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From: Alex Tumanov (atumanov_at_[hidden])
Date: 2007-02-08 12:02:22


Hello Jeff. Thanks for pointing out NetPipe to me. I've played around
with it a little in hope to see clear evidence/effect of message
striping in OpenMPI. Unfortunately, what I saw is that the result of
running NPmpi over several interconnects is identical to running it
over a single fastest one :-( That was not the expected behavior, and
I'm hoping that I'm doing something wrong. I'm using NetPIPE_3.6.2
over OMPI 1.1.4. NetPipe was compiled by making sure Open MPI's mpicc
can be found and simply running 'make mpi' under NetPIPE_3.6.2
directory.

I experimented with 3 interconnects: openib, gm, and gig-e.
Specifically, I found that the times (and, correspondingly, bandwidth)
reported for openib+gm is pretty much identical to the times reported
for just openib. Here are the commands I used to initiate the
benchmark:

# mpirun -H f0-0,c0-0 --prefix $MPIHOME --mca btl openib,gm,self
~/NPmpi > ~/testdir/ompi/netpipe/ompi_netpipe_openib+gm.log 2>&1
# mpirun -H f0-0,c0-0 --prefix $MPIHOME --mca btl openib,self ~/NPmpi
> ompi_netpipe_openib.log 2>&1

Similarly, for tcp+gm the reported times were identical to just
running the benchmark over gm alone. The commands were:
# mpirun -H f0-0,c0-0 --prefix $MPIHOME --mca btl tcp,gm,self --mca
btl_tcp_if_exclude lo,ib0,ib1 ~/NPmpi
# mpirun -H f0-0,c0-0 --prefix $MPIHOME --mca btl gm,self ~/NPmpi

Orthogonally, I've also observed that trying to use any combination of
interconnects that includes openib (except using it exclusively) fails
as soon as the benchmark reaches trials with 1.5MB message sizes. In
fact the CPU load remained at 100% on the headnode, but no further
output is sent to the log file or the screen (see the tails below).
This behavior is fairly consistent and may be of interest to Open MPI
development community. If anybody has tried using openib in
combination with other interconnects please let me know what issues
you've encountered and what tips and tricks you could share in this
regard.

Many thanks. Keep up the good work!

Sincerely,
Alex.

Tails (the log file name reflects the combination of interconnects in
that CL order):
# tail ompi_netpipe_gm+openib.log
101: 786432 bytes 38 times --> 3582.46 Mbps in 1674.83 usec
102: 786435 bytes 39 times --> 3474.50 Mbps in 1726.87 usec
103: 1048573 bytes 19 times --> 3592.47 Mbps in 2226.87 usec
104: 1048576 bytes 22 times --> 3515.15 Mbps in 2275.86 usec
105: 1048579 bytes 21 times --> 3480.22 Mbps in 2298.71 usec
106: 1572861 bytes 21 times --> 4174.76 Mbps in 2874.41 usec
107: 1572864 bytes 23 times --> mpirun: killing job...

# tail ompi_netpipe_openib+gm.log
100: 786429 bytes 45 times --> 3477.98 Mbps in 1725.13 usec
101: 786432 bytes 38 times --> 3578.94 Mbps in 1676.47 usec
102: 786435 bytes 39 times --> 3480.66 Mbps in 1723.82 usec
103: 1048573 bytes 19 times --> 3594.26 Mbps in 2225.76 usec
104: 1048576 bytes 22 times --> 3517.46 Mbps in 2274.37 usec
105: 1048579 bytes 21 times --> 3482.13 Mbps in 2297.45 usec
106: 1572861 bytes 21 times --> mpirun: killing job...

# tail ompi_netpipe_openib+tcp+gm.log
100: 786429 bytes 45 times --> 3481.45 Mbps in 1723.41 usec
101: 786432 bytes 38 times --> 3575.83 Mbps in 1677.93 usec
102: 786435 bytes 39 times --> 3479.05 Mbps in 1724.61 usec
103: 1048573 bytes 19 times --> 3589.68 Mbps in 2228.61 usec
104: 1048576 bytes 22 times --> 3517.96 Mbps in 2274.05 usec
105: 1048579 bytes 21 times --> 3484.12 Mbps in 2296.14 usec
106: 1572861 bytes 21 times --> mpirun: killing job...

# tail -5 ompi_netpipe_openib.log
119: 6291456 bytes 5 times --> 4036.63 Mbps in 11891.10 usec
120: 6291459 bytes 5 times --> 4005.81 Mbps in 11982.61 usec
121: 8388605 bytes 3 times --> 4033.78 Mbps in 15866.00 usec
122: 8388608 bytes 3 times --> 4025.50 Mbps in 15898.66 usec
123: 8388611 bytes 3 times --> 4017.58 Mbps in 15929.98 usec