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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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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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52 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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38 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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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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112 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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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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36 views

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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471 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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59 views

How to approach solving this variation of the Job Scheduling Problem?

Question: Given N processes with Arrival times and Processing times, calculate and print minimum number of CPUs required if maximum allowed Turnaround time for each process is 10 units. Turnaround ...
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24 views

What type of process schedulers are typically used in EKG machines?

I'm researching real-time schedulers for class, and I was trying to think of interesting examples of machines that use real-time schedulers. I thought EKGs would be a good example, so I've been trying ...
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182 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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58 views

Basics of virtual runtime - CFS Algorithm

It's known that virtual runtime is updated based on nice values of different processes and the rbtree stores different nodes based on the value of virtual runtime. If a process is doing IO, it's taken ...
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2answers
44 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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1answer
291 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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833 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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1answer
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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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3answers
254 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
326 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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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
356 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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86 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 ...
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203 views

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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1answer
157 views

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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1answer
743 views

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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671 views

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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175 views

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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1answer
182 views

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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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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1answer
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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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134 views

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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380 views

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 ...
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Does Deadlock imply Starvation

If there is a deadlock between the processes does that mean that there is starvation also? My Thinking: deadlock is no process using that resources , but starvation is like not giving chance to only ...
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I/O bound processes over CPU bound processes [closed]

will an OS which favors I/O bound processes over CPU-Bound processes, experience less average waiting time? If yes, why?
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Identify common mathematical problem behind my task in scheduling area

Having single operator, which could do work and it's time of availability - for example from 8 am till 9 pm. And operator have limited resource - let's call it ...
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Processor Scheduling (SJF / FCFS)

So I know that scheduling has been covered in other articles, but because my provided values are different and decimals are used, I am having difficulty wrapping my head around it. I have reviewed all ...
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223 views

Does throughput includes CPU idle time also?

I have 3 processes P1,P2,P3 having gantt chart as follows => Now, CPU remains idle in 0 - 2 sec and 44 - 47 seconds as I/O is taking place. Does, this affect throughput as 3 processes can be ...
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289 views

A Dead-lock in an Operating System is

A Dead-lock in an Operating System is Desirable process Undesirable process Definite waiting process All of the above My attempt: As "If a process is unable to change its state indefinitely because ...
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How to partition a digraph for later parallel computation? [duplicate]

I have a directed graph where all the nodes represent some task that needs to be computed. I need to compute the order of these tasks and also detect any cycles. Running Tarjan's algorithm on the ...
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685 views

Question on Virtual memory and Physical memory

This is the question where I'm stuck: With a 32-bit virtual address, 4 KB pages(12 offset bits), and 4 bytes per page table entry, we can compute the total page table size: Number of page table ...
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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 ...