Look here:
http://www.open-mpi.org/faq/?category=tuning#selecting-components
General idea
mpirun -np 2 --mca btl ^tcp (to exclude ethernet) replace with
^openib (or ^mvapi) to exclude infiniband.
Brock Palen
Center for Advanced Computing
bro...@umich.edu
(734)936-1985
On Apr 18, 2007, at 8:44 AM, stephen mulcahy wrote:
Hi,
I'm currently conducting some testing on system with gigabit and
infiniband interconnects. I'm keen to baseline openmpi over both the
gigabit and infiniband interconnects.
I've compiled it with defaults and run the Intel MPI Benchmarks
PingPong
as follows to get an idea of latency and bandwidth between nodes on
the
given interconnect.
~/openmpi-1.2/bin/mpirun --bynode -np 2 --hostfile ~/openmpi.hosts.80
~/IMB/IMB-MPI1-openmpi -npmin 2 pingpong
For some reason, it looks like openmpi is using the infiniband
interconnect rather than the gigabit ... or the system I'm testing on
has an amazing latency! :)
#---------------------------------------------------
# Benchmarking PingPong
# #processes = 2
#---------------------------------------------------
#bytes #repetitions t[usec] Mbytes/sec
0 1000 1.63 0.00
1 1000 1.54 0.62
2 1000 1.55 1.23
4 1000 1.54 2.47
8 1000 1.56 4.90
16 1000 1.86 8.18
32 1000 1.94 15.75
64 1000 1.92 31.77
128 1000 1.99 61.44
256 1000 2.25 108.37
512 1000 2.70 180.88
1024 1000 3.64 267.99
2048 1000 5.60 348.89
I read some of the FAQs and noted that OpenMPI prefers the faster
available interconnect. In an effort to force it to use the gigabit
interconnect I ran it as follows,
~/openmpi-1.2/bin/mpirun --mca btl tcp,self --bynode -np 2 --hostfile
~/openmpi.hosts.80 ~/IMB/IMB-MPI1-openmpi -npmin 2 pingpong
and
~/openmpi-1.2/bin/mpirun --mca btl_tcp_if_include eth0 --mca btl
tcp,self --bynode -np 2 --hostfile ~/openmpi.hosts.80
~/IMB/IMB-MPI1-openmpi -npmin 2 pingpong
Neither one resulted in a significantly different benchmark.
Am I doing something obviously wrong in how I invoke openmpi here or
should I expect this to run over gigabit? Is there an option to mpirun
which I can provide to tell me what interconnect it does use?
I gave a look at the ompi_info output but couldn't see any indication
that infiniband support was compiled in so I'm a little puzzled by
this
but the results speak for themselves.
Any advice on how to force the use of gigabit would be welcomed (I'll
use the infiniband interconnect aswell but I'm trying to determine the
performance to be had from infiniband for our model so I need to
run it
with both).
Thanks,
-stephen
--
Stephen Mulcahy, Applepie Solutions Ltd., Innovation in Business
Center,
GMIT, Dublin Rd, Galway, Ireland. +353.91.751262 http://
www.aplpi.com
Registered in Ireland (289353) (5 Woodlands Avenue, Renmore, Galway)
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