Question

Give an example of a scheduling discipline that is not work conserving.

Short answer

A non-work conserving discipline schedules tasks at fixed intervals regardless of queue status, like 'Time slicing with a fixed delay.'

Step-by-step solution

Understanding Work Conserving

A work-conserving scheduling discipline ensures that as long as there are tasks ready to be processed, the processor (or service system) is always busy. There is no idle time if there are pending tasks.

Identifying Non-Work Conserving Disciplines

Non-work conserving scheduling allows for the processor to be idle, even if there are tasks waiting to be completed. This can happen due to various reasons such as waiting for specific criteria to be met before execution.

Exploring the Time Slicing Technique

Time slicing techniques like 'Time slicing with a fixed delay' are examples of non-work conserving disciplines. In this method, tasks are processed at specific intervals, and the processor may remain idle between intervals regardless of task availability.

Example of Non-Work Conserving Schedule

Consider a scheduling method where tasks are only processed every 10 minutes, regardless of whether tasks are waiting. If a task finishes at 2 minutes past the interval, the processor will remain idle for 8 minutes even with available tasks.

Key concepts

Work-Conserving Scheduling

A work-conserving scheduling discipline is an efficient way to manage tasks. It ensures the processor keeps busy as long as there are tasks to handle, essentially maximizing the use of available resources. In simpler terms, if there are pending jobs lined up, a work-conserving scheduler ensures the processor doesn't sit idle.
This approach is often used in real-time systems where it's crucial to utilize resources continuously to maintain performance. The primary benefit of work-conserving scheduling is that it minimizes response time as the processor never waits idly if work needs to be done.

• This type of scheduling is optimal for systems requiring high throughput.
• It helps in reducing waiting time for tasks.
• Common scheduling algorithms like Round-Robin and Shortest Job Next can employ this discipline.

By ensuring the processor is always working if there's work to do, work-conserving scheduling aligns well with efficiency goals in computing.

Non-Work Conserving Scheduling

Non-work conserving scheduling introduces intentional idle times despite having tasks waiting to be processed. This type of scheduling is less about efficiency and more about meeting certain criteria or conditions before executing tasks. For instance, the processor might need to wait for resources, synchronization, or specific time intervals.
In the case of non-work conserving schedules, the system might hold tasks back until certain conditions are satisfied, potentially increasing response times. However, it's beneficial in contexts where tasks' executions need coordination or resource sharing.

• It mirrors scenarios where systems manage energy consumption by staying idle when high consumption isn't necessary.
• This method is also used when uniformity or predictability of task processing is prioritized over speed.
• It can be seen in fixed interval timed scheduling, where tasks. are executed at predetermined times.

While not ideal for immediate task handling, non-work conserving regimes offer controlled processing benefits in specific settings.

Time Slicing Technique

Time slicing is a scheduling strategy that divides the processor's time among various tasks in fixed durations, known as time slices. Generally, in a time slicing technique, each task is allocated a fair share of time on the processor in a cyclical manner.
In some formats, time slicing might integrate a fixed delay between slices, thus becoming non-work conserving. During these delay periods, the processor may remain idle regardless of the availability of pending tasks.
This structure is especially useful when fairness in task execution is as critical as efficiency, preventing any single task from monopolizing the system. However, it can also lead to idle periods, if the scheduling includes these intentional pause intervals.

• Time slicing is pivotal in systems where equal attention to every task is necessary.
• Even with pending jobs, a fixed delay time slicing might introduce processor idle phases.
• Round-Robin scheduling is a prime example, ensuring balanced task processing through time slices.

This method harmonizes control and fairness but may sacrifice constant activity, making it a form of non-work conserving scheduling when delays are introduced.