COTS Challenges for Embedded Systems

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Configurable Scheduling and Dispatching with the
Kokyu Framework
Chris Gill and Venkita Subramonian Department of
Computer Science Washington University, St.
Louis, MO cdgill ,venkita_at_cs.wustl.edu
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Kokyu Release Plan

• Current Status
• Data Structures, Scheduling Service in ACETAO
• Precompiler-directed configuration in TAO (old)
  RTEC
• Initial nORB dispatcher implementation
• Tight coupling between current implementations
  and interfaces
• Need greater flexibility to be really useful
• September Check-in, October Release
• Refactored versions of task, queuing data
  structures
• Extend ACE task and queue implementations,
  decouple QoS descriptors
• Factory for configuration of dispatchers
• Use configuration descriptors to compose custom
  dispatching lanes
• Parameterized with details of task and queuing
  primitives
• Decoupled scheduling service implementation
• Retain compatibility with TAO RTEC
• Retain current capabilities
• Decouple from specific IDL and RT_Info
  dependences

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Next Steps Decoupling Data Structures

• Extending ACE_Task
• Decouple priority field
• Allow alternate QoS descriptors
• Allow alternate data structures
• Parameterized Task Template
• Data structure for messages
• QoS Descriptor
• Allows Greater Flexibility
• FIFO, static prio
• EDF, MLF
• Hash, queue, heap
• Reduces Clutter
• E.g., RT_Info
• E.g., ACE_Dynamic_Message_Queue
• Allows Optimization
• Algorithmic complexity vs. availability and
  nature of information

QoS descriptor
Dispatcher
functor/data
pair
data structure
dispatch thread
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Next Steps Factory-Driven Re-Configuration

• Scheduler specifies generic configuration
  information
• (OS/global) priority of each lane
• queue discipline for each lane
• timer intervals for each lane
• (new) data structure type
• Factory uses the specification
• configures each lane
• sets thread priorities
• sets reactor timer intervals
• Implicit projection
• of scheduling requirements into generic
  dispatching substrate
• dispatcher composed at run-time from ACE
  primitives
• Extends Kokyu implementation
• for (re)configuration at run-time
• previously at (pre) compile time
• Configuration Decision Functions

Dispatcher
FIFO
FIFO
FIFO
Laxity
RMSMLF
MUF
Dispatcher
Laxity
Laxity
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Next Steps Decoupling Scheduling Service

• Separate Scheduler Implementation and Interface
• Allow use in non-TAO and even non-CORBA settings
• Above ACE but below TAO
• But, must still implement RtecScheduler
• Decouple Input/Output/Config Descriptors
• From each other
• From interfaces, scheduling models
• Goal is composability

Scheduler
tuple visitor
operation visitors