Page 71 - DCAP608_REAL TIME SYSTEMS

Real Time Systems

Notes Questions:
1. Describe how Wawa Improves Delivery Operations with Intelligent AVL Service
does from Descartes.

2. Explain the Limited View to a Growing Network.
3. How are Improved Efficiency and reduced Costs interrelated?

Source: http://knowledge.descartes.com/resources/mobile-resource-management-performance-
management/avl—routing-scheduling-case-study-gaining-real-time-delivery-insight-with-intelligent-avl-
Wawa

6.5 Summary

 Round-robin is commonly used for scheduling time-shared applications.
 Priority-Driven Scheduling assigns priorities to jobs.
 In clock-driven scheduling, decisions on what jobs execute at what times are made at
specific time instants.

 Instants are chosen a priori before the system begins execution.
 Usually all the parameters of hard real-time jobs are fixed and known.
 The length of a round is equal to the sum of the weights of all ready jobs.
 Priority Driven Approach refers to a large class of scheduling algorithms that never leave
any resource idle intentionally.
 A resource is idle only when no job requiring the resource is ready for execution.
 Scheduling decisions are made when events such as releases and completions of jobs
occur.
 Jobs that are ready for execution are placed in a priority queue common to all processors.
 When a processor is available, the job at the head of the queue executes on the processor.
Such multiprocessor systems are referred as a dynamic system as jobs are dynamically
dispatched to processors.

 A job migrates if it starts execution on a processor, is preempted, and later resumes on a
different processor.

6.6 Keywords

Priority-driven Algorithms: This type of algorithms refers to a large class of scheduling
algorithms that never leave any resource idle intentionally. It is greedy because it tries to make
locally optimal decisions.

Round-robin Approach: It is commonly used for scheduling time-shared applications when
jobs are scheduled on a round-robin basis; every job joins a First-In-First-Out (FIFO) queue
when it becomes ready for execution.
Scheduler: It repeats a pre-computed schedule the pre-computed schedule needs to be stored
only for one major cycle.

Weighted Round-robin Algorithm: It has been used for scheduling real-time traffic in high-
speed switched networks.

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