processscheduler-150319224416-conversion-gate01.pdf
- 2. CONTENT…
- 4. PROCEES SCHEDULER A series of action or steps taken in order to achieve a particular end. A program that arranges computer’s operation into an appropriate sequence. A machine that organizes or maintain schedulers. A process is a program during execution
- 5. PROCESS SCHEDULER INTRODUCTION: Multiprogramming is to have some process running at all times, to Maximum CPU Utilization. To meet these objectives, the Process Scheduler selects available process for a program execution of the CPU. For a single-processor system, there will never be more than one running process, if there are more processes, the rest will have to wait until the CPU is free and can be Rescheduled. A process migrates among the various scheduling queues throughout its lifetime. The operating system must select, for scheduling purpose, processes from these queues in some fashion. The selection process is carried out by the appropriate Scheduler. Often, in Batch System, more processes are submitted than can be executed immediately. These processes are spooled to a mass-storage device(Disk), where they are kept for later execution. The Long-term scheduler, or Job scheduler, selects processes from this pool and loads them into memory for execution. Whenever the CPU becomes IDLE the operating system must select one of the processes in the Ready Queue to be executed. The Short-term scheduler, or CPU scheduler, selects from among the processes that are ready to execute and allocates the CPU to one of them.
- 7. start Terminated Diagram of process state Start to Ready= Long Term Scheduler Ready to Running= Mid Term Scheduler Running to Waiting or waiting to ready= Short Term Scheduler
- 9. TYPES OF PROCESS SCHEDULERS…… S.NO TYPES 1 Process Scheduler/CPU Scheduler 1.) Preemptive 2.) Non-Preemptive 2 Long- Term Scheduler 3 Medium- Term Scheduler 4 Short-Term Scheduler 5 Dispatcher
- 10. Process Scheduler /CPU Scheduler Process scheduler is a part of the operating system that decides which process runs at a certain point in time. When CPU becomes idle the OS must select one of the processes in Ready Queue to be executed CPU Scheduler selects a process from the processes in memory that are ready to execute (from Ready queue),allocates the CPU to one of them CPU scheduling decisions may take place when a process: Switches from running to waiting state Terminates Switches from running to ready state. (e.g. when time slice of a process expires or an interrupt occurs) Switches from waiting to ready state. (e.g. on completion of I/O) On arrival of a new process The OS code that implements the CPU scheduling algorithm is known as CPU scheduler
- 11. In Pre-emptive scheduling the currently running process may be interrupted and moved to the ready state by OS (forcefully) In Non-preemptive Scheduling, the running process can only lose the processor voluntarily by terminating or by requesting an I/O. OR, Once CPU given to a process it cannot be preempted until the process completes its CPU burst Pre-emptive scheduling & Non-preemptive scheduling
- 12. Long Term Scheduler Determines which programs are admitted to the system for processing Controls the degree of multiprogramming More processes, smaller percentage of time each process is executed
- 13. Medium Term Scheduler Part of the swapping function Based on the need to manage the degree of multiprogramming
- 14. Short Term Scheduling Known as the dispatcher Executes most frequently Invoked when an event occurs Clock interrupts I/O interrupts Operating system calls
- 15. Scheduling Criteria Maximum Utilization of CPU Waiting time should be minimum Turn around time should be minimum Response time should be minimum Arrival time should be minimum Note:- Total time taken by the process is called Turn around time.