Self Doubt

Question

Suppose we have priority-based processes. Which scheduler will replace a low priority process which is presently executing when a high priority process arrives in the ready queue?

Also which scheduler is responsible for pulling out a process from CPU if it requests I/O?

Answer 1

Long term scheduler: This scheduler is responsible to move the process which are ready for processing to ready queue. It also regulates degree of multiprogramming. It is also called job scheduler.

Short term scheduler: This scheduler is responsible to move processes from ready queue to CPU and also from CPU to ready queue. It is also called CPU scheduler.

Medium term scheduler: It swaps the process from CPU to blocked state which requests for i/o. It moves the process from main memory to secondary memory so that other process which is ready to execute can be loaded to main memory. It is also called swapping scheduler.
 

Comments

 

 

Long term scheduler: This scheduler is responsible to move the process which are ready for processing to ready queue

From where? Main Memory or secondary memory?

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Since it is from Job queue to ready queue and job queue is maintained in secondary memory and ready queue in primary memory. So from secondary memory to primary memory.

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Swapping a blocked process from the SM to MM is done by Long term or medium-term scheduler?

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@tusharb medium term scheduler

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The answer is pretty simple, priority based scheduling is non-preemptive so once a job is given to CPU then it has to complete execution and newly arrived job can’t be preempted ,this problem was solved by modifying priority based scheduling but in that case new problem arises termed as Starvation.

Answer 2

When a process in the CPU asks for I/O, there is a special scheduler called the I/O Scheduler that takes care of managing the communication between the CPU and the I/O devices. The I/O Scheduler handles the I/O request and makes sure that the CPU is not left idle while waiting for the I/O operation to complete. It may decide to suspend the current process and choose another process from the ready queue to execute on the CPU, ensuring efficient utilization of system resources.