An on line approach to reduce delay variations on real time operating systems
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An On-line Approach to Reduce Delay Variations on Real-Time Operating Systems. Shengyan Hong. Problem. Reduce Delay Variations of Tasks. Why Important?. Delay Variations degrade hardware performance, e.g. sluggish response, erroneous behavior. Task Model.

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Problem
Problem Operating Systems

  • Reduce Delay Variations of Tasks


Why important
Why Important? Operating Systems

  • Delay Variations degrade hardware performance, e.g. sluggish response, erroneous behavior.


Task model
Task Model Operating Systems

  • Original Task Model (Ci, Di, Pi)

  • IMF Task Model

    • initial subtask (Cii, Dii, Pi, Oii=0)

    • mandatory subtask (Cim, Dim, Pi, Oim=0)

    • final subtask (Cif, Dif, Pi, Oif)

  • ADR Task Model

    • initial subtask (Cii, Diinew, Piinew=Pi/Mi)

    • mandatory subtask (Cimnew, Dimnew, Pi)

  • C* represents execution time, D* represents deadline, P* represents period, O* represents release time.


A trick in problem
A Trick in Problem Operating Systems

  • Suppose we have a task in original model, how to split mandatory subtask in IMF model to form ADR model?

    • Example, a task (Ci=5000,Di=27000,Pi=27000), and Cii and Cif consumes 10% of Ci,

    • The optimal scheme is to cut 8 splits from the mandatory subtask in IMF model.

The constraints (1), (2) and (3) help us get it.

(1)

(2)

(3)


Quadratic programming problem
Quadratic Programming Problem Operating Systems

Objective Function:

(4)

,where each term is an approximation of

.

(5)

Schedulability Constraint

or

Constraints (5), (6), (7) guarantees the correct running of Real-Time Operating Systems.

(6)

Deadline Constraints

(7)


Adr algorithm flow
ADR Algorithm Flow Operating Systems

Adjust deadlines of mandatory subtasks, and search a new solution, and the process is repeated until the algorithm converges.

Search an initial

feasible solution

with optimal model transformation.

For any fixed deadlines of mandatory subtasks,

compute an updated feasible solution, i.e. deadlines of initial subtasks.


Initial results
Initial Results Operating Systems

  • A custom simulator by C running on Linux

  • A task set with first two tasks decomposable

  • Compare results with original Delay Variations, and two representative methods

    • The smaller DV, the better the method is.

    • When workload changes, see which method can adapt to it.


The road ahead
The Road Ahead Operating Systems

  • If initial subtask and final subtask do not have the same execution time, what to do?

  • If mandatory subtask can not be divided, what to do?

  • Test more task sets in the simulator.

  • Show the performance of the proposed approach and the existing methods.


Questions? Operating Systems


Second trick in problem
Second Trick in Problem Operating Systems

  • Deadline constraints (6) and (7) incorporate the subtask dependencies to schedulability test without being overly pessimistic.

  • From (6), we can derive another constraint for Mi .

(6)

(7)

(8)


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