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<DIV dir=ltr align=left><SPAN class=812315802-03072008><FONT face=Arial
color=#0000ff size=2>For best performance, configure with
--with-device=ch3:nemesis. It will use the Nemesis device within MPICH2 that
communicates using shared memory within a node and TCP across
nodes.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=812315802-03072008><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=812315802-03072008><FONT face=Arial
color=#0000ff size=2>Rajeev</FONT></SPAN></DIV><BR>
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<FONT face=Tahoma size=2><B>From:</B> owner-mpich-discuss@mcs.anl.gov
[mailto:owner-mpich-discuss@mcs.anl.gov] <B>On Behalf Of </B>Ariovaldo de
Souza Junior<BR><B>Sent:</B> Wednesday, July 02, 2008 3:15 PM<BR><B>To:</B>
mpich-discuss@mcs.anl.gov<BR><B>Subject:</B> [mpich-discuss] core 2 quad and
other multiple core processors<BR></FONT><BR></DIV>
<DIV></DIV>Hello everybody!<BR><BR>I'm really a newbie on clustering, so I
have some, let's say, stupid questions. When I'm starting a job like this
"mpiexec -l -n 6 ./cpi" in my small cluster of (until now) 6 core 2 quad
machines, I'm sending 1 process to each node, right? Assuming that I'm
correct, each process will utilize only 1 core of each node? and how to make 1
process run utilizing the whole processing capacity of the processor, the 4
cores? is there a way to do this? or I'll always utilize just one processor
for each process? if I change this submission to "mpiexec -l -n 24 ./cpi" then
the same process will run 24 times, 4 times per node (maybe simultaneously)
and one process per core, right?<BR><BR>I'm asking all this because I think it
is a bit strange to see the processing time increasing each time I put one
more process to run, once in my mind it should be the contrary. I'll give some
examples:<BR><BR>mpiexec -n 1 ./cpi<BR>wall clock time =
0.000579<BR><BR>mpiexec -n 2 ./cpi<BR>wall clock time =
0.002442<BR><BR>mpiexec -n 3 ./cpi<BR>wall clock time =
0.004568<BR><BR>mpiexec -n 4 ./cpi<BR>wall clock time =
0.005150<BR><BR>mpiexec -n 5 ./cpi<BR>wall clock time =
0.008923<BR><BR>mpiexec -n 6 ./cpi<BR>wall clock time =
0.009309<BR><BR>mpiexec -n 12 ./cpi<BR>wall clock time =
0.019445<BR><BR>mpiexec -n 18 ./cpi<BR>wall clock time =
0.032204<BR><BR>mpiexec -n 24 ./cpi<BR>wall clock time =
0.045413<BR><BR>mpiexec -n 48 ./cpi<BR>wall clock time =
0.089815<BR><BR>mpiexec -n 96 ./cpi<BR>wall clock time =
0.218894<BR><BR>mpiexec -n 192 ./cpi<BR>wall clock time = 0.492870<BR><BR>So,
as you all can see is that as more processes I add, more time it takes, what
makes me think that mpi is performing this test 192 times in the end and due
to this the time increased. Is that correct that mpi performed the same test
192? Or did it divide the process into 192 pieces, calculated and then
gathered the results and mounted the output again? I really would like to
understand this relationship processor # x process # x .<BR><BR>I have the
feeling that my questions are a bit "poor" and really from a newbie, but the
answer will help me on utilizing other programs that will need mpi to
run.<BR><BR>Thanks to all!<BR><BR>Ari - UFAM -
Brazil<BR><BR></BLOCKQUOTE></BODY></HTML>