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Questions tagged [process-scheduling]

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

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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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27 views

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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Job shop scheduling variant with non-sequential process plans

As the title says, I am looking for a variant of the job shop scheduling problem which allows for non-sequential process plans. For example, I might have a job whose task-order constraints look like ...
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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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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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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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Two Process Solution for Critical Section Problem- Algorithm 1

I have started learning Critical Section Problem and its various solutions. To explain my question, let me first give a brief background of it. The general structure for a two Process Solution for ...
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200 views

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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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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1answer
123 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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70 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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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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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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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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Notion of CPU burst in Time Sharing Operating Systems

As far as I understand OS calculates the CPU burst of a process based on its historical values and then may use algorithms like SJF etc for scheduling. But what if the OS is time sharing, where the "...
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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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Worst turn around time

This is a question I found in a previous year's exam: Can RR ever be the worst possible CPU scheduling algorithm in terms of turn around time? If so, under what circumstances? I don't quite ...
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Scheduling in multi core processor

I have an exercise. Let's say we have a system with two computing cores A and B. There are four processes P1(10,A), P2(5,A), P3(13,A), P4(2,B). The number is the next extinction in CPU and the letter ...
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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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374 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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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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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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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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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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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
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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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108 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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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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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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1answer
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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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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 ...
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why p1 misses it first deadline? Rate monotonic scheduling

I understand that rate monotonic scheduling assigns a priority to a process based on the periodicity of the tasks it generates and the process with the shortest inter-task period has the highest ...
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How does CFS prevent a long sleeping task from occupying the CPU?

The Completely Fair Scheduler executes the task that has so far received the least share of CPU time and is thus the most 'disadvantaged'. So if a task sleeps for a really long time, say 3hrs, how ...
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Does a context switch happen when a process has terminated?

I know this might sound like a newbie question but let's say we have a priority based scheduling algorithm (non-preemptive) where all processes arrive at time 0 and based on priority the order is P1, ...
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Round Robin Scheduling

I understand that a big advantage of round robin scheduling over non-preemptive schedulers is that it dramatically improves average response times. By limiting each task to a certain amount of time, ...
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Understanding google's user level threads in kernel threads

I came across Paul Turner work on increasing efficiency of M:N threading model. I am not able to grasp the concept at slide 18 of LPC-User-Threading It says : for two threads ...
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Scheduling identical jobs with Cmax/Ci

I have $x$ uniform machines that are identical, except that each runs at a different speed; machine $j$ runs at speed $s_j$. I have $n$ identical jobs. Each machine can handle one job at a time. ...
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How to schedule n jobs that come at different times on 1 machine (each taking a different time to complete the task)?

Let's say I have to do n jobs, and each job can be done at or after a time T(i) (1<=i<=n). And we have 1 machine and the machine takes a time M to do any job whatsoever. The machine once started ...
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Round Robin Scheduling: No process in Ready Queue

First post here, glad I found this exchange. I am in my Operating Systems course at university learning process scheduling. In my homework assignment we have to fill out a simulated scheduling chart ...
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Paging: Does the page table of a process also gets swapped out when the process gets swapped out from main memory?

Does a process's page table too gets swapped out to secondary storage from main memory when the process gets swapped out to secondary storage from main memory? And gets swapped back in when the ...
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1answer
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Is there a generic word for “thread or process”?

I'm writing about a problem that could be caused by race conditions between multiple threads, or OS-level processes on the same machine or different machines, or VM-level processes like the Erlang VM ...
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Number Partitioning targeting a Ratio of subset sums?

I have a problem, which appears to be similar to number partitioning: a set of numbers partitioned (two-way), such that the sum of the numbers in each subset are as close as possible to a targeted ...
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Characterize an OS as multiprogrammed OS

Which of the following features will characterize an OS as multiprogrammed OS? More than one program may be loaded into main memory at the same time. If a program waits for certain event another ...
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Does a time quantum affect priority non preemptive scheduling?

I am given a list of processes with their arrival time, CPU, time and Priority. The time quantum is given as 2 seconds. A lower priority number translates to a higher priority. (process #, arrival ...