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FALSE2002, Nashville, Nov. 14-15, 2002. Software D y namic s: A New Method of Evaluating Real-Time Performance of Distributed Systems. Janusz Zalewski Computer Science Florida Gulf Coast University Ft. Myers, FL 33965-6565 http://www.fgcu.edu/zalewski/.

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FALSE2002, Nashville, Nov. 14-15, 2002

Software Dynamics:

A New Method of Evaluating Real-Time

Performance of Distributed Systems

Janusz Zalewski

Computer Science

Florida Gulf Coast University

Ft. Myers, FL 33965-6565

http://www.fgcu.edu/zalewski/


FALSE2002, Nashville, Nov. 14-15, 2002

Talk Outline

  • RT Software Architecture

  • Evaluating S/W Architectures

  • Timeliness & S/W Dynamics

  • Conclusion



FALSE2002, Nashville, Nov. 14-15, 2002

Generic Real-Time

Software Architecture


FALSE2002, Nashville, Nov. 14-15, 2002

Basic Components of Real-TimeSoftware Architecture

  • Sensor/Actuator component

  • User Interface component

  • Communication Link component

  • Database component

  • Processing component

  • Timing component.


FALSE2002, Nashville, Nov. 14-15, 2002

Air-Traffic Control System

Physical Diagram


FALSE2002, Nashville, Nov. 14-15, 2002

Air-Traffic Control System

Context Diagram


FALSE2002, Nashville, Nov. 14-15, 2002

The idea of grouping I/O information into different categories, which later determine the software architecture follows the fundamental software engineering principle of separation of concerns (Parnas, 1970s).


FALSE2002, Nashville, Nov. 14-15, 2002

Model of a Distributed

Embedded Simulation


FALSE2002, Nashville, Nov. 14-15, 2002

We are missing good (any) measures to characterize Behavioral Properties of a software module (its dynamics).


FALSE2002, Nashville, Nov. 14-15, 2002

Interrupt Latency

The time interval between the occurrence of an external event and start of the first instruction of the interrupt service routine.


FALSE2002, Nashville, Nov. 14-15, 2002

Interrupt Latency Involves

  • H/W logic processing

  • Interrupt disable time

  • Handling higher H/W priorities

  • Switching to handler code.


FALSE2002, Nashville, Nov. 14-15, 2002

Real-Time System

Responsiveness


FALSE2002, Nashville, Nov. 14-15, 2002

Dispatch Latency

The time interval between the end of the interrupt handler code and the first instruction of the process activated (made runnable) by this interrupt.


FALSE2002, Nashville, Nov. 14-15, 2002

Dispatch Latency Involves

  • OS decision time to reschedule (non-preemptive kernel state)

  • context switch time

  • return from OS call.


FALSE2002, Nashville, Nov. 14-15, 2002

Real-Time Properties

* Responsiveness

* Timeliness

* Schedulability

* Predictability


FALSE2002, Nashville, Nov. 14-15, 2002

How to measure these properties?* Responsiveness - just outlined* Timeliness - proposed below* Schedulability - rate monotonic and deadline monotonic analyses.


FALSE2002, Nashville, Nov. 14-15, 2002

Two measures of timeliness:* Overall time deadlines are missed (by a task)* Number of times deadlines are missed by X percent



FALSE2002, Nashville, Nov. 14-15, 2002

Overall time the deadlines are missed for 100 experiments.



FALSE2002, Nashville, Nov. 14-15, 2002

Overall time the deadlines are missed for 100 experiments (CORBA).


FALSE2002, Nashville, Nov. 14-15, 2002

The number of times the deadlines are missed by 2% (CORBA).


FALSE2002, Nashville, Nov. 14-15, 2002

ATCS: Software Components

Communicating via CORBA


FALSE2002, Nashville, Nov. 14-15, 2002

Overall time (in milliseconds) deadlines are missed for 20 aircraft (in 100 experiments).


FALSE2002, Nashville, Nov. 14-15, 2002

Number of times deadlines are missed by more than 20% for 20 aircraft (in 100 experiments).




FALSE2002, Nashville, Nov. 14-15, 2002

Satellite Ground Control Station



FALSE2002, Nashville, Nov. 14-15, 2002

SGCS Physical Architecture



FALSE2002, Nashville, Nov. 14-15, 2002

Single DB Client Request Processing Time.


FALSE2002, Nashville, Nov. 14-15, 2002

Percent of deadlines missed for one DB Client.


FALSE2002, Nashville, Nov. 14-15, 2002

Five DB Clients Request Processing Time.


FALSE2002, Nashville, Nov. 14-15, 2002

Percent of deadlines missed for five DB Clients.


FALSE2002, Nashville, Nov. 14-15, 2002

Sensitivity:a measure of the magnitude of system’s response to changes.


FALSE2002, Nashville, Nov. 14-15, 2002

Sensitivity:(y1 – y0)/[(y1 + y0)/2] (x1 – x0)/[(x1 + x0)/2]





FALSE2002, Nashville, Nov. 14-15, 2002

First Order Dynamics G(s) = K / (t*s + 1)


FALSE2002, Nashville, Nov. 14-15, 2002

Time constant - t:a measure of the speed of system’s response to changes.


FALSE2002, Nashville, Nov. 14-15, 2002

  • Settling Time:

  • time when curve reaches 2% max

  • Time Constant = 0.25 * Settling Time





FALSE2002, Nashville, Nov. 14-15, 2002

Distributed Embedded Simulation Architecture


FALSE2002, Nashville, Nov. 14-15, 2002

Statistical measures of timeliness: * Round-trip time stability * Service time effect


FALSE2002, Nashville, Nov. 14-15, 2002

Service time effect for a specific architecture


FALSE2002, Nashville, Nov. 14-15, 2002

Round-trip message time for 5-task simulation


FALSE2002, Nashville, Nov. 14-15, 2002

Conclusion

  • Behavioral Properties are crucial for successful software development

  • Sensitivity is one important property

  • Software Dynamics seems to be a measurable property as well


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