PROCESS MANAGEMENT

PROCESS MANAGEMENT Tuğba AĞCAOĞLU & Ahmet GÖKNAR

OUTLINE • What is the Process Management? What is it covers? • process state • process table, • process scheduling

Process State • Process Table(process control block) • process state • memory state • resource state • Process Scheduling

What is Multiprogramming Process • Conclusion ; Process Management

What is Process Management? • Ever action run inside a process. • In computer science, a process is an application in execution.

What is Process Management? • Operating system's way of dealing with running multiple processes. • Computing anddistributing "timeshares".

Process State • When a process is using the CPU, it is actually running and doing some work . • If a process does I/O ,the device is not ready or just slow

The process states and transitions are;

Process table • The suspended process to be restarted at a later time as if it had never been stopped • The O/S maintains information about each process in a process table

Process table • Process control blocksmust contain information about • process state • memory state • resource state

Process State • The process state must contain all the information • the value of each register • the program counter • the stack pointer

The process is in runnning, runnable, blocked

Memory state • Details of the memory allocation such as pointers to the various memory areas used by the program

Resource state • Information regarding the status of files being used by the process such as user ID

MULTI-PROGRAMMING

Process Scheduling • Processes are put into a job queue • They are kept in a list called ready queue • The ready queue is generally stored as a link list • Process waiting for a particular device are placed in a I/O queue

Process Queues cpu ready queue i/o I/O queue I/O request time slice expires child executes join fork a child wait queue resource queue resource request

Multiprogramming Process SCHEDULERS: Two types of scheduler: • Long-term schedulers (Job scheduler) • Short-term scheduler (CPU scheduler)

Multiprogramming Process • The short-term scheduler: • selects from among the processes that are ready to execute and allocates the CPU to one of them • must select a new process for the CPU frequently • must be very fast.

Multiprogramming Process The long-term scheduler : • selects processes from a batch system and loads them into memory for execution • executes less frequently

Newly arriving jobs Ready Queue Blocked Running Long-term Scheduler Short-term Scheduler SCHEDULERS

Partially-executed swapped-out processes Ready Queue CPU I/O waiting queues I/O Medium-term Scheduling end

The CPU Scheduler CPU scheduling decisions take place when a process: (i) switches from running to waiting state (ii) switches from running to ready state (iii) switches from waiting to ready (iv) terminates.

Scheduling Criteria • CPU utilization • Throughput • Turnaround time • Waiting time • Response time • Fairness

Scheduling Policies Preemptive Scheduling: • A process switched back and forth between running and ready state • More efficient , better capabilities • More complex and needs hardware support

Scheduling Policies Non-Preemptive Scheduling: • Once a process begins execution, it occupies CPU until it finishes or it blocks • Simplicity • Creates problems

SCHEDULING ALGORITHMS • First-Come-First-Served or FIFO Scheduling • Shortest-Job-first Scheduling • Priority Scheduling • Round-Robin Scheduling

FCFS Scheduling • First process will be served by CPU • Non-preemptive • Waiting time is quite long • Example

FCFS Scheduling Process CPU Burst Time (ms) P1 24 P2 3 P3 3 P1 P2 P3 0 24 27 30 Waiting time for P1 = 0; P2 = 24; P3 = 27 Ave. waiting time: (0 + 24 + 27) /3 = 17 ms.

P2 P1 P3 0 3 6 30 FCFS Scheduling Waiting time for P1 = 6; P2 = 0; P3 = 3 Ave. waiting time : (6 + 0 + 3)/3 = 3 Much better than the previous case, where we had a Convoy Effect:short process behind long process. Results in lower CPU utilization

Shortest-Job-First Scheduling • Selects the shortest job first • Enqueue jobs in order of estimated completion time • It is non-preemptive

Priority Scheduling • Assign a priority to each job and schedule jobs in order of priority • Typically low priority values = “High Priority” • Increasing priority means decrease its priority value • It can be both preemptive or non-preemptive • Equal priority processes are scheduled in FCFS order

Round-Robin Scheduling • Designed for time-sharing systems • Preemptive • Each process gets a small unit of CPU time usually 10-100 milliseconds • After that time the process preempted and added to the end of the ready queue

RESOURCES • http://computing-dictionary.thefreedictionary.com/process+table • http://en.wikipedia.org/wiki/Process_management • http://jan.netcomp.monash.edu.au/OS/l8_2.html • http://www.cs.jhu.edu/~yairamir/cs418/os2/sld007.htm • http://www.bilgiyonetimi.org/cm/pages/mkl_gos.php?nt=131 • http://gaia.ecs.csus.edu/~zhangd/oscal/pscheduling.html

PROCESS MANAGEMENT