01 Process and Scheduling

Operating System

Process & [email protected]

WHAT ?

Process is a program in executionprocess execution must progress in sequential fashion

a process includes:

1. program counter

2. stack

3. data section

Process in Memory

2operating system process

Process State (important)

As a process executes, it changes state

New : The process is being created

Running : Instructions are being executed

Waiting : The process is waiting for some event to occur

Ready : The process is waiting to be assigned to a processor

Terminated : The process has finished execution

3operating system - process

Diagram of Process State


Process Control Block (PCB)

Information associated with each process

Process state

Program counter

CPU registers

CPU scheduling information

Memory-management information

Accounting information

I/O status information

Where is it ?


CPU Switch From Process to Process


Process Scheduling Queues

Job queue set of all processes in the system

Ready queue set of all processes residing in main memory, ready and waiting to execute

Device queues set of processes waiting for an I/O device

Processes migrate among the various queues


Representation of Process Scheduling


Schedulers

Long-term scheduler (or job scheduler) selects which processes should be brought into the ready queue

Short-term scheduler (or CPU scheduler) selects which process should be executed next and

allocates CPU


Addition of Medium Term Scheduling


Context Switch (important)

When CPU switches to another process, the system must save the state of the old process and load the saved

state for the new process

Context of a process represented in the PCB

Context-switch time is overhead; the system does no useful work while switching

Time dependent on hardware support


Process Creation

Parent process create children processes, which, in turn create other processes, forming a tree of

processes

Process identified and managed by a processidentifier (pid)


Process Creation (cont)

UNIX examples (UNIX ????)

fork system call creates new process

exec system call used after a fork to replace the process memory space with a new program


Process Termination

Process executes last statement and asks the OS to delete it (exit)Output data from child to parent

Process resources are deallocated by OS

Parent may terminate execution of children processes (abort)Child has exceeded allocated resources

Task assigned to child is no longer requiredparent is exiting

Some operating system do not allow child to continue if its parent terminates

All children terminated - cascading termination

operating system - process 14

Interprocess Communication

Processes may be independent or cooperating (Can affect or be affected by other processes, including

sharing data)

Why cooperating ?Information sharing , Computation speedup ,

Modularity, and Convenience

Two models of IPC :Shared memory & Message passing


IPC modelWhich one is message passing ?

Which one is Shared memory ?


SCHEDULING

Dispatcher

selects from among the processes in memory that are ready toexecute, and allocates the CPU to one of them

decide when a process :1. running to waiting state2. running to ready state3. waiting to ready state4. Terminates

Scheduling under 1 and 4 is nonpreemptive All other scheduling is preemptive

operating system CPU Scheduling 18

Scheduling Factor1. CPU utilization - keep the CPU as busy as possible

must be maximized2. Throughput - number of processes that complete their execution

per time unit must be maximized

3. Turnaround time - amount of time to execute a particular processmust be minimized

4. Waiting time - amount of time a process has been waiting in the ready queuemust be minimized

5. Response time - amount of time it takes from when a request was submitted until the first response is produced, not output (for timesharing environment)must be minimized


SCHEDULING METHOD

FIRST COME FIRST SERVE (FCFS / FIFO)

SORTHEST JOB FIRST (SJF)

PRIORITY BASED

ROUND ROBIN


References

1. Abraham Silberschatz, Peter Baer Galvin, Greg Gagne, Operating System Concepts With Java,

Wiley


Assignment 2

Make report about your experiment in dual boot

Experiment 1 - Windows Linux

1. Explain detail steps to install windows and then linux on the same machine/pc

2. Explain about GRUB, or LILO according to the installation

Experiment 2 Linux windows x

1. Explain detail steps to install linux and then windows on the same machine/pc

2. Is there any difference installation steps between 1st experiment and 2nd

3. How about the GRUB or LILO, is it all right ? or anything is missing ? Explain how toovercome the missing thing (if there is something wrong)


SUBMISSION

Submit your report to elearning

REPORT must contain :

1. Cover page : Student id, and bla bla bla

2. Explanation important step of those experiments

3. References

Format : AS2-.pdf (eg. AS2-5214100010.pdf)


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01 Process and Scheduling