Questions tagged [process-scheduling]
Questions about how operating systems decide which process to execute at which time.
133
questions
2
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1answer
1k 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 ...
1
vote
1answer
542 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 ...
1
vote
0answers
288 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
votes
1answer
1k 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 ...
1
vote
0answers
117 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,
...
3
votes
2answers
3k 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 Process ...
2
votes
1answer
4k 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 ...
1
vote
2answers
3k 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 ...
0
votes
1answer
892 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 ...
4
votes
1answer
2k 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. ...
17
votes
3answers
2k 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 ...
3
votes
1answer
78 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?
0
votes
1answer
321 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, ...
4
votes
1answer
4k 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 ...
2
votes
0answers
40 views
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 Speciļ¬cation: Why No One Has Speciļ¬ed Priority; ACM Symp Principles of Programming Languages, (POPL-12):78-83, ...
0
votes
1answer
362 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 ...
0
votes
3answers
10k 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.
But ...
0
votes
1answer
4k 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?
1
vote
1answer
404 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 ...
3
votes
1answer
602 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 ...
0
votes
2answers
5k 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 ...
6
votes
4answers
26k 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 ...
12
votes
3answers
26k views
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 ...
3
votes
2answers
4k 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?
2
votes
1answer
270 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)
3
votes
2answers
2k views
Scheduling algorithms and quantum time
I would like to know what impacts does a scheduling algorithm, let's say Round Robin or FIFO, have on an Operating System. I understand that a scheduling algorithm has the processes run in burst then ...
7
votes
1answer
2k 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 ...
9
votes
4answers
13k 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 ...
7
votes
6answers
111k 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?
6
votes
2answers
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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 ...
9
votes
2answers
1k 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 ...
asked Mar 11 '12 at 21:39
Gilles 'SO- stop being evil'
39.9k7 gold badges107 silver badges171 bronze badges
10
votes
1answer
1k views
Are two-level schedulers only useful to manage swapping?
Two-level scheduling is useful when a system is running more processes than fit in RAM: a lower-level scheduler switches between resident processes, and a higher-level scheduler swaps groups of ...
asked Mar 11 '12 at 21:24
Gilles 'SO- stop being evil'
39.9k7 gold badges107 silver badges171 bronze badges
19
votes
4answers
2k views
Does cooperative scheduling suspend processes when they perform an I/O operation?
Many operating systems references say that with cooperative (as opposed to preemptive) multitasking, a process keeps the CPU until it explicitly voluntarily suspends itself. If a running process ...
