ISBN 978-82-326-2422-5 (printed ver.) ISBN 978-82-326-2423-2 (electronic ver.) ISSN 1503-8181 ...

201 Pages·2017·3.61 MB·English

by  Alexandru Ciprian Iordan

Doctoral theses at NTNU, 2017:175
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ISBN 978-82-326-2422-5 (printed ver.)
ISBN 978-82-326-2423-2 (electronic ver.)
ISSN 1503-8181
Doctoral theses at NTNU, 2017:175 NTNUniversity of Science and TechnologyThesis for the Degree ofPhilosophiae Doctorormation Technology and ElectricalEngineeringDepartment of Computer Science
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Alexandru Ciprian Iordan
Improving the Energy-Efficiency
of Task Based Programming on
Chip Multiprocessors
Thesis for the Degree of Philosophiae Doctor
Trondheim, June 2017
Norwegian University of Science and Technology
Faculty of Information Technology and Electrical Engineering
Department of Computer Science
NTNU
Norwegian University of Science and Technology
Thesis for the Degree of Philosophiae Doctor
Faculty of Information Technology and Electrical Engineering
Department of Computer Science
© Alexandru Ciprian Iordan
ISBN 978-82-326-2422-5 (printed ver.)
ISBN 978-82-326-2423-2 (electronic ver.)
ISSN 1503-8181
Doctoral theses at NTNU, 2017:175
Printed by NTNU Grafisk senter
Tomylovingwifeandourbeautifulchildren.

Abstract
In the early 2000s, the superscalar CPU paradigm reached the point of diminishing re-
turnsmainlyduetopowerrequirementsandoverheatingconcerns.Facedwithaconstant
demand for performance, hardware developers were in need of new ways to efficiently
use the ever increasing transistor count predicted by Moore’s law. The Chip MultiPro-
cessors(CMPs)cameasanaturalsolutiontothepowerwall: severallesscomplexand
significantly less "power hungry" cores integrated on a single chip. In almost all ICT
segmentstoday,fromHighPerformanceComputing(HPC)toembeddeddevices,CMPs
havebecomethearchitectureofchoice. WiththiswideadoptionofCMPs,softwarede-
velopers need to use parallel programming to fully exploit this architecture. Although
parallelizationcanmaximizetheperformanceandenergyefficiencyofapplicationsrun-
ning on CMPs, it also comes with its own set of challenges. Among these, inherent
managementoverheadsthatcanaccountforsub-linearspeedupsandcanincreasetheen-
ergyconsumptionofexecutions. Becauseofrisingconcernsforenergycostandbattery
life,muchresearchanddevelopmenttodayfocusesonreducingpowerrequirementsand
savingenergy.
In this thesis, we investigate how parallel programming can be used to improve the en-
ergy efficiency of applications running on CMP systems. We focus on a programming
paradigmcalledTaskBasedProgramming(TBP).ThebaseconceptoftheTBPmodelis
thattheprogrammerfocusesonidentifyingandannotatingpiecesofcode(tasks)which
can be executed concurrently with other tasks. An important result of our work is an
increased understanding of how computations, parallelization and energy consumption
relatewhenexecutingonCMPsystems.
Working in this direction, we use a simulation framework to allow for increased flex-
ibility in design space exploration and noninvasive measurements. Unfortunately, the
performanceoverheadofsimulationissignificant: simulatingaparallelapplicationcan
be 10000x slower than executing it on real hardware. In the first part of our research,
wetookituponourselvestotrytosolvethisissue. Weinvestigatethechallengesofem-
ploying a sampling based technique to take advantage of the periodic behavior in TBP
parallelapplications. Ourproposalisasimple3-phasemethodologythatidentifiesonly
asmallnumberofrepresentativeexecutionsamplestosimulatethusreducingtheoverall
simulationtime.
In the second part of our work, we look at parallelization as a mean to save energy on
CMPplatforms. WetestandcomparetwoTBPlibraries,WoolandIntelTBB,focusing
onthebehaviorofsomebasicTBPparallelizationoperationsliketaskspawning,tasksyn-
chronizationandtaskstealing.Weinvestigatetheenergyfootprintoftheseparallelization
overheadsandtheeffectithasontheenergy-efficiencyoftheexecutingsystem.Wehave
identifiedthatfailedtaskstealsamountforthelargestoverhead. Toreducetheirimpact
and improve our system’s energy efficiency, we devised a new occupancy-aware policy
forvictimselection. Thispolicyallowsforamoreinformeddecisionwhenselectingthe
victimfortaskstealingandreducesthenumberoffailedsteals.
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Preface
This doctoral thesis was submitted to the Norwegian University of Science and Tech-
nology(NTNU)inpartialfulfillmentoftherequirementsforthedegreeofphilosophiae
doctor(PhD).TheworkhereinwasperformedattheDepartmentofComputerandInfor-
mationScience(IDI),NTNU,underthesupervisionofProfessorLasseNatvig.
This thesis consists of two parts. The first part consists of introduction, background,
methodology,researchprocess,asummaryofpapersandfinalconclusions. Thesecond
partisthemaincontribution,presentedasacollectionofsixresearchpapers.
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Acknowledgements
Nodeedisachievedsingle-handedlyandtheworkforthisthesisisnoexception. There
aresomanypeoplethatIneedtothankfortheirsupport,guidance,orsimplybeingthere
withmethroughoutmyPhDexperience.
First,IwouldliketothankmysupervisorProf.LasseNatvigforhisadviceandguidance
duringmyNorwegianadventurethatbecamethisthesis.FromthefirsteveningwhenIar-
rivedinTrondheimandhepickedmeupfromtheairportbus,itwashishelpandconstant
support that made me stay on track. Thank you for being patient with my many ideas
and (slow) investigations, but also for pulling me back when I was a bit too ambitious.
I also extend my gratitude to my co-supervisors, Prof. Per Gunnar Kjeldsberg and Dr.
Gaute Myklebust for providing valuable feedback and encouragement in my evaluation
meetings.
I also owe a great deal of gratitude to Magnus Jahre for his help beyond and above my
academic work. He was my “person to go to” for any issues that I faced, research or
otherwise, and he always provided me with good insight. Thank you for the countless
slabberas1meetingsandforhelpingmegoovertheculturalbarier.
IwouldliketothankmycolleaguesatthedepartmentofComputerandInformationSci-
ence throughout the years: Kostas, Dragana, Asbjorn, Stefano, Ian, Nico, Yaman, Jan-
Christian, Abdullah, Nikita, Juan Manuel, Odd Rune and many others. Thank you for
providingagreatworkingenvironmentwithcountlessinteresting,engaginganddiverse
discussions.
IwouldliketothankAnaLuciaVarbanescuforfirstsuggestingmethePhDpositionat
NTNU.Hersupportandguidanceinpreparingfortheinterviewwasinvaluableaswellas
alltheadvicessheprovidedeversince.
I also need to thank Prof. Radu Varbanescu for introducing me to all the wonders and
perilsofacademicresearch. Itwashissupportduringmybachelorandmasterstudiesin
RomaniathatgotmetothepointwhereIwantedandwasabletodoPhDwork.
Finally, I would like to thank my family. To my parents and parents-in-law thank you
for all the help and support in making sure I do not feel alone far away from my home
country.Yourvisitsandcarepackagesovertheyearshavemeantalotforme.However,to
mylovingwifeCristinaIowemaybethemost.Withoutherrelentlesssupportbeforeand
duringmyPhDwork,noneofitwouldhavebeenpossible. AndalsoIshouldnotforget
tomentionourtwobeautifulchildren,DavidandMatei,whomadesureIhadsomething
todooutsidemywork.
1Norwegian:slabberas-pleasantconversationoverteaorcoffee
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