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Dynamic Scheduling Hard Real-Time Applications in Open System Environment

Dynamic Scheduling Hard Real-Time Applications in Open System Environment. Z. Deng J.W.-S. Liu J. Sun Department of Computer Science University of Illinois at Urbana-Champaign Urbana, IL 61801 October 22, 1996

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Dynamic Scheduling Hard Real-Time Applications in Open System Environment

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  1. Dynamic Scheduling Hard Real-Time Applications in Open System Environment Z. Deng J.W.-S. Liu J. Sun Department of Computer Science University of Illinois at Urbana-Champaign Urbana, IL 61801 October 22, 1996 Presenter : Shu Wei Ho

  2. Outline • Motivation • Environment • Schedulability Condition of Sporadic Jobs With EDF Algorithm • Schedulability Condition of Real-Time Applications • Scheduling Algorithm for Real-Time Applications in Open System • Conclusion

  3. Motivation • Schedule applications with one processor. • Make sure all applications accuracy.

  4. Motivation • Purpose - Validate - Easy test - Non-real time response - Without fixed allocation

  5. Environment 排程圖

  6. Environment • Two level scheduling • Top level - OS scheduler(EDF) • Low level - Server scheduler

  7. Schedulability Condition of Sporadic Jobs With EDF Algorithm • Execution time equalto the server budget and deadline equal to the server deadline. • Execution time(ei) and deadline(d) are known when application arrives. Theorem A system of independent, preemptable sporadic jobs is schedulable accordingto the EDF algorithm if at any time instant, the total density of all active jobs in the system isless than or equal to 1 .

  8. Schedulability Condition of Sporadic Jobs With EDF Algorithm Corollary In a system of a varying number of independent, preemptable periodic taskswhose deadlines are equal to their respective periods and a varying number of constant utilization servers, if the total utilization Utotal of all the periodic tasks and the total server size Us of all the servers are such that Utotal + Us ≤ 1 at all times, then all periodic tasks and all servers are schedulable according to the EDF algorithm.

  9. Schedulability Condition of Real-Time Applications Task ( arrive(rn) , execution , deadline (dn))(t) J1 ( 0 , a , 10a+4 ) J2 ( a , 1 , a+4 ) J2 : ( a+4-a)*0.25 = 1 J1 : ( 4a + 4)*0.25 – 1 = a a < 1 + 架構圖

  10. Schedulability Condition of Real-Time Applications

  11. Schedulability Condition of Real-Time Applications +

  12. Scheduling Algorithm for Real-Time Applications in Open System • Nonpreemptive • Sporadic When a new job Jiof Ak arrives at t with deadline d if test Utotal + σk≤1 -> d = t + ei ⁄ σk

  13. Scheduling Algorithm for Real-Time Applications in Open System • Preemptive • Periodic When a new task Ti of Ak arrives at ri with period pi, if test Uk + σk≤1, and the q-th job of task Ti will be scheduled at t with deadline d=Min(t + ei ⁄ σk, ri + (q-1)*pi)

  14. Scheduling Algorithm for Real-Time Applications in Open System • Hence if the application Ak is schedulable on the slow processor, no matter it is preemptive or not, is schedulable in the open system. • Utotal + σk≤1

  15. Conclusion • When it comes a new application Ak Non-real-time → accept Real-time → test Utotal + σk≤1 → success → set server budget → apply Utotal = Utotal + σk • When an application finish Utotal = Utotal - σk

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