Adaptive Mid-term and Short-term Scheduling of Mixed-criticality Systems

A mixed-criticality real-time system is a real-time system having multiple tasks classified according to their criticality. Research on mixed-criticality systems started to provide an effective and cost efficient a priori verification process for safety critical systems. The higher the criticality of a task within a system and the more the system should guarantee the required level of service for it. However, such model poses new challenges with respect to scheduling and fault tolerance within real-time systems. Currently, mixed-criticality scheduling protocols severely degrade lower criticality tasks in case of resource shortage to provide the required level of service for the most critical ones. The actual research challenge in this field is to devise robust scheduling protocols to minimise the impact on less critical tasks. This dissertation introduces two approaches, one short-term and the other medium-term, to appropriately allocate computing resources to tasks within mixed-criticality systems both on uniprocessor and multiprocessor systems. The short-term strategy consists of a protocol named Lazy Bailout Protocol (LBP) to schedule mixed-criticality task sets on single core architectures. Scheduling decisions are made about tasks that are active in the ready queue and that have to be dispatched to the CPU. LBP minimises the service degradation for lower criticality tasks by providing to them a background execution during the system idle time. After, I refined LBP with variants that aim to further increase the service level provided for lower criticality tasks. However, this is achieved at an increased cost of either system offline analysis or complexity at runtime. The second approach, named Adaptive Tolerance-based Mixed-criticality Protocol (ATMP), decides at runtime which task has to be allocated to the active cores according to the available resources. ATMP permits to optimise the overall system utility by tuning the system workload in case of shortage of computing capacity at runtime. Unlike the majority of current mixed-criticality approaches, ATMP allows to smoothly degrade also higher criticality tasks to keep allocated lower criticality ones

ATMP: An Adaptive Tolerance-based Mixed-criticality Protocol for Multi-core Systems

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted ncomponent of this work in other works.The challenge of mixed-criticality scheduling is to keep tasks of higher criticality running in case of resource shortages caused by faults. Traditionally, mixedcriticality scheduling has focused on methods to handle faults where tasks overrun their optimistic worst-case execution time (WCET) estimate. In this paper we present the Adaptive Tolerance based Mixed-criticality Protocol (ATMP), which generalises the concept of mixed-criticality scheduling to handle also faults of other nature, like failure of cores in a multi-core system. ATMP is an adaptation method triggered by resource shortage at runtime. The first step of ATMP is to re-partition the task to the available cores and the second step is to optimise the utility at each core using the tolerance-based real-time computing model (TRTCM). The evaluation shows that the utility optimisation of ATMP can achieve a smoother degradation of service compared to just abandoning tasks

ODRE Workshop: Using SIL Arithmetic to Design Safe and Secure Systems

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In a safety-critical system each service has a specific level of safety criticality. Safety standards use classifications like Safety Integrity Levels (SIL), to describe the design requirements for the individual services of a system. Techniques like redundancy can be used to achieve a higher overall dependability than the used individual components provide. Using the notion of SIL, this can be called SIL arithmetic. In this paper we describe the concept of SIL arithmetic and point out how different safety standards provide hints for their support of using SIL arithmetic. We highlight the principal benefits of SIL arithmetic and provide simple examples. But the use of SIL arithmetic in a concrete system design can also have its pitfalls, which we also discuss in this paper. We specifically discuss these issues in the context of scheduling techniques for mixed-criticality systems, where resource shortages are to be handled by the scheduler

Optimised Adaptation of Mixed-criticality Systems with Periodic Tasks on Uniform Multiprocessors in Case of Faults

Raimund Kirner, Saverio Iacovelli and Michael Zolda, 'Optimised Adaptation of Mixed-criticality Systems with Periodic Tasks on Uniform Multiprocessors in Case of Faults' paper presented at the IEEE Workshop on Software Technologies for Future Embedded and Ubiquitous Systems (SEUS'15) Auckland, New Zealand. 13-17 April 2015.The standard real-time computing model is based on a notion of deadline that represents both, a design parameter and a critical latency. The tolerance-based real-time com- puting model (TRTCM) extends the standard real-time com- puting model to reflect good engineering practice, where a safety margin is added to the critical latency to obtain the corresponding design parameter. The key feature of TRTCM is to add a tolerance range, which in combination with criticality specifications for services allows for fault- tolerant mixed-criticality scheduling with smooth degrada- tion of service utility in case of resource shortage. In this paper we study the applicability of TRTCM for periodic tasks with mixed criticality on uniform multipro- cessor systems. To optimise the system adaptation in case of resource shortage we formulate utility maximisation based on TRTCM as an optimisation problem. We describe two implementation strategies and derive an optimisation prob- lem to be solved by a constraint solver for each. We use a video processing application for a concrete evaluation. Our results show that TRTCM can provide better utility than standard mixed-criticality approaches where lower critical- ity services are skipped in case of resource shortage

Symptoms-to-emergency-call timing delay in acute coronary syndrome before and during COVID-19: independent predictors and their impact on mortality

The COVID-19 pandemic severely impacted global health. The aim of this study was to compare predictors of symptoms-to-emergency-call timing delay in Acute Coronary Syndrome (ACS) and their impact on mortality before and during the COVID-19 outbreak

The Incidence and Impact of In-Hospital Bleeding in Patients with Acute Coronary Syndrome during the COVID-19 Pandemic

Background: The COVID-19 pandemic increased the complexity of the clinical management and pharmacological treatment of patients presenting with an Acute Coronary Syndrome (ACS). Aim: to explore the incidence and prognostic impact of in-hospital bleeding in patients presenting with ACS before and during the COVID-19 pandemic. Methods: We evaluated in-hospital Thrombolysis In Myocardial Infarction (TIMI) major and minor bleeding among 2851 patients with ACS from 17 Italian centers during the first wave of the COVID-19 pandemic (i.e., March-April 2020) and in the same period in the previous two years. Results: The incidence of in-hospital TIMI major and minor bleeding was similar before and during the COVID-19 pandemic. TIMI major or minor bleeding was associated with a significant threefold increase in all-cause mortality, with a similar prognostic impact before and during the COVID-19 pandemic. Conclusions: the incidence and clinical impact of in-hospital bleeding in ACS patients was similar before and during the COVID-19 pandemic. We confirmed a significant and sizable negative prognostic impact of in-hospital bleeding in ACS patients