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National Conference on Recent Research in Engineering and Technology (NCRRET -2015) International Journal of Advance Engineering and Research Development (IJAERD) e-ISSN: 2348 - 4470 , print-ISSN:2348-6406

Comparison of Dynamic Scheduling Algorithm for Real Time Operating System HemangThakar AssistantProfessor,CSED e pa rt m ent DJ MIT Abstract—Real timesystem isdivided in to two algorithms static and dynamic. Both algorithmwant to complete his job in givendeadline or before deadline but no onealgorithmare successfullycompletehis jobin overloadedandunderloadedsituation.

Dynamicalgorithmabletogive optimalresultinunderloaded situationbut not abletogivesame resultinov er-loaded situation.Staticalgorithmnotabletogiveoptimalresultinunderloadedsituation butabletoperformw ell inover-loaded s ituation.

Sowethinknewalgorithmtogiveresultoptimuminunder-loaded situation andgivehigh resultin ov er-loadedsituation. We are serving dynamic scheduling algorithms like EDF (Earlierdead line first), M LF (M inimum Laxity First) and RM algorithms perform well in overloaded situation. Here servingthat EDF, M LFandRM algorithms togiveares ultinunder-loadedsituation and inoverloaded situation.

Keywords—EDF,M LF TimeOperatingSystems.

and

RM Scheduling Algorithms,Real-

I. I N T R O D U C T I O N Real-time systemshave well classify, fixedt ime limit.

Mainlytwotypesofreal-t ime systemavailable hardandsoft.

Wherehardrealtimesystemworkonprincipal job must complete theirexecution beforedeadline.

Itsusefulwhere missingdeadlinemaybeseriousconsideration.

Softrealtime systemismoreflexible wh ichallowjobtoexecutionbeyond thedeadline.Itsapplicablewherecostofjobis moreimportant thancansequencesofmissingdeadline.

A.Real-TimeScheduler Generally itsworkedintwocategories staticanddynamic.

Incaseofstaticalgorithm itsappliedpriorit iesatinitial (design)levelandremainsamethroughout thetask.Incaseof dynamicalgorith mpriorityassignon runtimewh ichdepended on parameters o f task. We can make dynamic scheduling withstaticprioritywhereRateMonotonic (RM)andEarliest DeadlineFirst(EDF)andMinimu mlaxitytimeFirst(MLF) are belongsto dynamicschedulingwithdynamicpriority.Here indynamicpriorityalgorith mareimp lements incategories first.Inwhichjobtochangeprioritydaring itisactivation and inanother typejobcannotabletochangepriority.

EDFisjob levelfixedprio rityalgorithmo fthiscategory.Anothersidejob canchange priorityduringexecutioncalled jobleveldynamic priorityalgorith m. M inimu m laxitytimealgorith m belongsto it.Attimet,theslacktimeofajobis(d-t),wheredis thejobsdeadlineandtisitsremainingexecutionrequirement.

Here,theslacktimeisthegreatestamountoftimeajob may berequiredtowaitifitweretoperformonaprocessorandstill meet itsdeadline.TheMLFalgorith ms givehigherpriorityto jobswithsmaller slacktime.Sincetheslacktimeofajobcan modifyovertime,thejobprioritiescanmodifydynamically.

II.T HE D Y NA MI CS CHE DUL IN GA L GORIT HM A.EDFSchedulingAlgorith m EDF Scheduling Algorithm is called earliest dead line first ornearestdeadlinefirst SchedulingAlgorithm.EDFis dynamicSchedulingalgorith m.Thetaskwiththeearliestdead linehasthemaximu mpriority[1].EDFSchedulingAlgorith m gives100percenttaskutilization whensystemisinunder loadedsituationorU¡=1Butwhentaskutilization crossload factormorethen1orslightlyoverloaded processorutilization decreasesexponentially[4].

B.RMSchedulingAlgorithm RMScheduling Algorith miscalled RateMonotonic Algorithm.RM isafixed orstaticpriorityschedulingalgorithm.

RMassignspriorities totasksbasedontheirperiods[4].

Disadvantage ofthisalgorithmisthattheyarenotgive100 percentresultinunderloadedsituation [6].RMgivesbetter performance inoverloadedsituationascomparetodynamic scheduling.InRMalgorith mshortestperiodgivesfirstchances to execute but whenmorethanonetaskhaveSameperiodthen RMarbit rarilyselectsoneforcompletingafterthat[7].

C.M LFSchedulingAlgorith m MLFScheduling AlgorithmiscalledMinimu mlaxityfirst Algorith m.

M LFalsoDynamicScheduling algorithm.Here differencebetweendeadline(d)andexecutiontime(c)iscalled laxity(l).InMLFalgorith msmallestlaxitygiveshighestpriority[8][9].But inMLF more thanonetaskhave same deadline atthattimeM LFselecttaskrandomly.M LFalgorith mgives 100percentresultinunderloadedsituation meanslessthan1 loadfactor.Butwhentaskutilization crossloadfactormore then1orslightlyoverloaded processorutilizationdecreases exponentially[4].

III.S I MUL AT IONRE SULT S Wearesurveyingallalgorith msinsamesimu lator.Herewe arecomparingforallthisalgorithms EDF,M LFand RM.EDF, MLFareDynamicPriorityScheduling Algorith ms andRMis StaticPriorityScheduling Algorith m. WearegeneratingOne task setand task sethas 5periodictask also task setiscompile for100clockcycle.Tousethisallalgorith m wecalculate successratio(SR)andEffectiveProcessorUtilisation(EPU).

1)InRealtimeeverytaskshouldbemeettheredeadline.

SoSuccessRatio meanscalculate howmanytaskmeetthere deadline.

Nu mb e ro fjobessuccess fu ll ys chedu led SR= Tot alnu mb e ro farriv ed 2) In EPUis calculate how many task can Effectively Processorareused.

XVi EPU= T i R

I V.F I NALRE SULT Wehavetakenforallthisalgorith msresultEDF,M LF andRM.Heretasksetstarting0.5andending1.5asshown intable1.Wecalcu late SuccessRatioandEffective Processor Utilizat ionforallthisalgorith m.Wecalcu lateresultunderload andoverloadcondition.

EDFandMLFgives100percentage resultsin underloadconditionbut overloadedconditionit givespoorresultandRMdontgive100percentage resultin underloadedcondition butitgivebetterresultinoverloaded condition.

Figure1showsevaluation oftheresultofSuccessRatio (SR)forEDF,M LFandRMalgorith ms.

Theresultsaretaken fro munder-loadedsituationtotheoverloadedsituation.

Figure2showsevaluationoftheresult ofEffectiveProcessorUtilization (EPU)forEDF,M LFandRMalgorith ms.

The resultsaretakenfromunder-loadedsituationtotheoverloaded situation.

V.C O N C L U S I O N Thealgorith m talksaboutinthischapteraredynamic scheduling algorithms with dynamic and staticpriority for real-t ime singleprocessor systems.

EDF and M LF are dynamicscheduling algorith ms with dynamic priority, whileRM isdynamicschedulingalgorithmwithstaticpriority.

Wecanterminatefollowingfro mtheresultsgainedthrough imitation •

Inunder-loadedsituation. ◦ EDFandMLFshowbestperformance. ◦ PerformanceofRMstarttodegradeafterload 0.85slightly.

•

Inoverloadedsituation. ◦ PerformanceofEDFandM LFstartstodegradedrastically asasystemgoestowards overloadedsituation. ◦ While RMalgorith m perform well still in overloadedsituation.

R E FE RE N CE S

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