GATE CSE 2001 | Question: 2.20

Question

Which of the following does not interrupt a running process?

• A. A device
• B. Timer
• C. Scheduler process
• D. Power failure

Comments

It is not easy but tagged easy :p

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Interrupt is generated when any IO device or any process wants to communicate to CPU or any other process to inform something, while preemption is the mechanism where OS can forcefully take out any running process from running state and send it to ready state.The criteria for Preemption varies based on type of scheduling algorithm we use.

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@SammanV in interrupt  task is temporarily switched, while in preempt  control of a task is given  to another task to allow run.

Answer 1

Answer is (C).

Timer and disk both makes interrupt and power failure will also interrupt the system. Only a scheduler process will not interrupt the running process as scheduler process gets called only when no other process is running (preemption if any would have happened before scheduler starts execution).

Quote from Wikipedia

In the Linux kernel, the scheduler is called after each timer interrupt (that is, quite a few times per second). It determines what process to run next based on a variety of factors, including priority, time already run, etc. The implementation of preemption in other kernels is likely to be similar.

https://www.quora.com/How-does-the-timer-interrupt-invoke-the-process-scheduler

Comments

@Saideepak Bejawada

The timer interrupt will invoke the scheduler and the scheduler will check if any higher priority process is there in the ready queue. That process will be selected for the CPU and the dispatcher will do the context switching and all that stuffs.

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In the above question...How a device can interrupt  a running process?

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The CPU cannot execute all of these processes simultaneously, so the operating system has to choose a particular process on the basis of the scheduling algorithm used. So, this procedure of selecting a process among various processes is done by the scheduler. Once the scheduler has selected a process from the queue, the dispatcher comes into the picture, and it is the dispatcher who takes that process from the ready queue and moves it into the running state. Therefore, the scheduler gives the dispatcher an ordered list of processes which the dispatcher moves to the CPU over time.

Answer 2

Ans : None

A device can generate an Interrupt

Timer generates interrupt when time quantum is over in case of RR

Power failure will generate an interrupt

A scheduled process can also generate an interrupt in case of priority scheduling , when priority of scheduled process is more than Currently Running process

Comments

yes, agreed .

All can cause an interrupt.

A, B, D  -> Hardware interrupt.

C -> software interrupt.

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@vijaycs option (C) is scheduler process (scheduler) not scheduled process in ACE past year booklet.

Please correct the question. Read this

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according to this option D but i think all interrupt

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so how to deal with this kind of thing ??

Answer 3

A. Device will not interrupt a running process. When a device requests service, DMA will take over, so no interruption to the running process.
B. Timer obviously interrupts a running process.
C. Scheduler Process interrupts a running process and schedules some other process.
D. Power Failure definitely generates interrupt.

Answer 4

according to me option D is correct because power failure means shut down system ..so its not interrupt generated

Comments

interrupt a running process means any kind of interruption...and during power failure whole sysytem fails..all the process inside it also fails....like if u were playing a game during power failure that will also stop..means a process interrupted...none of the option matches here

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i think all interrupt generated so none of these