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Subject: Re: [OMPI users] Sandy Bridge performance question
From: Jeff Squyres (jsquyres) (jsquyres_at_[hidden])
Date: 2013-06-07 08:00:26


+1

Depending on how much you care, you might also want to look at some performance analysis tools to look and see what is happening under the covers. The Intel VTune suite is the gold standard -- it shows all the counters and statistics from the CPUs themselves (be aware that there's a bit of a learning curve) -- to include things like cache statistics, instructions per clock, ...etc. Lots and lots and lots of info.

Other tools are good, too -- google around (e.g., the cachegrind tool in valgrind, etc.).

On Jun 6, 2013, at 4:42 PM, Ralph Castain <rhc_at_[hidden]> wrote:

> 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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>
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-- 
Jeff Squyres
jsquyres_at_[hidden]
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