Systems composed of distinct operational modes are a common necessity for embedded applications with strict timing
requirements. With the emergence of multi-core platforms protocols to handle these systems are required in order to
provide this basic functionality.In this work a description on the problems of creating an effective mode-transition
protocol are presented and it is proven that in some cases previous single-core protocols can not be extended to handle
the mode-transition in multi-core

Marinho, José

Nélis, Vincent

Petters, Stefan M.

Raravi, Gurulingesh

Repositório Científico do Instituto Politécnico do Porto

        Partitioned Scheduling of Multimode Systems on Multiprocessor Platforms: when to do the Mode Transition?     www.hurray.isep.ipp.pt Technical Report HURRAY-TR-110701 Version:  Date: 07-13-2011 José Marinho Gurulingesh Raravi Vincent Nélis Stefan M. Petters  Technical Report HURRAY-TR-110701             Partitioned Scheduling of Multimode Systems on Multiprocessor Platforms:                                                                                    when to do the Mode Transition? © IPP Hurray! Research Group www.hurray.isep.ipp.pt   1  Partitioned Scheduling of Multimode Systems on Multiprocessor Platforms: when to do the Mode Transition? José Marinho, Gurulingesh Raravi, Vincent Nélis, Stefan M. Petters IPP-HURRAY! Polytechnic Institute of Porto (ISEP-IPP) Rua Dr. António Bernardino de Almeida, 431 4200-072 Porto Portugal Tel.: +351.22.8340509, Fax: +351.22.8340509 E-mail:  http://www.hurray.isep.ipp.pt  Abstract Systems composed of distinct operational modes are a common necessity for embedded applications with strict timing requirements. With the emergence of multi-core platforms protocols to handle these systems are required in order to provide this basic functionality.In this work a description on the problems of creating an effective mode-transition protocol are presented and it is proven that in some cases previous single-core protocols can not be extended to handle the mode-transition in multi-core.  Partitioned Scheduling of Multimode Systems on Multiprocessor Platforms: whento do the Mode Transition?Jose´ Marinho, Gurulingesh Raravi, Vincent Ne´lis, Stefan M. PettersCISTER-ISEP Research Center, Polytechnic Institute of Porto, Portugal.{jmsm, ghri, nelis, smp}@isep.ipp.ptConsider the problem of executing a multimode real-time system using partitioned scheduling on a multipro-cessor platform. The model of computation is as follows(all technical terms are interpreted according to their usualdefinitions):• Platform: The platform is composed of m identicalprocessors {π1, . . . ,πm}.• System: The system is composed of a task setτ = {τ1, τ2, . . . , τn}, where each task is assumedto be sporadic and implicit-deadline. The n tasks aredivided into k subsets {τ1, τ2, . . . , τk}, where eachsubset τ j represents the tasks that have to be executedwhile the system is running in mode Mj . The systemcan run in k different operational modes. Thesesubsets τ j are exhaustive but not mutually exclusive,i.e., τ1 ∪ τ2 ∪ . . . ∪ τk = τ and ∃j, i : τ i ∩ τ j ￿= ∅.The tasks belonging to more than one mode are calledMode-Independent (MI) tasks.• Mode Transition: At run-time, the application iseither running in one of the modes (say Mi) or itis switching from one mode (i.e., the old mode) toanother (i.e., new mode). A mode transition phasestarts with a Mode Change Request (MCR) and endswhen all the old mode tasks have completed theexecution of their last released job (those old modetasks do not release new jobs after an MCR) andall the new mode tasks have been activated, i.e.they have started to release jobs. Note that a mode-independent task that belongs to both the old andnew mode should not be affected by the mode changein progress. Additionally no deadlines in the systemmay be violated.• Scheduling: We consider partitioned scheduling, i.e.,the task set τ j of each mode M j is partitioned intom subsets τ j,1, τ j,2, . . . , τ j,m. Each partition τ j,￿ isstatically assigned to processor π￿ and is scheduledby preemptive EDF.• Assumptions: Tasks are not allowed to migrate be-tween processors during the execution of any mode.Furthermore, we assume that every subset of tasksτ j,￿ (∀j, ￿) is EDF-schedulable.Open problem: For any given transition phase, what isthe earliest time-instant after the MCR at which all thenew mode tasks can be safely activated?Observation 1. In order to preserve the schedulabilityof the system, it might be the case that some MI taskshave to migrate from one processor to another when aτ1 τ2 τ3 τ4 τ5 τ6Ci 20 14 20 30 1 6Ti 39.2 30 60 60 10 10Ui 0.51 0.46 0.4 0.5 0.1 0.6belongs to τ1 MI MI MI τ1 τ2Table I: A task set to illustrate the necessity of task migrationacross different modes.τ2τ2τ3 τ3τ4τ2Y1 = 50Y2 = 51τ3 τ3MCRΠ2Π10521 30 t90τ1τ1τ2 τ2τ4τ2τ4Figure 2: Schedule missing deadline with uniprocessor protocoladaptationmode transition is initiated.Consider a system with two modes M1 and M2, andsix tasks {τ1, . . . , τ6}. These tasks have to be scheduledon two processors π1 and π2, and their parameters aregiven in Table 1. The notation MI indicates that thetask belongs to both modes M1 and M2. Thus we haveτ1 = {τ1, τ2, τ3, τ4, τ5} and τ2 = {τ2, τ3, τ4, τ6}. It canbe shown that the only EDF-schedulable partitions forτ1 is {{τ1, τ2}, {τ3, τ4, τ5}}. Similarly, the only EDF-schedulable partitions for τ2 is {{τ2, τ4}, {τ3, τ6}}. Thatis, there is no EDF-schedulable partitions in which everyMI task is assigned to the same processor in both modesM1 and M2, hence providing Observation 1.Observation 2. While it is commonly believed that unipro-cessor scheduling techniques can be directly applied topartitioned multi-core scheduling, the presence of MI tasksmay lead to counter-intuitive results.Consider the following uniprocessor result [1]: for anytransition phase from mode Mi to mode Mj , the new-mode tasks can be safely activated at any time t ≥ tMCR+Yi,j , where tMCR is the time-instant of the last MCR andYi,jdef=￿τ￿∈τ i C￿ +￿τ￿∈τ i∩τj￿Yi,jT￿￿× C￿. A directadaptation of the above protocol to partitioned multi-corewould be: for any transition phase from mode Mi to modeMj , the new-mode tasks can be safely activated at anytime t ≥ tMCR + maxmk=1￿Y ki,j￿, where tMCR is theτ1τ2τ2 τ2 τ2τ2τ4τ3 τ3τ4Y1 = 50Y2 = 51τ2 τ2τ3τ4MCRΠ2Π10521 30 tFigure 1: schedule of the two partitions with mode transition prolongedinstant of the last MCR andY ki,jdef=￿τ￿∈τ i,kC￿ +￿τ￿∈τ i,k∩τj,k￿Y ki,jT￿￿× C￿.However, the example using the system described inFigure 1 proves that this straight-forward extension of theprotocol lead to deadline miss. In Figure 2 a deadline ismissed at time t = 90 after the assumed end of the modetransition phase which completes at t = 52 since tMCR =1 and maxmk=1￿Y ki,j￿= 51. It thus shows that waiting forthe old mode workload to finish in every cores is not asufficient condition to command the mode transition.Observation 3. There exist time intervals in which modetransition can be performed without missing any deadlinesin the system. These intervals are separated by timeintervals in which mode transition cannot be performedwithout missing a deadline.The extended schedule of the system discussed inObservation 1 is shown in Figure 1. We can observe fromthe schedule that the time intervals where it is safe toperform mode transition and time intervals where it isnot safe to perform mode transition alternate. Hence, itis difficult to find at design time a time instant (using auniprocessor multimode protocol) at which it is alwayssafe to perform mode transition (as MCR is a run-timeevent).Hence, from Observations 2 and 3, we can concludethat the uniprocessor multimode scheduling techniquescannot be directly applied to a multiprocessor multimodepartitioned scheduling scenario.ACKNOLEDGEMENTSThis work was supported by the RePoMuC project, ref. FCOMP-01-0124-FEDER-015050, funded by FEDER funds through COMPETE(POFC - Operational Programme Thematic Factors of Competitiveness)and by National Funds (PT) through FCT - Portuguese Foundationfor Science and Technology and the RECOMP the project, funded byNational Funds, through the FCT, under grant ref.- ARTEMIS/0202/2009, as well as by the ARTEMIS Joint Undertaking, under grant agreementGrant nr. 100202.REFERENCES[1] Jorge Real, Alfons Crespo: Mode Change Protocols forReal-Time Systems: A Survey and a New Proposal. Real-Time Systems 26(2): 161–197 (2004).

Partitioned scheduling of multimode systems on multiprocessor platforms: when to do the mode transition?

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Partitioned scheduling of multimode systems on multiprocessor platforms: when to do the mode transition?

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