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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>What kind of network utilization do you have going? Are the
results from a single machine using local I/O for input and output? There are
lots of variables that can impact the performance. My first guess would be
that you have some distribution issues/efficiency issues that are exposed when
trying to distribute that you are covering when running on a single machine.
You might start by profiling the network and see if that is a constriction
issue or if you have issues of contention with network accessible disk.<o:p></o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> mpich-discuss-bounces@mcs.anl.gov
[mailto:mpich-discuss-bounces@mcs.anl.gov] <b>On Behalf Of </b>Norman Geist<br>
<b>Sent:</b> Wednesday, June 23, 2010 1:28 AM<br>
<b>To:</b> mpich-discuss@mcs.anl.gov<br>
<b>Subject:</b> [mpich-discuss] Some questions for understanding<o:p></o:p></span></p>
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<p class=MsoNormal style='background:white'><span style='font-size:9.0pt;
font-family:"Verdana","sans-serif";color:black'> Hello,<br>
<br>
my name is Norman, and i administrate a 32x FSC Primergy-Cluster installed with
OpenSuse, SunGridEngine, MPICH and linked with Gigabit-Ethernet. Its used for
executing scientific scripts on a cpmd.x or sander.mpi with a input file of
atoms. If i run such a job on one machine=4cpus, it runs with nearly 100 %. BUt
if i now run the same job on 8 cpus=2 machines, the average goes down to close
under 50 %. Means one machine alone is faster than 2 machines. But i think the
sense of a cluster is to bundle the cpu-power, or not?? Am I right when i
suppose that mpi does only work when the programmer himself splitt the tasks in
his programm or script with MPI-Commands?<br>
<br>
It complicated =)! Or could it be that while compiling a programm for example
the normal routines, operators and functions are replaced with mpi-functions
which have the communication routines within, so that the comiled programm
example.x can itself can communicate??? But if, how the program know with which
machine it shell cooperate.<br>
<br>
Firstly i though that maybe the job isn't cooperating but executed on f.e. two
machines seperately, but the output files are normal, no dublicates or
something.<br>
<br>
Please help me to understand the real mechanics of mpich so i can try to
optimze my cluster to execute jobs on multible machines with a good average.<br>
<br>
Thank you very much.<o:p></o:p></span></p>
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<p class=MsoNormal style='line-height:12.75pt'><span style='font-size:9.0pt;
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