Towards a Fault-tolerant, Scheduling Methodology for Safety-critical Certified Information Systems

Today, many critical information systems have safety-critical and non-safety-critical functions executed on the same platform in order to reduce design and implementation costs. The set of safety-critical functionality is subject to certification requirements and the rest of the functionality does not need to be certified, or is certified to a lower level. The resulting mixed-criticality systems bring challenges in designing such systems, especially when the critical tasks are required to complete with a timing constraint. This paper studies a problem of scheduling a mixed-criticality system with fault tolerance. A fault-recovery technique called checkpointing is used where a program can go back to a recent checkpoint for re-execution upon errors occurred. A novel schedulability test is derived to ensure that the safety-critical tasks are completed before their deadlines and the theoretical correctness is shown

최신 ECU보드를 활용하여 소프트에러들을 실시간 복구하는 기법

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 컴퓨터공학부, 2020. 8. 이창건.This dissertation presents the fault-tolerant real-time scheduling using dynamic mode switch support of modern ECU hardware. This dissertation first describes the optimal capacity of the Periodic Resource which contains harmonic periodic task set using the exact time supply function.We show that the optimal capacity can be represented as sum of the each individual utilization of the task in the harmonic periodic task set for both normal state(i.e. no faults) and faulty state. Then, this dissertation proposes non-critical task overlapping technique by only using the idle time intervals of the Periodic Resource in order to overlap the non-critical tasks which ensures no additional capacity increase. Finally, this dissertation proposes the basic form of the Periodic Resources in order to efficiently use the dynamic mode switch support. Next, we also proposes the bin-packing heuristic algorithm that considers both making sub-taskset as a one Periodic Resource and Periodic Resource wide bin-packing which has the pseudo-polynomial time complexity. Experimental results show that the proposed algorithm performs better than the traditional partitioned fixed-priority scheduling approach and partitioned mixed-criticality scheduling approach. Also, the achievement is made up to 18% in terms of the total needed cores compared to traditional partitioned fixed-priority approach for making the given input task set schedulable.본 논문에서는 효율적인 재구성가능 시스템 사용을 위한 계층기반 실시간 결함 감내 스케줄링 기법을 제안한다. 본 연구는 주기 자원 모델을 기반으로, 최적 주기 자원 서버의 용량을 주기 자원 모델이 가지는 실시간 주기 태스크 셋의 유틸라이제이션의 합으로 제시한다. 본 논문은 해당 최적 서버 용량을 시스템이 정상 동작할때와 오동작 할때 모두에 대해서 제시한다. 다음으로, 비중요 태스크 셋들을 중요 주기 자원 서버의 여분 공백 시간을 활용해 서버 용량의 증가 없이 비중요 태스크를 중요 주기 자원 서버에 할당하는 방법론을 제시한다. 마지막으로 본 논문은 주기 자원 서버 단위의 파티션 기법과 주기 태스크를 하나의 주기 자원 서버로 만드는 빈패킹 휴리스틱 알고리즘을 제시한다. 실험 결과, 본 논문에서 제시한 알고리즘은 기존에 사용되었던 파티션 기반 우선순위 스케줄링 알고리즘과 파티션 기반 우선순위 혼잡 중요도 알고리즘보다 더 작은 수의 코어의 개수를 도출 할 수 있음을 보인다. 실험결과를 기반으로, 본 연구에서 제안한 알고리즘을 재구성가능 시스템에 활용한다면 기존 방법 대비 최대 18%의 코어절감효과를 기대할수 있다.1 Introduction 1 1.1 Motivation and Objective 1 1.2 Approach 2 1.3 Organization 6 2 System Model 7 3 Schedulability Analysis 10 3.1 Background 10 3.2 Optimal Capacity Analysis During Normal State 14 3.3 Optimal Capacity Analysis During Fault State 16 3.4 Periodic Resource Wide Schedulability Test 20 3.5 Non-Critical Task Overlapping 24 4 Proposed Approach 26 4.1 Minimum Harmonic Partitions of the Task Set 26 4.2 Proposed Heuristic Algorithm 28 4.2.1 Choosing Detection method 28 4.2.2 Packing Minimum Harmonic Partitions 29 4.2.3 Packing Free Tasks 30 4.2.4 Packing Non-Critical Tasks 31 4.3 Algorithm Description 32 5 Evaluation 35 5.1 Experimental Setup 35 5.2 Simulation Results 36 5.2.1 Free Task Bin-Packing 38 5.2.2 Minimum Harmonic Partitions Bin-Packing 40 5.2.3 Effect of Non-Critical Task Overlapping 43 5.2.4 Effect of State-Wise Computation 45 6 Related Works 46 6.1 Hierarchical Fault-Tolerant Real-Time Scheduling 46 6.2 Error Detection Method 46 7 Conclusion 48 References 50Maste

A Survey of Research into Mixed Criticality Systems

This survey covers research into mixed criticality systems that has been published since Vestal’s seminal paper in 2007, up until the end of 2016. The survey is organised along the lines of the major research areas within this topic. These include single processor analysis (including fixed priority and EDF scheduling, shared resources and static and synchronous scheduling), multiprocessor analysis, realistic models, and systems issues. The survey also explores the relationship between research into mixed criticality systems and other topics such as hard and soft time constraints, fault tolerant scheduling, hierarchical scheduling, cyber physical systems, probabilistic real-time systems, and industrial safety standards