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process and scheduling
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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
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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
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Diagram of Process State
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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 ?
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CPU Switch From Process to Process
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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
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Representation of Process Scheduling
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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
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Addition of Medium Term Scheduling
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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
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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)
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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
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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
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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
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IPC modelWhich one is message passing ?
Which one is Shared memory ?
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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
operating system CPU Scheduling 19
SCHEDULING METHOD
FIRST COME FIRST SERVE (FCFS / FIFO)
SORTHEST JOB FIRST (SJF)
PRIORITY BASED
ROUND ROBIN
operating system CPU Scheduling 20
References
1. Abraham Silberschatz, Peter Baer Galvin, Greg Gagne, Operating System Concepts With Java,
Wiley
operating system - process 21
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)
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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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