Fault Tolerant Scheduling of Mixed Criticality Real-Time Tasks under Error Bursts Abhilash Thekkilakattil, Radu Dobrin and Sasikumar Punnekkat

Real-time tasks Dependable Hard Real-time Systems web images Mixed-criticality requirements Fault tolerance requirements Timing requirements

job1job2 Worst Case Execution Time Inter-arrival time (Period) Release time Real-time scheduling: find a schedule for any given taskset that guarantees all tasks’ completion before the deadline Relative deadline

Real-time tasks Dependable Hard Real-time Systems web images Mixed-criticality requirements Fault tolerance requirements Timing requirements

Fault Tolerance Requirements Temporal redundancy Fault tolerance related overhead Fault: Hypothesized cause of an error that may lead to a failure Spatial redundancy replica 1 replica 2 voter Our focus

The Error Burst Model Increasing variety of error sources ●Electromagnetic interference from ubiquitous devices e.g., cellphones, radars and radio sets … having new characteristics ●Occurs continuously over a period of time: error bursts classical error model (errors as singleton events) extended error model (errors as bursts of events)

Real-time tasks Dependable Hard Real-time Systems web images Mixed-criticality requirements Fault tolerance requirements Timing requirements

Mixed Criticalities Critical (Flight critical functionalities) Non-critical (Inflight entertainment) Normal operation Abnormal operation discard Taken from toonpool.com

System Model 1.Set of real-time tasks 1.Two levels of criticalities 2.Known error burst length critical non-critical error burst

Problem Statement How can we guarantee: 1.All critical tasks meet their deadlines under error bursts 2.All non-critical tasks meet their deadlines if they are not hit by error bursts

Overview of the Solution Work generated in any time interval ≤ size of the interval. Case 1 : If no critical job is hit by the error burst Case 2 : When the error burst hits only a single critical job Case 3 : When the error burst hits more than one critical jobs

Conclusions We propose a schedulability analysis for EDF scheduled mixed criticality real-time systems under error bursts Enables the use of “normal” EDF scheduler for mixed criticality scheduling Use of existing operating systems e.g., ERIKA No commercial operating system support for mixed criticality scheduling Future work: Exploit the use of frequency scaling to control transient overloads

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