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Title
Modelling parallel overhead from simple run-time records
AuthorHöfinger, Siegfried ; Haunschmid, Ernst
Published in
The Journal of Supercomputing, 2017, Vol. 73, Issue 10, page 4390-4406
Published2017
LanguageEnglish
Document typeJournal Article
Keywords (EN)HPC / MPI / Parallel overhead / Performance modelling / mpiP / allinea/MAP
ISSN1573-0484
URNurn:nbn:at:at-ubtuw:3-4151 Persistent Identifier (URN)
DOI10.1007/s11227-017-2023-9 
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 The work is publicly available
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Abstract (English)

A number of scientific applications run on current HPC systems would benefit from an approximate assessment of parallel overhead. In many instances a quick and simple method to obtain a general overview on the subject is regarded useful auxiliary information by the routine HPC user. Here we present such a method using just execution times for increasing numbers of parallel processing cores. We start out with several common scientific applications and measure the fraction of time spent in MPI communication. Forming the ratio of MPI time to overall execution time we obtain a smooth curve that can be parameterized by only two constants. We then use this two-parameter expression and extend Amdahls theorem with a new term representing parallel overhead in general. Fitting the original data set with this extended Amdahl expression yields an estimate for the parallel overhead closely matching the MPI time determined previously.

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CC-BY-License (4.0)Creative Commons Attribution 4.0 International License