.29       483.84
        32768         1000        41.42       754.43
        65536          640        57.21      1092.55
       131072          320        92.60      1349.90
       262144          160       169.52      1474.76
       524288           80       274.93      1818.64
      1048576           40       481.37      2077.42
      2097152           20       908.20      2202.16
      4194304           10      1785.11      2240.76


# All processes entering MPI_Finalize

[adm_forai@login-01 ~]$




On 13/11/17 - KW46, 14:21, "users on behalf of Forai,Petar" 
<users-boun...@lists.open-mpi.org on behalf of petar.fo...@imp.ac.at> wrote:

    Hi Jeff!
    
    Thanks for your quick reply. This is a bunch of Cisco UCS C Series machines 
hooked up into an ACI leaf pair. Before the debugging session today we didn’t 
even have unicast routing turned on within the MPI bridge domain for this 
cluster so nothing could reach those IP interfaces before – we’ve observed the 
kernel interfaces that are “attached” to the usnic0 interface and did not see 
any UDP traffic appearing.
    
    We’re suspecting the corruption and dropping going on. When we look at the 
decoded frame there we see the MAC address of the two MPI ranks  (06 02 ff 0c 
1f c2 and 06 02 ff 0c d3 25) but with a bunch of 00 before and after which 
creates the impression here, that this dump is actually multiple frames merged 
into one or something like this. I don’t know the usNIC on wire protocol but 
seeing the MAC multiple times is kind of suspicious for a host to host 
protocol. 
    
    I’ve attached a pcap file of a IMB PingPong that was captured to the APIC 
(GRE encapsed) of that fabric while we observed the frame dump being written to 
the output every now and then. The pcap file looks pretty solid and nothing 
strange there.
    
    Thanks for the hint about this message being harmless so I guess if we 
don’t find anything else we’ll go with a small patch to disable the dumping of 
the frames to the console.
    
    Any other clues? 
    
    best,
    P
    
    Which level of dropping should we expect here actually? Also PFC is turned 
on there and set to class 3 
    
    On 10/11/17 - KW45, 19:53, "users on behalf of Jeff Squyres (jsquyres)" 
<users-boun...@lists.open-mpi.org on behalf of jsquy...@cisco.com> wrote:
    
        On Nov 9, 2017, at 6:51 PM, Forai,Petar <petar.fo...@imp.ac.at> wrote:
        > 
        > We’re observing output such as the following when running non-trivial 
MPI software through  SLURM’s srun
        > 
        > [cn-11:52778] unrecognized payload type 255
        > [cn-11:52778] base = 0x9ce2c0, proto = 0x9ce2c0, hdr = 0x9ce300
        > [cn-11:52778]    0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
        > [cn-11:52778]   10: 00 00 00 00 00 00 06 02 ff 0c 1f c2 06 02 ff 0c
        > [cn-11:52778]   20: b9 8f 08 00 45 00 00 3c 00 00 40 00 08 11 5d 5d
        > [cn-11:52778]   30: 0a 95 00 16 0a 95 00 15 e5 05 e8 d9 00 28 7c 8c
        > [cn-11:52778]   40: 01 00 00 00 00 00 31 b6 00 00 8f e3 00 00 00 00
        > [cn-11:52778]   50: 00 00 00 00 00 00 06 02 ff 0c d3 25 06 02 ff 0c
        > [cn-11:52778]   60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
        > [cn-11:52778]   70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
        > 
        > It is independent of the software BUT is NOT observable when running 
with mpiexec/mpirun.
        
        That is extremely odd.  I cannot think of how the choice of launcher 
would affect the usNIC BTL.
        
        >  When switching to the TCP or vader BTL we have clean output and the 
message is not observed. It is output by different ranks on various nodes, so 
not reproducibly the same nodes.
        > 
        > The location of the message seems to be from here[1] 
        
        Let me take a step back and explain the usNIC BTL: it uses OS-bypass 
UDP for communication.  This means that it is connectionless, and will accept 
datagrams from anywhere.  When the usNIC BTL receives a message, it does a few 
things to verify that it is both an Open MPI frame and from a peer that it 
recognizes.  If the message fails any of the verifications, the usNIC BTL 
simply drops it.
        
        There are two usual reasons that the usNIC BTL ends up dropping a 
message:
        
        1. It was a valid message from a peer, but it got corrupted in transit.
        
        PSA: corrupted packets happen.  Usually the network layer filters them 
out and user-level processes don't see them -- but rarely they can eek through 
and still be received in userspace [with very low frequency].
        
        If a valid message gets dropped, it will simply be re-transmitted by 
the sender a short time later.
        
        2. It was a message from something else (i.e., a non-Open MPI sender).
        
        In my internal Cisco testing, for example, I periodically get frames 
from Cisco IT malware scanners (i.e., they find my open usNIC UDP ports and try 
to send traffic to them).  In these cases, the usNIC BTL dropping the frame is 
the Right Thing To Do.
        
        > Any idea how to get rid of this or what might be the root cause? 
Hints what to check for would be greatly appreciated! 
        
        The messages are actually harmless -- they're just the usNIC BTL 
indicating that it is dropping a message.
        
        But I can see how that would be annoying -- I'll switch the default to 
turn them off by default for future versions (and only turn them on if the user 
specifically requests them).
        
        For an immediate fix, you can basically #if 0 out the block in 
btl_usnic_recv.c that prints out those messages.  The attached patch does that 
and is against v2.0.2, but note that we literally just released v2.0.4 today 
(just additional bug fixes against the v2.0.x series).  Finally, the latest 
released version of Open MPI is v3.0.0, if you feel like upgrading.
        
        -- 
        Jeff Squyres
        jsquy...@cisco.com
        
        
    
    

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