Eddie JesinskyNASA/WVU ATL Internejesinsk@mix.wvu.edu

An Introduction To

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Overview NASA/WVU Applied Technology Lab

Tri-Pacific Software

What is it?

Rate Monotonic Scheduling

Rate Monotonic Analysis

RapidRMA Background

Tutorial

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RapidRMA Overview Use

Benefits

Features

Capabilities

Requirements

Cost

Maturity

Installation

Tutorial

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Applied Technology Lab

Established: 2007

Partnership between WVU and NASA's Independent Verification and Validation (IV&V) facility in Fairmont, WV

Research software engineering technologies that improve and enhance the way NASA produces safe and reliable system software.

http://atl.wvu.edu

Director:

Dr. Tim Menzies, Ph.D.

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Tri-Pacific Software Founded in 1984 to provide consulting, customized training, and

software development services

Chosen by the Software Engineering Institute (SEI) to be in a technology exchange to bring Rate Monotonic Analysis to industry

Worked with the University of Illinois at Champaign-Urbana to incorporate their RMA research into a commercially available tool called PERTS- Prototyping Environment for Real-Time Systems – now RapidRMA

Founded by Peter Kortmann, President, and Fred Kortmann, CFO

http://www.tripac.com

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What is it? Allows real-time systems software developers to prevent costly

design mistakes and accelerate their development schedules

Allows users to study the effects and relationships of various parameters in the system that directly affect the schedulability of the entire task set

Multiple analysis tools allow designers to test software models against various design scenarios and evaluate how different implementations can optimize performance

Implements object oriented resource contention protocol, Distributed Affected Set Priority Ceiling Protocol (DASPCP), developed by University of Rhode Island and SPAWAR

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Rate Monotonic Scheduling Preemptive

Interrupts tasks and resumes them later As opposed to Cooperative – allows tasks to finish

Fixed Priority

Static: task period must be known in advance Rate Monotonic Prioritization

Shorter the period, higher the priority Other solutions: Deadline Monotonic – earliest deadline first

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Rate Monotonic Analysis Collection of quantitative methods and algorithms for predicting

whether a system will meet its timing and throughput requirements when it is operational

Guarantees that a system is schedulable with a set of given requirements

Requires that the total task utilization be less than or equal to the utilization bound

Total task utilization:

C1/T

1 + ...C

N/T

N

Utilization bound:

U(N) = N(21/N - 1)

- Ci = worst case task-execution time of each task i

- T i = period of each task i

- i ranges from 1 to N

Ref: Liu & Layland (1973)

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Rate Monotonic Analysis - 2

Example:

Task Characteristics:

Task Work PeriodA 5 20B 10 40C 12 60

Total Task Utilization:

5/20 + 10/40 + 12/60 = 0.25 + 0.25 + 0.20 = .7 = 70%

Utilization Bound:

U(3) = 3(21/3 – 1) = 0.779 = 77.9%

Pessimistic – based on worst-case execution time of each task – guarantees schedulability

Tasks still may be schedulable if they exceed the utilization bound – response time test must be performed based on processor time demand

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RapidRMA Overview Use

Benefits

Features

Capabilities

Requirements

Cost

Maturity

Installation

Tutorial

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Use Problem commonly revealed as a result of RMA: priority

inversion

Execution of higher priority thread forced to wait for a lower priority thread to release a resource

Mars Pathfinder

Failure to enable protection against priority inversion Before launch testing limited to “best-case” high data

rates and science activities RapidRMA performs “worst-case” schedulability analysis

Could have been caught in testing

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Benefits Allows cost effective testing and modeling of systems

Guarantees schedulability under “worst case” conditions

Isolates and identifies timing problems

Provides “what if” support to identify bottlenecks and performance issues

Prevents users from performing unnecessary tasks

Recompiling and executing the software to see if a change worked

Moving functionality from a task to an interrupt service routine

Re-allocating resources that can be analyzed in the model before being implemented in the software

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Features Timing and scheduling analysis environment

Utilizes powerful Rate Monotonic Analysis methodology

Provides support for the following algorithms and analysis:

Rate Monotonic Deadline Monotonic Cyclic Executive ROSA Aperiodic Simulation

Interfaces for Ilogix Rhapsody and IBM/Rational Rose Real-Time RT-UML support, and Wind River's WindView

Support for Real-Time CORBA semantics

Also:

- Periodic task handling- Aperiodic job handling

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Capabilities RapidRMA is for:

Hard real-time systems – flight control, medical device Soft real-time systems – networks, telecommunications

Used:

During system design: to validate the timing requirements of a new system before coding

When prototyping: to identify potential architecture problems and revalidating timing requirements

On existing system: to pinpoint potential timing problems and bottlenecks in the architecture

Iteratively throughout the life of the system: will changes to the system alter the timing requirements?

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Capabilities - 2IV&V ATL

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RapidRMA Overview Use

Benefits

Features

Capabilities

Requirements

Cost

Maturity

Installation

Tutorial

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Requirements Windows 2000, XP, Solaris, Linux Java Run-Time Environment Short 1-2 day tutorial required for basic RMA

knowledge Can be incorporated into existing software

engineering processes with relative ease incrementally

Abstracting the system architecture takes a different type of thinking

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Cost RapidRMA Licensing (January 2008 Price List)

Node Locked License: $4995.00 per seat Floating License: $7995.00 per seat Node Locked License for RT UML: $6995.00 per seat Floating License for RT UML: $9995.00 per seat

Maintenance: 19% retail cost

Training: $4000 + expenses/day or $3500 each for 2

Consulting: $3250/day or $3000/day with 25 day block

Quick Start Program: $50,000 (20 days combined training and mentoring for first 2 months of project

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Maturity In 1989 IBM applied RMA to a sonar training system,

allowing them to discover and correct performance problems

Recommended by IBM Federal Sector Division (now Lockheed Martin) for its real-time products since 1990

RMA was applied successfully by the US Navy to an active and passive sonar of a major submarine system

RMA was adopted in 1990 by NASA for development of real-time software for the space station data management subsystem

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Installation Download the Java 1.6 runtime environment from

http://java.sun.com/javase/downloads/index.jsp Purchase a license key from license@tripac.com Download your version of RapidRMA from

http://tripac.com/html/downloads.html Install both the Java 1.6 runtime environment and

RapidRMA executables Cut and paste the license text you received into the

license.lic dummy file in the RapidRMA directory after it has been installed

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Tutorial Introduction RapidRMA has three major sections

Resource Editor Task Editor Schedulability Analyzer

The Resource Editor and Task Editor each have two views

Graph Editor Spreadsheet Editor

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Resource Graph Editor Define the

system resources to be used by the tasks in the Task Graph editor.

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Task Graph Editor Define the tasks

of the system to be modeled in the Task Graph Editor

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Schedulability Analyzer Use the

Schedulability Analyzer to analyze the model defined in the Task and Resource Graphs.

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Importing Data

You can skip the defining of resources and tasks by using the Import interface.

Perts Models Import Previous PERTS

models into RapidRMA form

WindView Users Directly import from WindView

2 log file

ObjecTime Users Directly import a Developer

linear form model

Select the linear form files generated by Developer 5.2

Illuminator Users Directly import from an

Illuminator log file

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Defining the Resources

1) Add root nodes and child resources2) Define the parameters of each resource

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Defining the Resources

3) Show any resource accesses across nodes and DASPCPconflicting nodes

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Defining the Tasks

1) Use the Task Graph Editor to define tasks

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Defining the Tasks

2) Specify the parameters of each task: Period, Amount of Work,Relative Deadline, Active Resource

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Required Task Parameters Period

Can be either periodic (Deterministic) or aperiodic (Uniform, Exponential, or Histogram)

Amount of Work Can be either periodic (Deterministic) or aperiodic (Uniform, Exponential,

or Histogram)

Relative Deadline The point in time relative to the ready event by which the response must

be complete for the timing behavior of the response to be correct

Active Resource The name of the node and CPU that the task will run on in the form

NodeName.CPU (Resource ID)

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Specify Task Parameters

The Add Resource Dialog Allows you to add,

remove, and change the resources used by a task

When you specify that a task uses a resource, you must specify the time intervals in which it is used

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Specify Task Parameters

A task may require one or more resources. Each resource requirement for a task has a start

and finish time. A resource requirement can involve multiple

numbers of the resource.

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Show Task Dependencies

Show any dependencies between tasks. End-To-End Analysis is not possible unless

dependencies are defined.

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Aperiodic Tasks RapidRMA bind aperiodic tasks to periodic

servers RapidRMA assigns each aperiodic task to

a unique periodic server within a node During Single-Node Analysis or from the

Task Graph Editor, you can reassign aperiodic tasks to different servers

You can select among various types of periodic servers (sporadic, polling, etc)

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Define Intermediate Deadlines

To model a CORBA system, each client is automatically segmented into a sequence of dependent tasks.

Use intermediate deadlines to define where the client accesses CORBA services.

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Run Schedulability Analysis

Specify the analysis type Specify the algorithm and priority assignment

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Select Analysis Type

Single-Node Analysis Show the schedulability of tasks and resources assigned

to a single node, and provides powerful what-if modeling tools

Multiple-Node Analysis Allows the assignment of tasks to nodes, partitions

resources among nodes, and shows the schedulability results of a complete multiprocessor system

End-To-End Analysis Shows whether each task can always meet its deadlines,

providing worst-case completion times

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Single Node Analysis

Shows details about the selected node. Data about each task is included.

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Multiple Node Analysis

With Auto Binding, only schedulable tasks are assigned to nodes.

You can use one of 4 algorithms for Auto Binding:

First Fit: Each task is assigned to the first node where schedulability is guaranteed

Best Fit: Each task is assigned to the node which may result in the least amount of blocking

Next Fit: As many tasks as possible are assigned to each node in turn

Worst Fit: Each task is assigned to the node which may result in the greatest amount of blocking

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End To End Analysis End-To-End Scheduling looks at the schedulability

of a system with one or more paths of execution defined by a series of dependencies between tasks.

The worst-case completion time is given on each node.

Single-Node Analysis can also be performed on each node.

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Time Demand Analysis

Time Demand Analysis shows the graph of time demand vs time supply

Both schedulable and non-schedulable tasks are shown

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Processor Utilization Analysis

The Utilization dialogue shows the selected task, higher tasks, and any blocking

Details are available by clicking the appropriate button

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Blocking Analysis

Blocking details include information about each blocking occurrence

You can see the next, previous and worst blocking conditions

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What-If Analysis

RapidRMA allows you to do “what-if” analysis on individual tasks

RapidRMA can also propose changes to make the task schedulable

A change in execution time from 40 to 36 will make this task schedulable.

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What-If Analysis

In this example, a change in processing rate for Node_1 to 1.25 (from a base of 1.00) makes this

model schedulable.

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Schedules

You can see a timeline of the schedules for any resources and tasks on a selected node.

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Periodic Server Analysis The Task Graph Editor

shows the periodic servers created by the Schedulability Analyzer

The Aperiodic Task menu lets you review and alter attributes and aperiodic tasks and their periodic servers

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Aperiodic Simulation

The Aperiodic Simulation window lists the servers on the node, the tasks for the chosen server, a choice of complexity levels, and user-definable server parameters

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Resources RapidRMA

http://www.tripac.com/html/prod-fact-rrm.html http://www.tripac.com/html/tech-bkgd-rma.html http://tripac.com/html/downloads.html (RapidRMA

tutorial) http://www.nasa.gov/centers/ivv/doc/207836main_RRMA-RAPIDRMA-WebEval.doc

Rate Monotonic Analysis

http://www.sei.cmu.edu/str/descriptions/rma_body.html http://ece.cmu.edu/~koopman/des_s99/real_time/ http://www.edn.com/archives/1997/090197/18df_03.htm

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QUESTIONS?

Thank you

Eddie Jesinsky, Aaron Higgins – InternsDr. Tim Menzies, Ph.D. - Director

Pier Luigi Long – NASA IV&V

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