Questions tagged [process-scheduling]

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

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Finding the timestamps of processes implementing Lamport's clocks

I have been asked this question, but don't know how to go about answering it. Three process, which are implementing Lamport's clocks, are running and a lot of events are taking, place including some ...
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110 views

Scheduling of process manufacturing with setup times

Overview The process manufacturing is (in contrast to discrete manufacturing) focused on the production of continuous goods such as oil. The planning is typically solvable by means of Linear ...
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27 views

How to compute this CPU scheduling exercise?

How can I compute this type of problem? My doubts are one the number of jobs, I have tried drawing a Gantt chart, but it becomes huge and unmanageable. How am I supposed to represent the results? ...
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42 views

Questions regarding CPU scheduling algorithms ( Round Robin and Priority scheduling )

Consider the following processes : 1) My First Question is if we need to schedule them using preemptive priority scheduling with Round-Robin for equal processes priorities with a quantum of 3. Here ...
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Preemptive priority scheduling problem with same priority

So if T1(priority 3, arrived first) was preempted it is put back to the runqueue. If there is already T4(priority 3, arrived fourth) inside the runqueue, which one of these two will be handled first?! ...
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In completely fair scheduler in Linux, how to calculate the initial virtual run time of a process

I am trying to implement a completely fair scheduler. I want to know how to calculate the initial value of virtual run time of a process in order to insert the process into a red black tree
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93 views

What is cold-start penalty ? What are some ways to reduce it?

when a new process is created using a fork() function, there is a cold start penalty, what is this and why does it happen?
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Round Robin time slice(quantum time)

In all books about this topic, I read that there is a rule of thumb is that 80% of the process execution time is lower than time slice. But how do I calculate this value? I looked at every article ...
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107 views

Advantages of Preemptive Scheduling

I'm currently studying for an exam which includes operating systems. I'm solving the exams from previous years and I'm stuck on a particular question: "One of the advantages of preemptive scheduling ...
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Does pre-emption of a process occur when that process is busy waiting?

I was reading about Peterson's Solution for Synchronisation. Let's assume the two shared variables to be int bool flag[2] and ...
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33 views

How does a dual core microprocessors run so many programs?

I have a laptop with Intel dual core and it runs, the OS windows, and many application from Opera, age of empires, word, excel etc open at once just fine. If it only has 2 cores, how can so many ...
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36 views

When does a semaphore issue a wait and when does it issue a signal?

In my textbook, Operating Systems: Internals and Design Principles (9th Edition) by William Stallings in chapter 5, it explains how semaphores work: The fundamental principle is this: Two or more ...
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Process scheduling accounting for multiple factors

I'm attempting to solve a problem that consists of scheduling two types (A and B) of processes to run. The system must be non-preemptive (once a process starts executing it must finish before another ...
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Expected value of next CPU burst using exponential averaging

The burst time is needed for Shortest Job First (SJF) and Shortest Run Time First (SRTF) scheduling. To get the approximate burst time, we use the equation $$\tau_{n + 1} = t_n + (1 - \alpha)\tau_n$$ ...
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What is Round Robin's behavior when a process comes at the same time that the old process is swapped out?

Let's say there are two processes: p1 and p2, their arrival time and service time are 0,2 and 3,1 respectively. The time quantum is 2s. After excuting for two seconds, will the processor excute p2 ...
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How to do Distributed Job Scheduling after the Leader was elected and slaves are known - (bully)

I'm building a system that processes key,value pairs on a continuous basis in a loop, until terminated. How do I schedule tasks on the leader and make slaves execute them? This is a realm of ...
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42 views

Calculation of speed up of a program executed in multi-threaded system

Speed up of execution of a program is to be calculated within a multi-threading rather than a single thread system. The program's 30% instruction can be executed serially & rest can be executed ...
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Segmentation with paging

Question: A virtual memory system uses both paging and segmentation. Process virtual addresses consist of a total of 32 bits. The page size is 1024 (210) bytes. A page table may occupy at most one ...
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261 views

How exactly does a CPU do process scheduling?

I know in theory how various scheduling algorithms work, such as round robin, where each process is given small time slices to run a few instructions, before the operating system passes execution onto ...
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Calculating minimum processing time for many recipes and tools

I originally asked this question on StackOverflow but a comment was made to the effect that my problem pertains to Job Shop Scheduling and that it was more of a comp sci problem than a programming ...
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28 views

What approach to solve an open shop problem with following constraints

Say we have an open shop scheduling problem with following constraints : No wait-time between operations of a job Multiple job types (meaning each job type has different set of operations eventhough ...
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1answer
140 views

Can a schedule be conflict serializable but not serializable?

A schedule is called conflict serializable if it can be transformed into a serial schedule by swapping non-conflicting operations. Then, My question is: Can a schedule be conflict serializable but ...
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760 views

Appreciation of the 5 state process model

I'm starting out in an Operating Systems module. I have a few understanding questions to think about, which will not be gone through in class. A process state model is an abstraction (or model) which ...
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Difference between Response time, Execution time, and CPU time

I studied Computer Architecture from David A. Patterson and have came across the idea of Response time. Response time also called Execution time. The total time required for the computer to ...
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multithreading - duration of jobs

" How long will it take for 2 jobs to complete if they're running in parallel, knowing that both have a total of 20 minutes of CPU usage time and 50% IO" I calculated the CPU usage: ...
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200 views

Round-Robin fashion exercise

In my Operating Systems class I have an exercise to sketch out how a round-robin algorithm would apply to a specific scenario, which is the following: Now the correction that I was provided with by ...
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181 views

Proccess scheduling arrival time

If I have a set of processes, let's say 9 and I know the burst time and the waiting time for SJF algorithm and also know that processes arrive in groups of 3 processes at M1 moment, M2 moment, M3 ...
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144 views

Why are threads called the unit of dispatch?

Threads called the "unit of dispatch" but what does that mean? I was looking over the web and two operating systems books but I can't find the answer. It seems that processes are defined by two ...
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74 views

Rate Monotonic maximum execution time

There are several periodic tasks (Period, Execution time), e.g.: A = (20, 9) B = (12, 4) C = (4, X) What methods/tests can be used for finding the maximum execution time X for which the task ...
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63 views

Why does the operating system switch an active process to different cores?

When running a single-threaded application that is 'always busy', on a multi-core computer, modern operating systems will typically switch the process from one core to another from time to time. Even ...
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1answer
50 views

Can a process run if there's not enough space for minimum pages?

I'm studying OS and I came up with this scenario where the OS works with a paging scheme and virtual memory, and a process wants to start running, but in memory, there's not enough space to allocate ...
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OS process management

Assume a process execution interrupted at the middle and CPU started executing a different process.How does the OS handle this situation?
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1k views

What is the relation between Time Sharing operating systems and Round Robin CPU scheduler?

So i have asked this before, but i still didn't get my answer so I'll try to make my question more clear this time : Based on my O.S book, Time sharing operating systems switch between processes ...
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2k views

Arrival Time vs Burst Time vs Priority Time? If Priority Time is the same, which process dispatch first?

The question is based on if we have the same Priority value when we are given: Arrival Time = AT, Priority and Burst Time=BT. 1.Say if we a table with AT, Priority and BT. To dispatch a process it is ...
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693 views

Difference between Time-sharing computers and computers which use Round Robin scheduling algorithm?

So maybe I'm confused in these concepts but i thought that time sharing computer is a computer which the processor switches between different processes quickly to achieve a good response time but ...
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Appropriate algorithm or heuristic for task scheduling

I'm sure this problem has been addressed before, but I'm unable to find an exact description of it. I have $m$ machines, and $n$ tasks that need processing. Each task takes a variable amount of ...
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87 views

What is the difference between a page and thread?

"Each process that is executed is divided into blocks of same size, called pages." "Thread is a part of process being executed." Are pages and threads both part(s) of process? Whats the difference ...
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long-lived scheduling using max-flow & push/relabel

I'm writing a scheduler of long-lived Processors which execute long-lived Tasks. Processors and Tasks may each come and go over time, at any time (when a Processor departs, its assigned Tasks now ...
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692 views

Questions about Amdahl's law?

Doing exam papers now and I came across two questions which I cannot get my head around sadly. Both are regarding Amdahl's law and Parallel Computing but they seem rather simple and frustratingly ...
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3k views

Operating Systems - SJN/Round Robin - turn around time + waiting time

2.(10 pts) a) You are given 4 processes in a batch system that all arrive at time 0 with the following CPU burst times: P1 : 35, P2: 25, P3: 13, P4: 22. Assuming there is no context switch ...
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73 views

Existence of Real-Time Multiprocessor Schedule

Does an algorithm exist to check for the existence of a Real-Time Multiprocessor Schedule for aperiodic hard tasks(all of which have the same Release time)? Assumptions: The processors are Uniform ...
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675 views

How can a spinlock progress when it's busy-waiting?

I read that in spinlock, process keeps on waiting for the lock continuously in a loop until it receives signal(lock) or ...
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1answer
603 views

Troubles understanding this Interval Scheduling question

Can someone explain how to prove what this question is asking? I'm terrible at proofs and the fact that I don't even understand the hint is very troubling. This is a homework question. Consider the ...
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149 views

Why TurnAround Time is considered as Performance Metric for Scheduling Algorithms?

I know what is turn around time but i am confused why wating time is not considred as Performance Metric for Scheduling Algorithms Since it gives the time for which a Process will wait till it gets ...
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51 views

Should we assume both processes are getting same CPU clock while we solve SYNCHRONIZATION problems in uniprocessor system?

In synchronization, when one process is in a critical section & another is busy waiting, both are using CPU. But in a uni processor system, in the same clock both cant get the CPU. So there must ...
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2k views

Process Synchronization: Dekker's algorithm

This Screenshot is taken from William Stalling's Operating Systems book. My doubt is that Bounded wait is not satisfied by this solution. For example: P0 and P1 both want to enter critical section ...
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543 views

Convoy effect in priority scheduling and SJF (Non preemptive)

In books, I have read that FCFS suffers from convoy effect. I think that even SJF and priority(both preemptive and non preemptive) can suffer from convoy effect. In SJF, if a process with large burst ...
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158 views

Numerator of HRRN scheduling formula

In the HRRN scheduling, priority formula is P = (W+E)/E , where W: waiting time and E: estimated run time. CPU finds the job that has highest priority value and does that job. However, the formula ...
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What is the best Approximation algorithm to schedule a task graph?

If I have a task graph T and want a schedule to optimize the make-span, what is currently the best approximation algorithm for this problem? Are there any constant approximation algorithms?
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Where to start on SJF Cpu schedualing homework problem?

So the question is; For the following three jobs: P1: 10 (3,2,5); P2: 4 (2,2); P3: 16 (2,3,5,6) Execute the three jobs using Exp Ave Alpha =0.6, default=2 I know the formula to get the exponential ...