Fault Tolerant Scheduling of Mixed Criticality Real-Time Tasks
under Error Bursts
Abhilash Thekkilakattil, Radu Dobrin and Sasikumar Punnekkat
Dependable Hard Real-time Systems
Fault tolerance
requirements
Mixed-criticality
requirements
Timing requirements
Real-time
tasks
web images
Timing requirements
Worst Case Execution
Time
Relative
deadline
Release
time
job1
job2
Inter-arrival time (Period)
Real-time scheduling: find a schedule for any given taskset that
guarantees all tasks’ completion before the deadline
Dependable Hard Real-time Systems
Fault tolerance
requirements
Mixed-criticality
requirements
Timing requirements
Real-time
tasks
web images
Fault Tolerance Requirements
Fault: Hypothesized cause of an error that may lead to a failure
Our focus
Temporal redundancy
Spatial redundancy
replica 1
voter
Fault tolerance related overhead
replica 2
The Error Burst Model
classical error model
(errors as singleton events)
extended error model
(errors as bursts of events)
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
Dependable Hard Real-time Systems
Fault tolerance
requirements
Mixed-criticality
requirements
Timing requirements
Real-time
tasks
web images
Mixed Criticalities
Taken from toonpool.com
Abnormal operation
Normal operation
Critical
(Flight critical functionalities)
Non-critical
(Inflight entertainment)
discard
System Model
error burst
1.
Set of real-time tasks
critical
1.
Two levels of criticalities
2.
Known error burst length
non-critical
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
Case 1 : If no critical job is hit by the error burst
Work generated in any
time interval ≤ size of the
interval.
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
Thank you !
Questions ?