Job scheduling algorithms: Which is best for your workflow?
Job scheduling algorithms are critical to optimizing the execution of tasks on a CPU in computer science. These algorithms determine the order in which jobs are executed to improve efficiency, reduce waiting times and enhance overall system performance by optimizing resource allocation. But even more important than the algorithms you choose for your workflow are the tools you equip yourself with to enable success.
What are the 4 major job scheduling algorithms?
The four major job scheduling algorithms are first-come first-served (FCFS), shortest job first (SJF), round-robin scheduling (RR) and priority scheduling. Each algorithm has its own characteristics and is suitable for specific scenarios.
First-come first-served (FCFS) is a job scheduling algorithm that executes jobs based on their arrival time to the system. This algorithm is an example of non-preemptive scheduling, and implementation is based on first in first out (FIFO). FCFS is popular because of its simplicity, but it has downsides like longer average waiting times for short jobs, which can cause the convoy effect — a phenomenon where shorter jobs are delayed due to a long-running process occupying the CPU..
Shortest job first (SJF) prioritizes jobs that can be processed in the shortest amount of time, making it one of the most efficient algorithms for reducing average waiting time and turnaround time. However, SJF can lead to starvation if shorter jobs continuously enter the system, delaying longer jobs indefinitely. A preemptive version of SJF, called shortest remaining time first (SRTF) can interrupt the current running process if a new job with a shorter burst time arrives in the ready queue.
In round-robin (RR) scheduling, each job has a defined time slice, and the sequence of jobs cycles through in a time-sharing manner. The round-robin scheduling algorithm ensures no job monopolized the CPU, but frequent synchronization and context-switching for preemption can lower CPU efficiency for a large number of processes.
The priority scheduling algorithm is non-preemptive priority-based, labeling jobs as high-priority processes, lower-priority processes or highest-priority processes. Jobs are then executed in a priority queue. If jobs have the same priority, they’re executed in a FIFO queue. Priority scheduling works well for batch systems.
First-come first-served vs. the shortest job first algorithm
When comparing the most widely-used two job scheduling algorithms: FCFS and SJF, there are a number of elements to consider, including CPU utilization, average waiting time and job throughput.
FCFS and SJF are both non-preemptive algorithms, but they differ in prioritizing job execution. FCFS schedules new jobs by arrival time, while SJF prioritizes jobs with the shortest execution time.
FCFS advantages:
- Simplicity in implementation
- Fair execution based on arrival time
Limitations of the FCFS scheduling algorithm present in longer average waiting times and poor turnaround time. If a long job arrives first in a ready state, all subsequent jobs have to wait for its completion. This can cause significant turnaround times for jobs that otherwise could have been executed quickly in the shortest remaining time.
SJF advantages:
- Reduced average waiting times
- Efficient handling of short jobs, leading to better CPU utilization
A limitation associated with SJF is the possibility of starvation. If shorter jobs are continuously entering the system, longer jobs may end up sitting there until it’s too late. Optimal performance of the SJF algorithm is dependent on accurate job duration estimation, which isn’t always available or requires internal resources to obtain. This can strain the computer science team if they have to spend time creating data structures for the algorithm to run properly.
The best job scheduling algorithms for each operating system
Deciding which job scheduling algorithm to use depends on a variety of factors, including job requirements, programming language like JavaScript or HTML, system architecture, development resources and more. Some algorithms work better with certain technologies and operating systems.
Best job scheduling algorithm for Mac operating system
One of the commonly employed scheduling algorithms on Mac operating systems is the multilevel feedback queue (MLFQ) algorithm. Multilevel queue scheduling is often used to optimize the execution time of tasks on the CPU. The MLFQ algorithm is a dynamic priority scheduling algorithm that categorizes jobs into multiple priority queues. It allows for jobs to move between queues based on runtime, processing time and priority.
In a Mac operating system, the MLFQ algorithm can handle a mix of interactive tasks, background tasks and real-time tasks effectively by assigning appropriate priorities. This algorithm ensures that interactive tasks, which require fast response times, are given higher priority, while background tasks and less time-sensitive jobs are assigned lower priorities. This approach helps maintain system responsiveness, prompt completion time for tasks and fast response time for new jobs.
Best job scheduling algorithm for Windows operating system
In the Windows operating system, the default job scheduling algorithm used is the MLFQ algorithm. Windows also supports a subset of scheduling algorithms through its Windows Scheduler API, including FCFS, SJF, RR and priority scheduling.
The Windows Scheduler API allows developers and system administrators to customize job scheduling algorithms based on specific job requirements.
Best job scheduling algorithm for Linux operating system
Choosing the best job scheduling algorithm for Linux depends on the specific Linux distribution, kernel version and requirements of the system. A widely-used and highly regarded scheduling algorithm for Linux is the Completely Fair Scheduler (CFS).
The Completely Fair Scheduler is a process scheduler that fairly distributes CPU time among active processes. It utilizes a red-black tree data structure to maintain a queue of runnable processes, allowing for programmatic scheduling decisions. The CFS algorithm considers factors like process priority, virtual runtime and load balancing to ensure fair distribution and optimal resource utilization.
There are other job and process scheduling algorithms and options compatible with Linux. These include the Real-Time Scheduler (SCHED_FIFO), which prioritizes real-time tasks, and the Deadline Scheduler (SCHED_DEADLINE), which guarantees timely execution for tasks with strict deadlines.
Managing job scheduling algorithms with RunMyJobs by Redwood
RunMyJobs is a powerful tool for managing job scheduling algorithms, providing developers the flexibility to customize and optimize their workflows. It’s possible to easily implement various scheduling algorithms based on specific requirements.
One of the advantages of RunMyJobs is support for priority scheduling. This feature is useful in real-time systems where certain jobs require immediate attention or have strict deadlines.
It also offers MLFQs, enabling the execution of jobs in multiple priority levels. Teams can easily move jobs between queues based on processing time, priority and runtime. This feature provides a balance between short and long jobs, preventing starvation and optimizing system performance.
