One thing that changed between 1.6 and 1.8 is the default binding policy. Open MPI 1.6 did not bind by default but 1.8 binds to core. You can unset the binding policy by adding --bind-to none.
-Nathan Hjelm HPC-5, LANL On Tue, Dec 09, 2014 at 12:14:32PM -0500, Eric Chamberland wrote: > Hi, > > we were used to do oversubscribing just to do code validation in nightly > automated parallel runs of our code. > > I just compiled openmpi 1.8.3 and launched the whole suit of > sequential/parallel tests and noticed a *major* slowdown in oversubscribed > parallel tests with 1.8.3 compared to 1.6.5. > > For example, on my computer (2 cpu), a validation test of 64 processes > launched with 1.8.3 took 1500 seconds (~29 minutes) to execute, while the > very same test compiled with 1.6.5 took only 7.4 seconds! > > To have this result with 1.6.5 we had to set the variable > "OMPI_MCA_mpi_yield_when_idle=1", but it seems to have no effects in 1.8.3 > when I launch more processes than number of core in my computer, even if it > is still mentioned to work (see > http://www.open-mpi.org/faq/?category=running#force-aggressive-degraded). > However, when I launch with fewer processes than number of core, then it is > faster without "OMPI_MCA_mpi_yield_when_idle=1", which is the same behavior > in 1.6.5. > > I tried to launch with a host file like this: > > localhost slots=2 > > but it changed nothing... > > What do I do wrong? > > Is it possible to retrieve "performances" of 1.6.5 for oversubscription? > > Is there a compilation option that I have to enable in 1.8.3? > > Here are the config.log and "ompi_info --all" files for both versions of > mpi: > > http://www.giref.ulaval.ca/~ericc/ompi_bug/config.165.log.gz > http://www.giref.ulaval.ca/~ericc/ompi_bug/config.183.log.gz > http://www.giref.ulaval.ca/~ericc/ompi_bug/ompi_info.all.165.txt.gz > http://www.giref.ulaval.ca/~ericc/ompi_bug/ompi_info.all.183.txt.gz > > Thanks, > > Eric > > > > > _______________________________________________ > users mailing list > us...@open-mpi.org > Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users > Link to this post: > http://www.open-mpi.org/community/lists/users/2014/12/25936.php
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