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Subject: Re: [OMPI users] Sandy Bridge performance question
From: Ralph Castain (rhc_at_[hidden])
Date: 2013-06-06 19:42:57


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.blosch_at_[hidden]> 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
> ~
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