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I wonder why ch3:nemesis or ch3:ssm is the default in MPICH. Why ch3:socket?<div><br></div><div>Robert</div><div><br></div><div><div><div>On Jul 2, 2008, at 10:59 PM, Rajeev Thakur wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"> <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> <blockquote style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px solid; MARGIN-RIGHT: 0px"> <div class="OutlookMessageHeader" lang="en-us" dir="ltr" align="left"> <hr tabindex="-1"> <font face="Tahoma" size="2"><b>From:</b> owner-mpich-discuss@mcs.anl.gov [<a href="mailto:owner-mpich-discuss@mcs.anl.gov">mailto:owner-mpich-discuss@mcs.anl.gov</a>] <b>On Behalf Of </b>Ariovaldo de Souza Junior<br><b>Sent:</b> Wednesday, July 02, 2008 3:15 PM<br><b>To:</b> <a href="mailto:mpich-discuss@mcs.anl.gov">mpich-discuss@mcs.anl.gov</a><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></blockquote></div><br></div></body></html>