Dear Pascal,<br><br>I've been playing with both for some time. From the point of view of efficiency, it seens to me that mpi is at the moment better paralellized, which means you get a faster calculation with the same number of processors. However there's a big drawback in pure mpi: each process has it's own memory requirements, which means you might get in a situation where your total number of processors is limited by the memory available in the supercomputer node. In this situation, OpenMP is nice; running a job with 1 processor and with 8 under OpenMP increases the memory requirements much less than with MPI, which in practice allows you to run with more processors.<br>
<br>I believe that the hybrid scheme is preferable when you have a computer architecture that demands it. For example, a cluster of networked PCs, each node containing 8 cores, without shared memory. In this case, you could spawn a mpi process for each node, and run them with openmp to use the cores without overloading the memory. <br>
<br>If on the other hand you are using a supercomputer with shared memory, then you can simply go for pure MPI if the machine can handle it.<br><br>Regards<br><br clear="all">Giovani M. Faccin<br>UFMS / Brazil<br>
<br><br><div class="gmail_quote">2011/10/12 pascal boulet <span dir="ltr"><<a href="mailto:pascal.boulet@univ-provence.fr">pascal.boulet@univ-provence.fr</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Dear all,<br>
<br>
<br>
I am not familiar with the openMP parallelization. I would like to know<br>
in what circumstances openMP is worth being used? Same question for<br>
MPI+openMP.<br>
<br>
Thank you for your help.<br>
Best regards<br>
Pascal<br>
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