Questions about how operating systems decide which process to execute at which time.

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Is bounded waiting ensured in given version of Dekker's solution for critical section problem?

William Stallings discuss various step by step process in developing Dekker's algorithm in his Operating Systems book. In process, he reaches to following version of algorithm (which is incomplete as ...
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1answer
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Peterson's vs. Bakery Algorithm

From my CS course, the Peterson's Algorithm and the Bakery Algorithm both are solutions which satisfy the 3 requirements of any solution to the critical section problem. a) What are their adv/disadv ...
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1answer
35 views

How does the OS Scheduler give/take control of HW?

Imagine a uniprocessor system with a simple operating system with non-threaded processes and basic virtual memory (paging, no segmentation, no replacement to disk, etc). Now assume a simple ...
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confusion between process's weight and load balance in CFS

Oki So Im trying to get into the bottom of kernel cfs and the load balancer. each process Virutal Run Time equals to : (Wo/Wp)*PR where Wo equals to weight of nice value zero. Wp equals process ...
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1answer
28 views

Two threads are waiting on a mutex. Which one is unblocked?

Suppose there are three threads A, B, C and thread A has acquired a mutex lock and it is processing. If threads B and C try to acquire the same mutex, they will be blocked according to the mutex lock ...
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4answers
58 views

Operating System - CPU scheduling Decisions

I understand that CPU scheduling takes place on 4 circumstances listed below: When the process changes state from Running to Ready Changes state from Running to Waiting Changes state from Waiting to ...
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1answer
52 views

example for weakly fair v.s. strongly fair scheduling in concurrency

I am having difficult time understanding the difference between weakly fair and strongly fair schedulers. Can someone provide an example and explain how they are different? for reference, here are ...
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1answer
105 views

How and which component of an Operating System is responsible for the transition of a process from the blocked state to the ready queue?

A process in an Operating System is considered to occupy several states and a process transitions between these states. A scheduler is responsible for assigning CPU time to a process. However, a ...
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1answer
44 views

Which process comes first?

Let's say we have 3 processes: Process 1 service time 6 arrival time 0 Process 2 service time 2 arrival time 1 Process 3 service time 5 arrival time 3 We know that: after 1 time, process 2 will ...
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1answer
113 views

Can you explain this exercise solution to me? [closed]

A process running on CTSS (Compatible Time Sharing System) needs 30 quanta to complete. How many times must it be swapped in, including the very first time (before it has run at all)? • Answer : The ...
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1answer
486 views

Highest Response Ratio Next (Scheduling Algorithm)

In CPU scheduling HRRN(Highest Response Ratio Next) algorithm chooses the next process to be scheduled using the formula (W+S)/S where W-> waiting time & S->Service Time. Can someone share their ...
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Problems of cyclic executive approach for scheduling of real time systems

I have a doubt on the cyclic executive approach for scheduling on real time systems. From Alan Burns's book Real-time Systems and Programming Languages. This final property represents one of the ...
2
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1answer
437 views

Operating system processes

I'm a bit confused about this question: "Multiple jobs can run in parallel and finish faster than if they had run sequentially. Suppose that two jobs, each needing 10 minutes of CPU time, start ...
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1answer
118 views

User level threads are transparent to the kernel?

Find whether given statement True or False? Explain. User level threads are transparent to the kernel? My attempt : False. Since, user level threads are managed by a user level library ...
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1answer
281 views

How does the OS determine the CPU burst time of a process?

This question is related to OS. After having solved many problems in CPU scheduling I was wondering how does the CPU know the burst time of all the processes in the main memory before executing them? ...
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2answers
35 views

Is the program in secondary memory can be a process?

Let us consider the following scenario, The cpu started executing a program, which is in secondary memory with n lines of code, so, it brings m ( < n ) lines of code in to main memory and started ...
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0answers
61 views

Processes running in Distributed Systems (Advanced Operating System)

I had a test today, there was a question that was a bit confusing. Anyway I am asking the question, from memory, and explaining what I answered. It would be great if someone could explain if I did ...
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2answers
210 views

Difficulty understanding pre-emptive vs non-preemptive CPU scheduling

I'm having difficulty understanding what my book is trying to say in regards to preemptive and non-preemptive CPU scheduling. It says the following: CPU Scheduling decisions may take place under ...
2
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1answer
347 views

Starvation Condition in CPU/Process Scheduling?

Let's say OS is using preemptive CPU scheduling. A process P1 gets a chance to run for some time and then next higher priority process comes and preempts P1. After that higher priority processes are ...
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1answer
76 views

Can the processor just turn off the interrupt request line?

I was doing some of the interrupts question online and found this Multiple choice question How can the processor ignore other interrupts when it is servicing one a) By turning off the interrupt ...
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0answers
50 views

Optimality of EDF

For Earliest Deadline First, I have read that if utilization is less or equal to 1, the task set is schedulable under EDF. But does this criteria expresses the optimality for EDF? If not, how can we ...
3
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1answer
89 views

Time quantum assignment to processes

In a book I am reading it is stated that an input/output intensive process should receive a higher time quantum whereas a computing intensive process on the other hand should receive a lower one. Here ...
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0answers
53 views

Processes concurrency

I am getting ready for my end of year exams and I got stuck on this question. Consider the following 3-process concurrent program which uses semaphores S1, ...
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58 views

Efficiency of incorporating enhancement

I've been having problems finding the efficiency of an enhanced processor, here is the question: Suppose that we want to enhance the processor used for Web serving. The new processor is 10 ...
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1answer
218 views

What is a student process?

According to Galvin and Silberschatz, 5 queues are maintained in multilevel queue scheduling, each for: System Process Interactive Process Interactive Editing Process Batch process Student ...
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1answer
576 views

Can Shortest Job First Scheduling be subject to convoy effect?

Look at the below table for example : Look at the Non-Preemptive SJF table Suppose if the burst time of process $P_1$ was a very large number compared to $7$, the processes $P_3,P_2$ and $P_4$ have ...
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2answers
225 views

Switching between user-level and kernel-level threads

After reading difference between user-level threads and kernel-level threads ,now I am in doubt of context switching.Context switching is managed by OS when switching between processes/threads but ...
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1answer
118 views

Round-Robin Scheduler - What exactly is the quantum time used for?

Suppose you have three stages for a job: Creation stage = the job gets created Executing stage = the job is executed/served Finishing stage = the job is "marked" as finished. Now, say the quantum ...
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1answer
352 views

How are system calls handled in a virtual machine?

Quoting wikipedia, a system call is: In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services (e.g. ...
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2answers
505 views

What guarantees do “soft” real-time operating systems actually provide

I think I know what a "hard" real-time operating system is. It is an operating system with a scheduler that provides a contract with the application programmer. An application provides a deadline ...
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1answer
54 views

Which process states exist a multi-processor machine?

In a single-processor architecture, A process might be New, Ready, Running, Blocked and Terminated. Are there any additional states in a multi-processor architecture?
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112 views

Does a multi cpu system not improve the first come first serve (fcfs) cpu scheduling algorithm?

I created a program that simulates the fcfs scheduling algorithm. First I implemented it for a single core, then modified it for four homogenoues cpus. I compared the results with several datasets, ...
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1answer
759 views

How does the OS know the physical address of a process' first memory page?

If I have a program, its instructions are stored on the hard drive. When I double-click the executable the pages of memory for this process must get loaded in to RAM. However, for the pages to get ...
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0answers
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How can I talk about priority inversion if it's impossible to specify priority?

In the paper: Leslie Lamport: What It Means for a Concurrent Program to Satisfy a Specification: Why No One Has Specified Priority; ACM Symp Principles of Programming Languages, (POPL-12):78-83, ...
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1answer
197 views

How to build/recognise a deadlock-free order of resources

I have been faced with a problem where three concurrent processes X, Y ,Z execute three different code segments that access and update certain shared variables. Before entering the respective code ...
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1answer
2k views

Exponential averaging for SJF CPU scheduling

Calculate the exponential averaging with $T_1 = 10$, $\alpha=0.5$ and the algorithm is SJF with previous runs as $8,7,4,16$. 9 8 7.5 None I am getting 4. None as the answer. ...
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1answer
911 views

What happens when time slices are too short or too long?

What bad things can occur when the lengths of the time slices in a multitasking system are too small? What can happen when they are too big? How should the length of the time slice be chosen?
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1answer
148 views

processes response time confusion

An OS contains 10 identical processes that were initiated at the same time.Each process contains 15 identical requests. Each request consume 20 msec of CPU time.A request is followed by an I/O ...
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1answer
417 views

A variant of job assignment (scheduling) problem with variable time span

The problem is a scheduling problem with n jobs and k machines. Each job i can be started at any time, but its duration is not exactly known except a time span interval. For example, a job may take ...
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2k views

Disk scheduling and process scheduling

Whats the diffrence between Disk scheduling and process scheduling? I mean i know the roles of disks and processes, but it seems to me they both have the same aim. to reduce monopolies, they even both ...
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2answers
15k views

The convoy effect in process scheduling

As I understand the convoy effect, in the context of vehicular traffic in a road system. A slow moving group of vehicles passes through the system, slowing traffic even in areas which were not ...
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3answers
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What is the difference between Multiprogramming and Multitasking

I am finding it difficult to clearly differentiate between Multiprogramming and Multitasking. My primary source has been Wikipedia, but the WP article seems to be a little at odds with some less ...
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299 views

What mechanisms prevent a process from taking over the processor forever?

Suppose a process keeps running code (e.g. an infinite loop). How can other programs take over? What prevents the process from remaining active forever?
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1answer
131 views

Process state in multi threaded process

What would be the process state in a multi threaded process, in which threads are in different states (running, waiting, blocked etc)
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1answer
901 views

Scheduling algorithms and quantum time

I would like to know what impacts does a scheduling algorithm say Round Robin of FIFO have on a Operating system. I understand the a scheduling algorithm has the processes run in burst then switch ...
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1answer
996 views

How are threads implemented in different OSs?

I was reading Linux Kernel Development by Robert Love, where I came across this Linux takes an interesting approach to thread support: It does not differentiate between threads and normal ...
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4answers
8k views

What is meant by interrupts in the context of operating systems?

I've decided to read Operating Systems Concepts by Silberschatz, Galvin Gagne (8th edition) over the summer. I've gotten to a topic that's confusing me - interrupts and their role as it relates to ...
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4answers
32k views

What is the average turnaround time?

For the following jobs: The average wait time would be using a FCFS algorithm: (6-6)+(7-2)+(11-5)+(17-5)+(14-1) -> 0+5+6+10+13 -> 34/5 = 7 (6.8) What would the average turnaround time be?
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1answer
5k views

Which queue does the long-term scheduler maintain?

There are different queues of processes (in an operating system): Job Queue: Each new process goes into the job queue. Processes in the job queue reside on mass storage and await the allocation of ...
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692 views

Round-robin scheduling: allow listing a process multiple times?

In a round-robin scheduler, adding a process multiple times to the process list is a cheap way to give it higher priority. I wonder how practical an approach this might be. What benefit does it have ...