Reference Model of Real-Time Systems

1. Functional Parameter &Scheduling
Hierarchy
BY
Aananda Bhandari
Shubham Ghimire
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2. Functonal Parameter
• Preemptivity Of Jobs
• Criticality Of Jobs
• Optional Execution
• Laxity Type And Laxity Function
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3. Preemptivity Of Jobs
• Preemptable Job :- Can be suspended and
resumed from the suspention point
• Example :- Computations
• Non-preemptable :- Data transmission
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4. Criticality Of Jobs
• Criticality of job :- Positive number indicating
how critical the job is.
• Increases with importance of job
• Don’t use the terms priority and weight
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5. Optional Executions
• If an optional job or optional portion
completes late or is not executed at all, the
system still functions satisfactorily.
• Non-optional job :- Mandatory
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6. Laxity Type & Laxity Functions
• Laxity type:- indicates whether the job is hard
or soft.
• Hard RT Jobs:- “Better never than late”.
• Soft RT Jobs:- Usefulness decreases gradually.
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7. Resource Parameters Of Jobs &
Parameters Of Job Resources
• Preemptivity Of Resources
• Resource Graph
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8. Preemptivity Of Resources
• Describing processors and resources
independently of application Parameter of
resources: Preemptivity.
• Nonpreemptable resource: Each unit is to be
used serially.
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9. Resource Graph
• Configuration of the resources
• Vertex Ri for every processor or resource Ri in
the system.
• Attributes of the vertex are the parameters of
the resource.
• P- processors, R- for passive resources
• Parameters
– Type
– Number of available units.
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10. Scheduling Hierrarchy
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11. Scheduling Hierarchy
• Task Graph
– Representation of application system.
– Processor time
– Resource requirement
– Timing constraints & dependencies of jobs
• Resource Graph
– Amount of available resources
– Resource attributes
– Usage rules
• Scheduling and resource access-control
algorithms used by the operating system.
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12. Scheduler & Schedules
• Scheduler:
– implements scheduling algorithms
–Schedules Jobs,
–Allocates Resources.
Example: Processors assignment on jobs (or vice
versa).
• Schedule: Assignment of all system jobs on
available processors produced by the scheduler.
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13. Valid Schedule
• Every processor assigned to at most one job at
any time
• Every job is assigned at most one processor at
any time.
• No job is scheduled before its release-time.
• Total amount of processor time = execution
time
• Precedence and resource usage constraints
are satisfied.
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14. Feasibility, Optimality & Performance
Measures
• valid schedule is a feasible schedule if every
job completes by its deadline.
• Hard RTS scheduling algorithm is optimal if
(using) the algorithm (the scheduler) always
produces a feasible schedule if the given set of
jobs has feasible schedules.
• Lateness, tardiness, miss ,loss and invalid
rates.
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15. Thank You
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Reference : Real-Time Systems , Jane W. S. Liu