Misconceptions About Realtime Computing : A Serious Problem for Nextgeneration Systems

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Misconceptions About Real-time Computing A
Serious Problem for Next-generation Systems
J. A. Stankovic, Misconceptions about Real-Time
Computing A Serious Problem for Next Generation
Systems, IEEE Computer, 21(10), pp. 10-19,
October 1988.
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There is no science in RT system design

• Most good science grew out of attempts to solve
  practical problems
• Real-time system engineers need help
• The first flight of a space shuttle was delayed
  due to a subtle timing bug due to a transient
  overload during system initialization
• A scientific framework to prevent such a bug to
  be included is needed
• Real-time scheduling, resource management, RT
  programming language,

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Advances in supercomputer hardware will cover RT
requirements

• One can exploit parallel processors to improve
  throughput
• It does not mean timing constraints can be met
  automatically
• Unless HW is designed to perfectly match the
  application, the processors and their
  communication subsystems may not be able to
  handle all of the task load and time-critical
  traffic
• Real-time task and communication scheduling can
  get harder as more hardware is used

4

• Demand for computational power often exceeds
  supply
• Intelligent management of finite resources is
  required

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RT Computing Fast Computing

• RT computing
• The objective of fast computing is to minimize
  the average response time
• The objective of real-time computing is to meet
  the individual timing requirement of each task
• Meet individual task deadlines
• Fast computing cannot necessarily provide
  predictability
• Fastest hardware software used in the space
  shuttle failed to support the timing requirements
• Testing is not the answer

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• Fast is relative
• Worst case, not average case, response time
  matters
• Not speed but predictability is the goal
• Functional and timing behaviors should be as
  deterministic as necessary to satisfy system
  specification
• Guarantee the delay is shorter than the upper
  bound
• Predictability is not only hardware or
  algorithmic issue
• The delay statement in Ada only specifies the
  minimum delay before the next task is scheduled
• Many things, including scheduling theory,
  software design, formal methods, RTOS, can change
  things

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RT Programming Assembly Coding, Priority
Interrupt Programming, Device Driver Writing

• Hand-coding may have more bugs, especially large
  RT program
• Objective in RT research
• Automate
• Customized resource scheduler from
  timing-constraint spec.

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RT System Research Performance Engineering
Common misconceptions(5)

• To investigate effective resource allocation
  strategies to satisfy timing-behavior requirement
  (Perf. Engineering)
• Specification verification of timing behavior
• Programming language semantics
• Theoretical problems

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Main Research Issues

• Specification and verification
• Modeling and verification of systems that are
  subject to timing constraints
• RT scheduling theory
• Meet the specified timing requirements
• Support the utilization bound to meet all
  deadlines
• Meet as many deadlines as possible, if it is
  impossible to meet all deadlines

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Main Research Issues

• RTOS
• Guarantee RT constraint
• Support FT and distribution
• Scheduling time-constrained resource allocation
• RT programming language and design methodology
• High level abstraction to deal with complex
  real-time systems
• Management of time
• Schedulability check
• Reusable RT software module

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Main Research Issues

• (Distributed) RTDB
• Concurrency in transaction processing
• RT scheduling algorithm
• Fault tolerance
• Formal specification of the timing constraints
• Error handling
• RT system architecture
• Interconnection topology (process, I/O)
• Fast, reliable, and time-constrained
  communication
• Cost-effective and integrated fashion
• WCET analysis

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Main Research Issues

• RT communication
• End-to-end deadlines
• Packet scheduling
• Dynamic routing
• Network buffer management
• Wireless Sensor Networks
• Newly emerging area
• Small, inexpensive, wireless sensors for RT
  sensing control