It depends on the application you are using. Some are "balanced" - i.e., they run faster if the number of processes is a power of two. You'll see that n8 is faster than n7, so this is likely the situation.
On Jun 6, 2013, at 4:10 PM, "Blosch, Edwin L" <edwin.l.blo...@lmco.com> wrote: > I am running single-node Sandy Bridge cases with OpenMPI and looking at > scaling. > > I’m using –bind-to-core without any other options (default is –bycore I > believe). > > These numbers indicate number of cores first, then the second digit is the > run number (except for n=1, all runs repeated 3 times). Any thought why n15 > should be so much slower than n16? I also measure the RSS of the running > processes, and the rank 0 process for n=15 cases uses about 2x more memory > than all the other ranks, whereas all the ranks use the same amount of memory > for the n=16 cases. > > Thanks for insights, > > Ed > > n1.1: 6.9530 > n2.1: 7.0185 > n2.2: 7.0313 > n3.1: 8.2069 > n3.2: 8.1628 > n3.3: 8.1311 > n4.1: 7.5307 > n4.2: 7.5323 > n4.3: 7.5858 > n5.1: 9.5693 > n5.2: 9.5104 > n5.3: 9.4821 > n6.1: 8.9821 > n6.2: 8.9720 > n6.3: 8.9541 > n7.1: 10.640 > n7.2: 10.650 > n7.3: 10.638 > n8.1: 8.6822 > n8.2: 8.6630 > n8.3: 8.6903 > n9.1: 9.5058 > n9.2: 9.5255 > n9.3: 9.4809 > n10.1: 10.484 > n10.2: 10.452 > n10.3: 10.516 > n11.1: 11.327 > n11.2: 11.316 > n11.3: 11.318 > n12.1: 12.285 > n12.2: 12.303 > n12.3: 12.272 > n13.1: 13.127 > n13.2: 13.113 > n13.3: 13.113 > n14.1: 14.035 > n14.2: 13.989 > n14.3: 14.021 > n15.1: 14.533 > n15.2: 14.529 > n15.3: 14.586 > n16.1: 8.6542 > n16.2: 8.6731 > n16.3: 8.6586 > ~ > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users
