This document discusses real-time scheduling and algorithms. It defines real-time systems as systems where correctness depends on both functional and temporal aspects. Key aspects of real-time scheduling include determinism, responsiveness, reliability and meeting deadlines. Common real-time scheduling algorithms discussed include rate monotonic scheduling, earliest deadline first, and dynamic scheduling approaches. The document also covers priority inversion which can occur when higher priority tasks must wait for lower priority tasks in preemptive multitasking systems.
This document discusses various CPU scheduling algorithms such as FCFS, SJF, priority scheduling, and round robin. It covers the basic concepts of scheduling, criteria for evaluating algorithms, examples of single processor and multiprocessor scheduling, and examples of scheduling in operating systems like Windows and Mac OS. The goal of scheduling is to allocate CPU time effectively among competing processes or threads.
Operating Systems Process Scheduling Algorithmssathish sak
The document discusses various CPU scheduling algorithms used in operating systems including first-come, first-served (FCFS), round robin (RR), shortest job first (SJF), and shortest remaining time first (SRTF). It explains the assumptions, goals, and tradeoffs of each algorithm such as minimizing response time, maximizing throughput, and ensuring fairness. Examples are provided to illustrate how each algorithm works and its performance compared to others under different conditions involving job lengths. Predicting future job lengths is also discussed as it can impact the performance of algorithms like SRTF.
Process scheduling involves assigning system resources like CPU time to processes. There are three levels of scheduling - long, medium, and short term. The goals of scheduling are to minimize turnaround time, waiting time, and response time for users while maximizing throughput, CPU utilization, and fairness for the system. Common scheduling algorithms include first come first served, priority scheduling, shortest job first, round robin, and multilevel queue scheduling. Newer algorithms like fair share scheduling and lottery scheduling aim to prevent starvation.
The document discusses several key process scheduling policies and algorithms:
1. Maximum throughput, minimize response time, and other policies aim to optimize different performance metrics like job completion time.
2. Common scheduling algorithms include first come first served (FCFS), shortest job next (SJN), priority scheduling, round robin, and multilevel queues. Each has advantages for different workload types.
3. The document also covers process synchronization challenges like deadlock and livelock that can occur when processes contend for shared resources in certain ordering. Methods to avoid or recover from such issues are important for system design.
This presentation talks about Real Time Operating Systems (RTOS). Starting with fundamental concepts of OS, this presentation deep dives into Embedded, Real Time and related aspects of an OS. Appropriate examples are referred with Linux as a case-study. Ideal for a beginner to build understanding about RTOS.
This document summarizes key concepts from Chapter 5 of the textbook "Operating System Concepts - 8th Edition" regarding CPU scheduling. It introduces CPU scheduling as the basis for multiprogrammed operating systems. Various scheduling algorithms are described such as first-come first-served, shortest job first, priority scheduling, and round robin. Criteria for evaluating scheduling algorithms include CPU utilization, throughput, turnaround time, waiting time, and response time. Ready queues can be partitioned into multiple levels with different scheduling policies to implement multilevel queue and feedback queue scheduling.
CPU scheduling allows processes to share the CPU by pausing execution of some processes to allow others to run. The scheduler selects which process in memory runs on the CPU. There are four types of scheduling decisions: when a process pauses for I/O, switches from running to ready, finishes I/O, or terminates. Scheduling can be preemptive, where a higher priority process interrupts a running one, or non-preemptive. Common algorithms are first come first serve, shortest job first, priority, and round robin. Real-time scheduling aims to process data without delays and ensures the highest priority tasks run first.
This document discusses various CPU scheduling algorithms such as FCFS, SJF, priority scheduling, and round robin. It covers the basic concepts of scheduling, criteria for evaluating algorithms, examples of single processor and multiprocessor scheduling, and examples of scheduling in operating systems like Windows and Mac OS. The goal of scheduling is to allocate CPU time effectively among competing processes or threads.
Operating Systems Process Scheduling Algorithmssathish sak
The document discusses various CPU scheduling algorithms used in operating systems including first-come, first-served (FCFS), round robin (RR), shortest job first (SJF), and shortest remaining time first (SRTF). It explains the assumptions, goals, and tradeoffs of each algorithm such as minimizing response time, maximizing throughput, and ensuring fairness. Examples are provided to illustrate how each algorithm works and its performance compared to others under different conditions involving job lengths. Predicting future job lengths is also discussed as it can impact the performance of algorithms like SRTF.
Process scheduling involves assigning system resources like CPU time to processes. There are three levels of scheduling - long, medium, and short term. The goals of scheduling are to minimize turnaround time, waiting time, and response time for users while maximizing throughput, CPU utilization, and fairness for the system. Common scheduling algorithms include first come first served, priority scheduling, shortest job first, round robin, and multilevel queue scheduling. Newer algorithms like fair share scheduling and lottery scheduling aim to prevent starvation.
The document discusses several key process scheduling policies and algorithms:
1. Maximum throughput, minimize response time, and other policies aim to optimize different performance metrics like job completion time.
2. Common scheduling algorithms include first come first served (FCFS), shortest job next (SJN), priority scheduling, round robin, and multilevel queues. Each has advantages for different workload types.
3. The document also covers process synchronization challenges like deadlock and livelock that can occur when processes contend for shared resources in certain ordering. Methods to avoid or recover from such issues are important for system design.
This presentation talks about Real Time Operating Systems (RTOS). Starting with fundamental concepts of OS, this presentation deep dives into Embedded, Real Time and related aspects of an OS. Appropriate examples are referred with Linux as a case-study. Ideal for a beginner to build understanding about RTOS.
This document summarizes key concepts from Chapter 5 of the textbook "Operating System Concepts - 8th Edition" regarding CPU scheduling. It introduces CPU scheduling as the basis for multiprogrammed operating systems. Various scheduling algorithms are described such as first-come first-served, shortest job first, priority scheduling, and round robin. Criteria for evaluating scheduling algorithms include CPU utilization, throughput, turnaround time, waiting time, and response time. Ready queues can be partitioned into multiple levels with different scheduling policies to implement multilevel queue and feedback queue scheduling.
CPU scheduling allows processes to share the CPU by pausing execution of some processes to allow others to run. The scheduler selects which process in memory runs on the CPU. There are four types of scheduling decisions: when a process pauses for I/O, switches from running to ready, finishes I/O, or terminates. Scheduling can be preemptive, where a higher priority process interrupts a running one, or non-preemptive. Common algorithms are first come first serve, shortest job first, priority, and round robin. Real-time scheduling aims to process data without delays and ensures the highest priority tasks run first.
The document discusses various concepts related to process management in operating systems including process scheduling, CPU scheduling, and process synchronization. It defines a process as a program in execution and describes the different states a process can be in during its lifecycle. It also discusses process control blocks which maintain information about each process, and various scheduling algorithms like first come first serve, shortest job first, priority and round robin scheduling.
The document discusses different CPU scheduling algorithms used in operating systems. It describes first-come, first-served (FCFS) scheduling, which schedules processes in the order they arrive. Shortest job first (SJF) scheduling prioritizes the shortest jobs. Round-robin (RR) scheduling allocates each process a time slice or quantum to use the CPU before switching to another process. The document also covers shortest remaining time next, preemptive priority scheduling, and some of the criteria used to evaluate scheduling algorithms like CPU utilization, throughput, waiting time and response time.
It consists of CPU scheduling algorithms, examples, scheduling problems, realtime scheduling algorithms and issues. Multiprocessing and multicore scheduling.
Hello....
Dear views
Scheduling is most important Role in OS..... in this ppt i described very Creatively about Process Scheduling...... I hope you like it..... and easily understand it...... :-) :-)
Embedded System,
Real Time Operating System Concept
Architecture of kernel
Task
Task States
Task scheduler
ISR
Semaphores
Mailbox
Message queues
Pipes
Events
Timers
Memory management
Introduction to Ucos II RTOS
Study of kernel structure of Ucos II
Synchronization in Ucos II
Inter-task communication in Ucos II
Memory management in Ucos II
Porting of RTOS.
This document discusses different types of scheduling algorithms used by operating systems to determine which process or processes will run on the CPU. It describes preemptive and non-preemptive scheduling, and provides examples of common scheduling algorithms like first-come, first-served (FCFS), shortest job first (SJF), round robin, and priority-based scheduling. Formulas for calculating turnaround time and waiting time are also presented.
The document discusses CPU scheduling in operating systems. It describes how the CPU scheduler selects processes that are ready to execute and allocates the CPU to one of them. The goals of CPU scheduling are to maximize CPU utilization, minimize waiting times and turnaround times. Common CPU scheduling algorithms discussed are first come first serve (FCFS), shortest job first (SJF), priority scheduling, and round robin scheduling. Multilevel queue scheduling is also mentioned. Examples are provided to illustrate how each algorithm works.
The document discusses various scheduling algorithms used in operating systems including:
- First Come First Serve (FCFS) scheduling which services processes in the order of arrival but can lead to long waiting times.
- Shortest Job First (SJF) scheduling which prioritizes the shortest processes first to minimize waiting times. It can be preemptive or non-preemptive.
- Priority scheduling assigns priorities to processes and services the highest priority process first, which can potentially cause starvation of low priority processes.
- Round Robin scheduling allows equal CPU access to all processes by allowing each a small time quantum or slice before preempting to the next process.
Scheduling is a method used to allocate computing resources like processor time, bandwidth, and memory to processes, threads, and applications. It aims to balance system load, ensure equal distribution of resources, and prioritize processes according to set rules. There are different types of scheduling including long-term, medium-term, and short-term scheduling. Scheduling algorithms decide which process from the ready queue is allocated the CPU based on whether the policy is preemptive or non-preemptive. Common algorithms include first-come first-served, shortest job first, priority scheduling, and round-robin scheduling.
Round Robin is a preemptive scheduling algorithm where each process is allocated an equal time slot or time quantum to execute before being preempted. It is designed for time-sharing to ensure all processes are given a fair share of CPU time without starvation. The process is added to the back of the ready queue when its time slice expires. It provides low response time on average but increased context switching overhead compared to non-preemptive algorithms. The time quantum value impacts both processor utilization and response time.
This document discusses real-time scheduling algorithms. It begins by defining real-time systems and their key properties of timeliness and predictability. It then discusses two common real-time scheduling algorithms: fixed-priority Rate Monotonic scheduling and dynamic-priority Earliest Deadline First scheduling. It covers how each algorithm prioritizes and orders tasks, and analyzes their schedulability and utilization bounds. It concludes by comparing the two approaches.
Sara Afshar: Scheduling and Resource Sharing in Multiprocessor Real-Time Systemsknowdiff
PhD Candidate,
Department of Computer science
Mälardalen University
Time: Tuesday, Dec. 30, 2014, 11:30 a.m.
Location: Computer Engineering Department, Urmia University
Abstract:
The processor is the brain of a computer system. Usually, one or more programs run on a processor where each program is typically responsible for performing a particular task or function of the system. The performance of all the tasks together results in the system functionality. In many computer systems, it is not only enough that all tasks deliver correct output, but it is also crucial that these activities are delivered in a proper time. This type of systems that have timing requirements are known as real-time systems. A scheduler is responsible for scheduling all tasks on the processor, i.e., it dictates which task to run and when to run to ensure that all tasks are carried out on time. Typically, such tasks/programs need to use the computer system’s hardware and software resources to perform their calculation. Examples of such type of resources that are shared among programs are I/O devices, buffers and memories. Technology that is used for the management of shared resources is known as resource sharing synchronization protocol.
In recent years, a shift from single-processor platforms to multiprocessor platforms has become inevitable due to availability of processor chips and requirements on increased performance. Scheduling and resource sharing protocols have been well studied for uniprocessor systems. However, in the context of multiprocessors, still such techniques are not fully mature. The shift towards multi-core technology has revealed the demand for real-time scheduling algorithms along with synchronization protocols to support real-time applications on multiprocessors, both with and without dependencies.
In this talk, we first have an introduction to real-time embedded systems. Next, we look at scheduling and resource sharing policies in uniprocessor platforms. Further, we discuss the extension of scheduling and resource sharing policies for multiprocessor platforms and present the recent challenges arisen in this context.
Biography:
Sara Afshar is a PhD student at Mälardalen University. She has received her B.Sc. degree in Electrical Engineering from Tabriz University, Iran in 2002. She worked at different engineering companies until 2009. In the year 2010 she started her M.Sc. in Embedded Systems at Mälardalen University. She obtained her Master degree in 2012 and at the same year she started her PhD studies in Mälardalen University. Currently she is working on the topic of resource sharing in multiprocessor systems. She is part of the Complex Real-Time Embedded Systems group at Mälardalen University.
The document discusses various CPU scheduling algorithms including first come first served, shortest job first, priority, and round robin. It describes the basic concepts of CPU scheduling and criteria for evaluating algorithms. Implementation details are provided for shortest job first, priority, and round robin scheduling in C++.
The components of an operating system all exist in order to make the different parts of a computer work together. All user software needs to go through the operating system in order to use any of the hardware, whether it be as simple as a mouse or keyboard or as complex as an Internet component.
About real time system task scheduling basic concepts.It deals with task, instance,data sharing and their types.It also covers various important terminologies regarding scheduling algorithms.
This document provides an overview of real-time operating systems (RTOS), including their key characteristics, scheduling approaches, and commercial examples. RTOS are used in applications that require tasks to complete work and deliver services on time. They use priority-based and clock-driven scheduling algorithms like rate monotonic analysis and earliest deadline first to ensure real-time constraints are met. Commercial RTOS aim to provide features like priority levels, fast task preemption, and predictable interrupt handling for real-time applications.
Multilevel queue scheduling divides processes into groups based on properties like type and resource usage. These groups are placed into multiple queues, each with a different priority level. Higher priority queues like the system process queue use scheduling algorithms like FCFS, while lower priority queues like the student process queue use priority scheduling. This approach allows different scheduling optimizations based on the process type compared to a single queue approach. A disadvantage is the potential for lower priority processes to starve if higher priority processes monopolize resources.
1) A semaphore consists of a counter, a waiting list, and wait() and signal() methods. Wait() decrements the counter and blocks if it becomes negative, while signal() increments the counter and resumes a blocked process if the counter becomes positive.
2) The dining philosophers problem is solved using semaphores to lock access to shared chopsticks, with one philosopher designated as a "weirdo" to avoid deadlock by acquiring locks in a different order.
3) The producer-consumer problem uses three semaphores - one to limit buffer size, one for empty slots, and one for locks - to coordinate producers adding to a bounded buffer
The document discusses the key components and structure of operating systems. It covers:
1) The main components of an OS include process management, memory management, I/O management, secondary storage management, file management, protection systems, accounting systems, and more.
2) Traditionally, OSes were structured as monolithic kernels containing all components, but this poses reliability and maintenance issues. Alternative structures include layering and microkernels.
3) Layering implements an OS as a set of layers, where each layer provides an abstract "machine" to the layer above. This improves modularity but can hurt performance.
4) Microkernels minimize kernel code and implement OS services as user-level processes for
This document discusses scheduling in real-time operating systems (RTOS). It explains that RTOS tasks must be performed immediately to control or react to events. There are hard and soft real-time tasks, where hard tasks must be performed by a specified time or cause losses, while soft tasks can miss deadlines and be rescheduled. The RTOS scheduler prioritizes reducing response times over task handling. Scheduling can be preemptive, where higher priority tasks interrupt lower ones, or non-preemptive, where tasks must wait for others to finish. A better approach uses time-based interrupts to allow preemption of the current process if a higher priority one is ready. Scheduling algorithms are classified based on
This document proposes an efficient implementation of the slot shifting algorithm that reduces computational overhead. Slot shifting is an algorithm that schedules both periodic and aperiodic tasks by allocating spare processing capacity to aperiodic tasks. The proposed approach removes the discrete time "slots" used in slot shifting and replaces it with a method using job release times and deadlines. It also provides a way to delay capacity updates to further reduce runtime complexity while preserving the slot shifting concept. Experimental results show this new approach can reduce scheduling overhead by 45-60% on average compared to the original slot shifting algorithm. It also presents a new aperiodic task admission algorithm with lower time complexity than the existing slot shifting approach.
The document discusses various concepts related to process management in operating systems including process scheduling, CPU scheduling, and process synchronization. It defines a process as a program in execution and describes the different states a process can be in during its lifecycle. It also discusses process control blocks which maintain information about each process, and various scheduling algorithms like first come first serve, shortest job first, priority and round robin scheduling.
The document discusses different CPU scheduling algorithms used in operating systems. It describes first-come, first-served (FCFS) scheduling, which schedules processes in the order they arrive. Shortest job first (SJF) scheduling prioritizes the shortest jobs. Round-robin (RR) scheduling allocates each process a time slice or quantum to use the CPU before switching to another process. The document also covers shortest remaining time next, preemptive priority scheduling, and some of the criteria used to evaluate scheduling algorithms like CPU utilization, throughput, waiting time and response time.
It consists of CPU scheduling algorithms, examples, scheduling problems, realtime scheduling algorithms and issues. Multiprocessing and multicore scheduling.
Hello....
Dear views
Scheduling is most important Role in OS..... in this ppt i described very Creatively about Process Scheduling...... I hope you like it..... and easily understand it...... :-) :-)
Embedded System,
Real Time Operating System Concept
Architecture of kernel
Task
Task States
Task scheduler
ISR
Semaphores
Mailbox
Message queues
Pipes
Events
Timers
Memory management
Introduction to Ucos II RTOS
Study of kernel structure of Ucos II
Synchronization in Ucos II
Inter-task communication in Ucos II
Memory management in Ucos II
Porting of RTOS.
This document discusses different types of scheduling algorithms used by operating systems to determine which process or processes will run on the CPU. It describes preemptive and non-preemptive scheduling, and provides examples of common scheduling algorithms like first-come, first-served (FCFS), shortest job first (SJF), round robin, and priority-based scheduling. Formulas for calculating turnaround time and waiting time are also presented.
The document discusses CPU scheduling in operating systems. It describes how the CPU scheduler selects processes that are ready to execute and allocates the CPU to one of them. The goals of CPU scheduling are to maximize CPU utilization, minimize waiting times and turnaround times. Common CPU scheduling algorithms discussed are first come first serve (FCFS), shortest job first (SJF), priority scheduling, and round robin scheduling. Multilevel queue scheduling is also mentioned. Examples are provided to illustrate how each algorithm works.
The document discusses various scheduling algorithms used in operating systems including:
- First Come First Serve (FCFS) scheduling which services processes in the order of arrival but can lead to long waiting times.
- Shortest Job First (SJF) scheduling which prioritizes the shortest processes first to minimize waiting times. It can be preemptive or non-preemptive.
- Priority scheduling assigns priorities to processes and services the highest priority process first, which can potentially cause starvation of low priority processes.
- Round Robin scheduling allows equal CPU access to all processes by allowing each a small time quantum or slice before preempting to the next process.
Scheduling is a method used to allocate computing resources like processor time, bandwidth, and memory to processes, threads, and applications. It aims to balance system load, ensure equal distribution of resources, and prioritize processes according to set rules. There are different types of scheduling including long-term, medium-term, and short-term scheduling. Scheduling algorithms decide which process from the ready queue is allocated the CPU based on whether the policy is preemptive or non-preemptive. Common algorithms include first-come first-served, shortest job first, priority scheduling, and round-robin scheduling.
Round Robin is a preemptive scheduling algorithm where each process is allocated an equal time slot or time quantum to execute before being preempted. It is designed for time-sharing to ensure all processes are given a fair share of CPU time without starvation. The process is added to the back of the ready queue when its time slice expires. It provides low response time on average but increased context switching overhead compared to non-preemptive algorithms. The time quantum value impacts both processor utilization and response time.
This document discusses real-time scheduling algorithms. It begins by defining real-time systems and their key properties of timeliness and predictability. It then discusses two common real-time scheduling algorithms: fixed-priority Rate Monotonic scheduling and dynamic-priority Earliest Deadline First scheduling. It covers how each algorithm prioritizes and orders tasks, and analyzes their schedulability and utilization bounds. It concludes by comparing the two approaches.
Sara Afshar: Scheduling and Resource Sharing in Multiprocessor Real-Time Systemsknowdiff
PhD Candidate,
Department of Computer science
Mälardalen University
Time: Tuesday, Dec. 30, 2014, 11:30 a.m.
Location: Computer Engineering Department, Urmia University
Abstract:
The processor is the brain of a computer system. Usually, one or more programs run on a processor where each program is typically responsible for performing a particular task or function of the system. The performance of all the tasks together results in the system functionality. In many computer systems, it is not only enough that all tasks deliver correct output, but it is also crucial that these activities are delivered in a proper time. This type of systems that have timing requirements are known as real-time systems. A scheduler is responsible for scheduling all tasks on the processor, i.e., it dictates which task to run and when to run to ensure that all tasks are carried out on time. Typically, such tasks/programs need to use the computer system’s hardware and software resources to perform their calculation. Examples of such type of resources that are shared among programs are I/O devices, buffers and memories. Technology that is used for the management of shared resources is known as resource sharing synchronization protocol.
In recent years, a shift from single-processor platforms to multiprocessor platforms has become inevitable due to availability of processor chips and requirements on increased performance. Scheduling and resource sharing protocols have been well studied for uniprocessor systems. However, in the context of multiprocessors, still such techniques are not fully mature. The shift towards multi-core technology has revealed the demand for real-time scheduling algorithms along with synchronization protocols to support real-time applications on multiprocessors, both with and without dependencies.
In this talk, we first have an introduction to real-time embedded systems. Next, we look at scheduling and resource sharing policies in uniprocessor platforms. Further, we discuss the extension of scheduling and resource sharing policies for multiprocessor platforms and present the recent challenges arisen in this context.
Biography:
Sara Afshar is a PhD student at Mälardalen University. She has received her B.Sc. degree in Electrical Engineering from Tabriz University, Iran in 2002. She worked at different engineering companies until 2009. In the year 2010 she started her M.Sc. in Embedded Systems at Mälardalen University. She obtained her Master degree in 2012 and at the same year she started her PhD studies in Mälardalen University. Currently she is working on the topic of resource sharing in multiprocessor systems. She is part of the Complex Real-Time Embedded Systems group at Mälardalen University.
The document discusses various CPU scheduling algorithms including first come first served, shortest job first, priority, and round robin. It describes the basic concepts of CPU scheduling and criteria for evaluating algorithms. Implementation details are provided for shortest job first, priority, and round robin scheduling in C++.
The components of an operating system all exist in order to make the different parts of a computer work together. All user software needs to go through the operating system in order to use any of the hardware, whether it be as simple as a mouse or keyboard or as complex as an Internet component.
About real time system task scheduling basic concepts.It deals with task, instance,data sharing and their types.It also covers various important terminologies regarding scheduling algorithms.
This document provides an overview of real-time operating systems (RTOS), including their key characteristics, scheduling approaches, and commercial examples. RTOS are used in applications that require tasks to complete work and deliver services on time. They use priority-based and clock-driven scheduling algorithms like rate monotonic analysis and earliest deadline first to ensure real-time constraints are met. Commercial RTOS aim to provide features like priority levels, fast task preemption, and predictable interrupt handling for real-time applications.
Multilevel queue scheduling divides processes into groups based on properties like type and resource usage. These groups are placed into multiple queues, each with a different priority level. Higher priority queues like the system process queue use scheduling algorithms like FCFS, while lower priority queues like the student process queue use priority scheduling. This approach allows different scheduling optimizations based on the process type compared to a single queue approach. A disadvantage is the potential for lower priority processes to starve if higher priority processes monopolize resources.
1) A semaphore consists of a counter, a waiting list, and wait() and signal() methods. Wait() decrements the counter and blocks if it becomes negative, while signal() increments the counter and resumes a blocked process if the counter becomes positive.
2) The dining philosophers problem is solved using semaphores to lock access to shared chopsticks, with one philosopher designated as a "weirdo" to avoid deadlock by acquiring locks in a different order.
3) The producer-consumer problem uses three semaphores - one to limit buffer size, one for empty slots, and one for locks - to coordinate producers adding to a bounded buffer
The document discusses the key components and structure of operating systems. It covers:
1) The main components of an OS include process management, memory management, I/O management, secondary storage management, file management, protection systems, accounting systems, and more.
2) Traditionally, OSes were structured as monolithic kernels containing all components, but this poses reliability and maintenance issues. Alternative structures include layering and microkernels.
3) Layering implements an OS as a set of layers, where each layer provides an abstract "machine" to the layer above. This improves modularity but can hurt performance.
4) Microkernels minimize kernel code and implement OS services as user-level processes for
This document discusses scheduling in real-time operating systems (RTOS). It explains that RTOS tasks must be performed immediately to control or react to events. There are hard and soft real-time tasks, where hard tasks must be performed by a specified time or cause losses, while soft tasks can miss deadlines and be rescheduled. The RTOS scheduler prioritizes reducing response times over task handling. Scheduling can be preemptive, where higher priority tasks interrupt lower ones, or non-preemptive, where tasks must wait for others to finish. A better approach uses time-based interrupts to allow preemption of the current process if a higher priority one is ready. Scheduling algorithms are classified based on
This document proposes an efficient implementation of the slot shifting algorithm that reduces computational overhead. Slot shifting is an algorithm that schedules both periodic and aperiodic tasks by allocating spare processing capacity to aperiodic tasks. The proposed approach removes the discrete time "slots" used in slot shifting and replaces it with a method using job release times and deadlines. It also provides a way to delay capacity updates to further reduce runtime complexity while preserving the slot shifting concept. Experimental results show this new approach can reduce scheduling overhead by 45-60% on average compared to the original slot shifting algorithm. It also presents a new aperiodic task admission algorithm with lower time complexity than the existing slot shifting approach.
Survey of Real Time Scheduling AlgorithmsIOSR Journals
This document summarizes and reviews real-time scheduling algorithms. It discusses both static and dynamic scheduling algorithms for real-time tasks on uniprocessors and multiprocessors. The document reviews algorithms such as Earliest Deadline First, Least Laxity First, and Modified Instantaneous Utilization Factor Scheduling. It concludes that Modified Instantaneous Utilization Factor Scheduling provides better results than previous algorithms in terms of context switching, response time, and CPU utilization for uniprocessor scheduling.
This document discusses real-time systems and operating systems. It defines real-time systems as those that must complete work and deliver services on time. Hard real-time systems have fatal consequences for missed deadlines, while soft real-time systems have degraded performance. Real-time operating systems use scheduling algorithms like priority scheduling to deterministically allocate CPUs and resources. They also address issues like priority inversion and interrupt handling to ensure timing constraints are always met.
Scheduling Definition, objectives and types Maitree Patel
Scheduling is the process of determining which process will use the CPU when multiple processes are ready to execute. The objectives of scheduling are to maximize CPU utilization, throughput, and fairness while minimizing response time, turnaround time, and waiting time. There are three main types of schedulers: long-term schedulers manage process admission to the system; short-term or CPU schedulers select the next process to run on the CPU; and medium-term schedulers handle process suspension during I/O waits.
This document discusses various concepts related to scheduling processes in operating systems. It covers the objectives of scheduling including maximizing CPU utilization and throughput while minimizing turnaround time and waiting time. It also discusses different types of scheduling algorithms like first-come first-served, shortest job first, priority scheduling, and round robin. For each algorithm, it provides details on how it works and its advantages and disadvantages. The document also covers different types of systems like batch, interactive, and real-time systems and the criteria used for scheduling in each.
This document contains information about real-time operating systems and scheduling algorithms. It discusses the architecture of real-time systems, including hard and soft real-time systems. It also covers common task categories and why scheduling is needed. The document then summarizes several important scheduling algorithms for real-time systems, including rate monotonic, deadline monotonic, earliest deadline first, least laxity first, and maximum urgency first. It provides examples and explanations of how each algorithm works.
The document discusses process schedulers. It defines scheduling as allowing one process to use the CPU while another process is on hold waiting for resources. The objectives of scheduling are to make the system efficient, fast, and fair. There are three types of schedulers: long term schedulers which select processes to load into memory, short term (CPU) schedulers which select the next process to run on the CPU, and medium term schedulers which swap processes in and out of memory during I/O waits. Common scheduling algorithms discussed include first come first serve, shortest job first, longest job first, round robin, and priority-based scheduling.
The document discusses processes, CPU scheduling, and process synchronization. It covers:
- Process concepts including states like running, ready, waiting, and terminated.
- CPU scheduling algorithms like first come first serve, round robin, shortest job first, and priority scheduling. Scheduling objectives are maximizing CPU utilization and minimizing wait time.
- Process synchronization is needed when multiple processes access shared resources. The critical section problem arises when processes need exclusive access to a critical section of code. Solutions ensure mutual exclusion, progress, and bounded waiting.
Scheduling involves arranging workloads and allocating resources like machinery, employees, and materials. There are two main types of scheduling: operations scheduling, which assigns jobs and employees to time periods, and flow-shop scheduling for high-volume systems, where identical products flow through standardized processes. For low-volume job shops, scheduling is more complex due to custom orders and uncertain job requirements. Key considerations for both include sequencing jobs effectively and balancing workloads across workstations.
CPU scheduling determines which process will be assigned to the CPU for execution. There are several types of scheduling algorithms:
First-come, first-served (FCFS) assigns processes in the order they arrive without preemption. Shortest-job-first (SJF) selects the process with the shortest estimated run time, but may result in starvation of longer processes. Priority scheduling assigns priorities to processes and selects the highest priority process, but low priority processes risk starvation.
LEARNING SCHEDULER PARAMETERS FOR ADAPTIVE PREEMPTIONcscpconf
An operating system scheduler is expected to not allow processor stay idle if there is any
process ready or waiting for its execution. This problem gains more importance as the numbers
of processes always outnumber the processors by large margins. It is in this regard that
schedulers are provided with the ability to preempt a running process, by following any
scheduling algorithm, and give us an illusion of simultaneous running of several processes. A
process which is allowed to utilize CPU resources for a fixed quantum of time (termed as
timeslice for preemption) and is then preempted for another waiting process. Each of these
'process preemption' leads to considerable overhead of CPU cycles which are valuable resource
for runtime execution. In this work we try to utilize the historical performances of a scheduler
and predict the nature of current running process, thereby trying to reduce the number of
preemptions. We propose a machine-learning module to predict a better performing timeslice
which is calculated based on static knowledge base and adaptive reinforcement learning based
suggestive module. Results for an "adaptive timeslice parameter" for preemption show good
saving on CPU cycles and efficient throughput time.
Learning scheduler parameters for adaptive preemptioncsandit
An operating system scheduler is expected to not al
low processor stay idle if there is any
process ready or waiting for its execution. This pr
oblem gains more importance as the numbers
of processes always outnumber the processors by lar
ge margins. It is in this regard that
schedulers are provided with the ability to preempt
a running process, by following any
scheduling algorithm, and give us an illusion of si
multaneous running of several processes. A
process which is allowed to utilize CPU resources f
or a fixed quantum of time (termed as
timeslice for preemption) and is then preempted for
another waiting process. Each of these
'process preemption' leads to considerable overhead
of CPU cycles which are valuable resource
for runtime execution. In this work we try to utili
ze the historical performances of a scheduler
and predict the nature of current running process,
thereby trying to reduce the number of
preemptions. We propose a machine-learning module t
o predict a better performing timeslice
which is calculated based on static knowledge base
and adaptive reinforcement learning based
suggestive module. Results for an "adaptive timesli
ce parameter" for preemption show good
saving on CPU cycles and efficient throughput time.
The document discusses process scheduling in operating systems. It defines process scheduling as the activity of selecting which process runs on the CPU. It describes the different queues operating systems use to manage processes, including ready, job, and device queues. It also discusses long-term, short-term, and medium-term schedulers and their roles in managing processes over different timescales. Context switching and cooperating processes are also summarized.
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The document discusses CPU scheduling in operating systems. It covers key concepts like processes alternating between CPU and I/O bursts, the role of the CPU scheduler and dispatcher in selecting the next process to run. It also describes different scheduling algorithms like FCFS, SJF, priority, and round robin scheduling and compares their advantages and disadvantages in optimizing criteria like CPU utilization, wait time, and throughput.
Real-time operating systems (RTOS) are used in embedded systems, industrial robots, and other applications that require timely and predictable responses. An RTOS guarantees tasks will complete within specified time constraints. There are two main types of RTOS designs - event-driven systems that change state in response to events, and time-sharing systems that switch tasks on a time schedule. Common RTOS scheduling algorithms include priority-based preemptive scheduling, round-robin scheduling, and fixed-priority scheduling. An RTOS must efficiently schedule tasks, provide interprocess communication, and prevent processes from accessing shared data simultaneously.
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1) Primary and secondary schedulers that prioritize threads and increase priority of non-executing threads.
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3. 3
Real-Time Systems
• Definition
– Systems whose correctness depends on their
temporal aspects as well as their functional aspects
• Performance measure
– Timeliness on timing constraints (deadlines)
– Speed/average case performance are less significant.
• Key property
– Predictability on timing constraints
4. 4
Real-Time System Example
• Digital control systems
– periodically performs the following job:
senses the system status and
actuates the system according to its current status
Control-Law
Computation
Sensor
Actuator
5.
6. What is real time computing?
Real-time computing may be defined as that type of
computing in which the correctness of the system depends
not only on the logical result of the computation but also on
the time at which the results are produced. We can define a
real-time system by defining what is meant by a real-time
process, or task.
7. A hard real-time task is one that must meet its deadline;
otherwise it will cause unacceptable damage or a fatal
error to the system.
A soft real-time task has an associated deadline that is
desirable but not mandatory; it still makes sense to
schedule and complete the task even if it has
passed its deadline.
8. Characteristics of Real-Time Operating Systems
• Determinism
• Responsiveness
• User control
• Reliability
• Fail-soft operation
9. An operating system is deterministic to the extent that it performs
operations at fixed, predetermined times or within predetermined
time intervals.
A related but distinct characteristic is responsiveness. Determinism is
con-cerned with how long an operating system delays before
acknowledging an interrupt.
Responsiveness is concerned with how long, after acknowledgment, it
takes an oper-ating system to service the interrupt. Aspects of
responsiveness include the following:
10. 1. The amount of time required to initially handle the interrupt and
begin execution of the interrupt service routine (ISR). If execution
of the ISR requires a process switch, then the delay will be longer
than if the ISR can be executed within the context of the current
process.
2. The amount of time required to perform the ISR. This generally is
dependent on the hardware platform.
3. The effect of interrupt nesting. If an ISR can be interrupted by the
arrival of another interrupt, then the service will be delayed.
11. User control is generally much broader in a real-time operating system
than in ordinary operating systems. In a typical non-real-time operating
system, the user either has no control over the scheduling function of
the operating system or can only provide broad guidance, such as
grouping users into more than one priority class.
Reliability is typically far more important for real-time systems than
non-real-time systems. A transient failure in a non-real-time system
may be solved by simply rebooting the system.
Fail-soft operation is a characteristic that refers to the ability of a
system to fail in such a way as to preserve as much capability and data
as possible.
12. To meet the foregoing requirements, real-time operating
systems typically include the following features:
• Fast process or thread switch
• Small size (with its associated minimal functionality)
• Ability to respond to external interrupts quickly
• Multitasking with interprocess communication tools such as
semaphores, signals, and events
• Use of special sequential files that can accumulate data at a fast
rate
• Preemptive scheduling based on priority
• Minimization of intervals during which interrupts are disabled
• Primitives to delay tasks for a fixed amount of time and to
pause/resume tasks
• Special alarms and timeouts
15. A real-time scheduling intended to serve real-time application
requests. It must be able to process data as it comes in, typically
without buffering delays. Processing time requirements (including
any OS delay) are measured in tenths of seconds or shorter.
Determines the order of real-time task executions
Highest priority process runs first
16.
17. Real-time scheduling is one of the most active areas of research in
computer science.
In a survey of real-time scheduling algorithms observes that the various
scheduling approaches depend on
(1) whether a system performs schedulability analysis
(2) if it does, whether it is done statically or dynamically
(3) Whether the result of the analysis itself produces a
schedule or plan according to which tasks are dispatched
at run time
18. Real time scheduling following some of the algorithms
• Static table-driven approaches: These perform a static analysis of
feasible schedules of dispatching. The result of the analysis is a schedule
that deter-mines, at run time, when a task must begin execution.
• Static priority-driven preemptive approaches: Again, a static analysis
is per-formed, but no schedule is drawn up. Rather, the analysis is used
to assign priorities to tasks, so that a traditional priority-driven
preemptive scheduler can be used.
19. • Dynamic planning-based approaches: Feasibility is determined at
run time (dynamically) rather than offline prior to the start of
execution (statically). An arriving task is accepted for execution only if
it is feasible to meet its time constraints. One of the results of the
feasibility analysis is a schedule or plan that is used to decide when to
dispatch this task.
• Dynamic best effort approaches: No feasibility analysis is
performed. The sys-tem tries to meet all deadlines and aborts any
started process whose deadline is missed
20. Static table-driven scheduling is applicable to tasks that are
periodic. Input to the analysis consists of the periodic arrival time,
execution time, periodic ending deadline, and relative priority of each
task. The scheduler attempts to develop a schedule that enables it to
meet the requirements of all periodic tasks. This is a predictable
approach but one that is inflexible, because any change to any task
requirements requires that the schedule be redone. Earliest-deadline-first
or other periodic deadline techniques are typical of this category
of scheduling algorithms.
21.
22. Static priority-driven preemptive scheduling makes use of the
priority-driven preemptive scheduling mechanism common to most
non-real-time multiprogramming systems. In a non-real-time system, a
variety of factors might be used to deter-mine priority. For example, in
a time-sharing system, the priority of a process changes depending on
whether it is processor bound or I/O bound. In a real-time system,
priority assignment is related to the time constraints associated with
each task. One ex-ample of this approach is the rate monotonic
algorithm
23.
24. dynamic planning-based scheduling-after a task arrives, but
before its execution begins, an attempt is made to create a schedule
that contains the previously scheduled tasks as well as the new
arrival. If the new arrival can be scheduled in such a way that its
deadlines are satisfied and that no currently scheduled task
misses a deadline, then the schedule is revised to accommodate the
new task
25.
26. Dynamic best effort scheduling is the approach used by many
real-time systems that are currently commercially available. When a
task arrives, the system assigns a priority based on the characteristics of
the task. Some form of deadline scheduling, such as earliest-deadline
scheduling, is typically used. Typically, the tasks are aperiodic and so no
static scheduling analysis is possible. With this type of scheduling, until
a deadline arrives or until the task completes, we do not know whether
a timing constraint will be met. This is the major disadvantage of this
form of scheduling. Its advantage is that it is easy to implement
30. Deadline scheduling is a technique that allows a user to schedule a job
by time-of-day, week, month, or year. The job's priority remains in
force, but as the deadline approaches, increases the job's priority.
Thus, deadline scheduling increases the likelihood that the job will be
scheduled for execution by the specified deadline.
As a result of deadline scheduling, a job will be reclassified when its
priority is changed.
There have been a number of proposals for more powerful and
appropriate approaches to task scheduling.
31. Real-time processes are often specified as having a start time (release
time) and a stop time (deadline). The release time is the time at which
the process must start after some event occurred that triggered the
process. For example, suppose that a collision sensor interrupt must
start airbag deployment within 20 msec. of sense time. The deadline is
the time by which the task must complete. The scheduler must allot
enough CPU time to the job so that the task can indeed complete.
There are several times of deadlines. A hard deadline is one in which
there is no value to the computation if it completes after the deadline.
32. the following information about each task might be used: :
• Ready time: Time at which task becomes ready for execution. In
the case of a repetitive or periodic task, this is actually a sequence of
times that is known in advance. In the case of an aperiodic task, this
time may be known in advance, or the operating system may only be
aware when the task is actually ready.
• Starting deadline: Time by which a task must begin.
• Completion deadline: Time by which task must be completed.
The typical real-time application will either have starting deadlines or
completion deadlines,
but not both.
33. • Processing time: Time required to execute the task to completion.
In some cases, this is supplied. In others, the operating system measures
an exponential average For still other scheduling systems.
• Resource requirements: Set of resources (other than the
processor) required by the task while it is executing.
• Priority: Measures relative importance of the task. Hard real-time
tasks may have an “absolute” priority, with the system failing if a
deadline is missed. If the system is to continue to run no matter what,
then both hard and soft real-time tasks may be assigned relative
priorities as a guide to the scheduler.
• Subtask structure: A task may be decomposed into a mandatory
subtask and an optional subtask. Only the mandatory subtask
pos1sesses a hard deadline.
34. There are several dimensions to the real-time scheduling function
when dead-lines are taken into account: which task to schedule
next, and what sort of preemption is allowed. It can be shown, for a
given preemption strategy and using either starting or completion
deadlines, that a policy of scheduling the task with the earliest
deadline minimizes the fraction of tasks that miss their deadlines
This conclusion holds both for single-processor and multi-processor
configurations.
35. As an example of scheduling periodic tasks with completion
deadlines, con-sider a system that collects and processes data from
two sensors, A and B. The dead-line for collecting data from sensor A
must be met every 20 ms, and that for B every 50 ms. It takes 10 ms,
including operating system overhead, to process each sample
of data from A and 25 mms to process each sample of data from B.
Table 10.2 summarizes the execution profile of the two tasks. Figure
10.6 compares three scheduling techniques using the execution
profile of Table 10.2. The first row of Figure 10.6 repeats the
information in Table 10.2; the remaining three rows illustrate three
scheduling techniques.
36.
37.
38. In this example, by scheduling to give priority at any preemption point
to the task with the nearest deadline, all system requirements can be
met. Because the tasks are periodic and predictable, a static table-driven
scheduling approach is used.
39. Now consider a scheme for dealing with aperiodic tasks with starting
dead-lines. The top part of Figure 10.7 shows the arrival times and
starting deadlines for an example consisting of five tasks each of which
has an execution time of 20 ms. Table 10.3 summarizes the execution
profile of the five tasks.
A straightforward scheme is to always schedule the ready task with
the earliest deadline and let that task run to completion. When this
approach is used in the example of Figure 10.7, note that although
task B requires immediate service, the service is denied. This is the risk
in dealing with aperiodic tasks, especially with starting deadlines. A
refinement of the policy will improve performance if deadlines can
be known in advance of the time that a task is ready. This policy,
referred to as earliest deadline with unforced idle times, operates as
follows: Always schedule the eligible task with the earliest deadline
and let that task run to completion.
40. task may not be ready, and this may result in the processor remaining
idle even though there are ready tasks. Note that in our example the
system refrains from scheduling task A even though that is the only
ready task. The result is that, even though the processor is not used
to maximum efficiency, all scheduling requirements are met. Finally,
for comparison, the FCFS policy is shown. In this case, tasks B and
E do not meet their deadlines.
41.
42.
43.
44. 44
RM (Rate Monotonic)
• Executes a job with the shortest period
(4,1)
(5,2)
(7,2)
Deadline Miss !
5
5
10 15
10
15
T1
T2
T3
45. 45
RM (Rate Monotonic)
• Executes a job with the shortest period
(4,1)
(5,2)
(7,2)
Deadline Miss !
5
5
10 15
10
15
T1
T2
T3
46. 46
Response Time
• Response Time (ri) [
r
i i e
• HP(Ti) : a set of higher-priority tasks than Ti
(4,1)
(5,2)
(10,2)
k
i
p
T HP T k
r e
k i
( )
5
5
10
10
T1
T2
T3
47. For RMS, the highest-priority task is the one with the shortest period,
the second highest-priority task is the one with the second shortest
period, and so on. When more than one task is available for
execution, the one with the shortest period is serviced
first. If we plot the priority of tasks as a function of their rate, the
result is a monotonically increasing function (Figure 10.8); hence the
name, rate monotonic scheduling.
48.
49.
50. One measure of the effectiveness of a periodic scheduling algorithm is
whether or not it guarantees that all hard deadlines are met. Suppose
that we have n tasks, each with a fixed period and execution time. Then
for it to be possible to meet all deadlines, the following inequality must
hold:
(10.1)
51. The sum of the processor utilizations of the individual tasks cannot
exceed a value of 1, which corresponds to total utilization of the
processor. Equation (10.1) provides a bound on the number of tasks that
a perfect scheduling algorithm can successfully schedule. For any
particular algorithm, the bound may be lower. For RMS, it can be
shown that the following inequality holds:
(10.2)
52. RM Utilization Bounds
1.1
1
0.9
0.8
0.7
0.6
0.5
1 4 16 64 256 1024 4096
The Number of Tasks
Utilization
53. Rate-monotonic assignment requires that the highest frequency
process(es) (B and C) get the highest priority and A, having the lowest
frequency of execution, gets a lower priority. If we do not follow the
rules and give A the highest priority, B the next highest, and C the
lowest, the CPU will run processes in the following order:
54. This does not give us the desired performance because, while processes
A and B get scheduled acceptably, process C is late the second time it is
scheduled and misses an entire period! Now let us reverse the priorities
as ratemonotonic assignment would dictate:
55. The scheduler can now satisfactorily meet the real-time requirements
these tasks. Rate monotonic priority assignment is guaranteed to be
optimal. If processes cannot be scheduled using rate monotonic
assignment, the processes cannot be properly scheduled with any
other static priority assignment.
56. Conclusion :
Rate Monotonic
Simpler implementation, even in systems without
explicit support for timing constraints (periods,
deadlines)
Predictability for the highest priority tasks
58. Priority inversion is a phenomenon that can occur in any
priority-based preemptive scheduling scheme but is
particularly relevant in the context of real-time scheduling.
The best-known instance of priority inversion involved the Mars
Pathfinder mission
In any priority scheduling scheme, the system should always be
executing the task with the highest priority. Priority inversion occurs
when circumstances within the system force a higher-priority task to
wait for a lower-priority task.
59. A more serious condition is referred to as an unbounded priority
inversion, in which the duration of a priority inversion depends not
only on the time required to handle a shared resource, but also on the
unpredictable actions of other unrelated tasks as well