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Fault Tolerant Scheduling of Mixed Criticality Real-Time Tasks under Error Bursts
Abhilash Thekkilakattil, Radu Dobrin and Sasikumar Punnekkat
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Real-time tasks
Dependable Hard Real-time Systems
web images
Mixed-criticalityrequirements
Fault tolerance requirements
Timing requirements
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Timing requirements
job1 job2
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
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Real-time tasks
Dependable Hard Real-time Systems
web images
Mixed-criticalityrequirements
Fault tolerance requirements
Timing requirements
![Page 5: Fault Tolerant Scheduling of Mixed Criticality Real-Time Tasks under Error Bursts Abhilash Thekkilakattil, Radu Dobrin and Sasikumar Punnekkat](https://reader033.vdocument.in/reader033/viewer/2022051621/5697bfbc1a28abf838ca1a96/html5/thumbnails/5.jpg)
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
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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)
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Real-time tasks
Dependable Hard Real-time Systems
web images
Mixed-criticalityrequirements
Fault tolerance requirements
Timing requirements
![Page 8: Fault Tolerant Scheduling of Mixed Criticality Real-Time Tasks under Error Bursts Abhilash Thekkilakattil, Radu Dobrin and Sasikumar Punnekkat](https://reader033.vdocument.in/reader033/viewer/2022051621/5697bfbc1a28abf838ca1a96/html5/thumbnails/8.jpg)
Mixed Criticalities
Critical(Flight critical functionalities)
Non-critical(Inflight entertainment)
Normal operationAbnormal operation
discard
Taken from toonpool.com
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System Model
1. Set of real-time tasks
2. Two levels of criticalities
3. Known error burst length
critical
non-critical
error burst
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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
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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
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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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Thank you !
Questions ?